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Imaging Tutorial: Differential Diagnosis of Bright Lesions on Diffusion-weighted MR Images¹

¹ From the Departments of Radiology (T.W.S., R.R.L., M.J.O.), Neurosurgery (C.C., K.L.V.R.), and Neurology (A.M.), Academisch Ziekenhuis AZ Vrije Universiteit, Laarbeeklaan 101, 1090 Brussels, Belgium; and the Department of Radiology, Universitaire Ziekenhuizen, Leuven, Belgium (P.D.). Presented as a scientific exhibit at the 2001 RSNA scientific assembly. Received January 16, 2002, revision requested April 4, revision received and accepted August 18. Address correspondence to T.W.S. (e-mail: cradrew@az.vub.ac.be).

	Abstract

Top Abstract Basic Physics of Diffusion... Acute Infarction Venous Infarction Tumors: Glioma Tumors: Metastases Tumors: Meningioma Tumors: Lymphoma Tumors: Epidermoid Cyst Inflammation: Abscess Inflammation: Granuloma Inflammation: Encephalitis Hemorrhage Multiple Sclerosis Creutzfeld-Jakob Disease Other Bright Lesions on... References

 
High sensitivity (94%) and specificity (100%) have been reported in the diagnosis of acute cerebral infarction with diffusion-weighted magnetic resonance (MR) imaging. However, high signal intensity on diffusion-weighted MR images and low apparent diffusion coefficient values (similar to the findings in acute cerebral infarction) were reported in such diverse conditions as hemorrhage, abscess, lymphoma, and even Creutzfeldt-Jakob disease. The differential diagnosis of these conditions (eg, acute ischemic infarction and acute cerebral hemorrhage) is critical for the determination of appropriate treatment. The authors present a systematic review of bright lesions on diffusion-weighted MR images and their differential diagnosis, with emphasis on the practical and clinical approaches of differential diagnosis.

© RSNA, 2002

Index Terms: Brain, abscess, 13.256 • Brain, diseases, 13.836, 13.871 • Brain, ischemia, 13.781, 13.782 • Brain, MR, 13.12144 • Brain neoplasms, diagnosis, 13.12144 • Brain neoplasms, primary, 13.36 • Brain neoplasms, secondary, 13.38 • Encephalitis, 13.253 • Magnetic resonance (MR), diffusion study, 13.12144

	Basic Physics of Diffusion-weighted (DW) Magnetic Resonance (MR) Imaging

Top Abstract Basic Physics of Diffusion... Acute Infarction Venous Infarction Tumors: Glioma Tumors: Metastases Tumors: Meningioma Tumors: Lymphoma Tumors: Epidermoid Cyst Inflammation: Abscess Inflammation: Granuloma Inflammation: Encephalitis Hemorrhage Multiple Sclerosis Creutzfeld-Jakob Disease Other Bright Lesions on... References

 
This topic was covered in an article titled Diffusion imaging: from basic physics to practical imaging, published in RSNA EJ/RadioGraphics in 1999.

	Acute Infarction

Top Abstract Basic Physics of Diffusion... Acute Infarction Venous Infarction Tumors: Glioma Tumors: Metastases Tumors: Meningioma Tumors: Lymphoma Tumors: Epidermoid Cyst Inflammation: Abscess Inflammation: Granuloma Inflammation: Encephalitis Hemorrhage Multiple Sclerosis Creutzfeld-Jakob Disease Other Bright Lesions on... References

 
Typical Presentation on DW Images and Apparent Diffusion Coefficient (ADC) Maps
Acute ischemic lesions are characterized by high signal intensity on DW images and low ADC values. The widely accepted explanation is that the interruption of cerebral blood flow results in rapid (within minutes) breakdown of energy metabolism and ion exchange pumps. This leads to a massive shift of water from the extracellular into the intracellular compartment (cytotoxic edema) and produces a typical "bright spot" on DW MR images (1) (Figs 1, 2).

View larger version (144K): [in this window] [in a new window] [Download PPT slide]   Figure 1a.  Acute infarction within the 1st hour after stroke. (a) Fast T2-weighted spin-echo (SE) image. (b, c) DW (trace) multishot echo-planar image (b) and corresponding ADC map (c). (d, e) Perfusion-weighted multishot echo-planar imaging; (d) relative cerebral blood volume and (e) time-to-peak maps calculated from the time-intensity curve after injection of 40 mL of gadopentetate dimeglumine. (f) Time-of-flight (TOF) MR angiogram. Comments: Acute thrombosis of the right middle cerebral artery. On T2-weighted SE image, only scattered white matter hyperintensities are seen. Small occipital hyperintensity is seen on DW image, with moderate decrease in the ADC value (0.48 x 10-3 mm2/sec). There is an important perfusion deficit ("penumbra" [2]) in the middle cerebral artery territory.

View larger version (122K): [in this window] [in a new window] [Download PPT slide]   Figure 1b.  Acute infarction within the 1st hour after stroke. (a) Fast T2-weighted spin-echo (SE) image. (b, c) DW (trace) multishot echo-planar image (b) and corresponding ADC map (c). (d, e) Perfusion-weighted multishot echo-planar imaging; (d) relative cerebral blood volume and (e) time-to-peak maps calculated from the time-intensity curve after injection of 40 mL of gadopentetate dimeglumine. (f) Time-of-flight (TOF) MR angiogram. Comments: Acute thrombosis of the right middle cerebral artery. On T2-weighted SE image, only scattered white matter hyperintensities are seen. Small occipital hyperintensity is seen on DW image, with moderate decrease in the ADC value (0.48 x 10-3 mm2/sec). There is an important perfusion deficit ("penumbra" [2]) in the middle cerebral artery territory.

View larger version (124K): [in this window] [in a new window] [Download PPT slide]   Figure 1c.  Acute infarction within the 1st hour after stroke. (a) Fast T2-weighted spin-echo (SE) image. (b, c) DW (trace) multishot echo-planar image (b) and corresponding ADC map (c). (d, e) Perfusion-weighted multishot echo-planar imaging; (d) relative cerebral blood volume and (e) time-to-peak maps calculated from the time-intensity curve after injection of 40 mL of gadopentetate dimeglumine. (f) Time-of-flight (TOF) MR angiogram. Comments: Acute thrombosis of the right middle cerebral artery. On T2-weighted SE image, only scattered white matter hyperintensities are seen. Small occipital hyperintensity is seen on DW image, with moderate decrease in the ADC value (0.48 x 10-3 mm2/sec). There is an important perfusion deficit ("penumbra" [2]) in the middle cerebral artery territory.

View larger version (93K): [in this window] [in a new window] [Download PPT slide]   Figure 1d.  Acute infarction within the 1st hour after stroke. (a) Fast T2-weighted spin-echo (SE) image. (b, c) DW (trace) multishot echo-planar image (b) and corresponding ADC map (c). (d, e) Perfusion-weighted multishot echo-planar imaging; (d) relative cerebral blood volume and (e) time-to-peak maps calculated from the time-intensity curve after injection of 40 mL of gadopentetate dimeglumine. (f) Time-of-flight (TOF) MR angiogram. Comments: Acute thrombosis of the right middle cerebral artery. On T2-weighted SE image, only scattered white matter hyperintensities are seen. Small occipital hyperintensity is seen on DW image, with moderate decrease in the ADC value (0.48 x 10-3 mm2/sec). There is an important perfusion deficit ("penumbra" [2]) in the middle cerebral artery territory.

View larger version (85K): [in this window] [in a new window] [Download PPT slide]   Figure 1e.  Acute infarction within the 1st hour after stroke. (a) Fast T2-weighted spin-echo (SE) image. (b, c) DW (trace) multishot echo-planar image (b) and corresponding ADC map (c). (d, e) Perfusion-weighted multishot echo-planar imaging; (d) relative cerebral blood volume and (e) time-to-peak maps calculated from the time-intensity curve after injection of 40 mL of gadopentetate dimeglumine. (f) Time-of-flight (TOF) MR angiogram. Comments: Acute thrombosis of the right middle cerebral artery. On T2-weighted SE image, only scattered white matter hyperintensities are seen. Small occipital hyperintensity is seen on DW image, with moderate decrease in the ADC value (0.48 x 10-3 mm2/sec). There is an important perfusion deficit ("penumbra" [2]) in the middle cerebral artery territory.

View larger version (133K): [in this window] [in a new window] [Download PPT slide]   Figure 1f.  Acute infarction within the 1st hour after stroke. (a) Fast T2-weighted spin-echo (SE) image. (b, c) DW (trace) multishot echo-planar image (b) and corresponding ADC map (c). (d, e) Perfusion-weighted multishot echo-planar imaging; (d) relative cerebral blood volume and (e) time-to-peak maps calculated from the time-intensity curve after injection of 40 mL of gadopentetate dimeglumine. (f) Time-of-flight (TOF) MR angiogram. Comments: Acute thrombosis of the right middle cerebral artery. On T2-weighted SE image, only scattered white matter hyperintensities are seen. Small occipital hyperintensity is seen on DW image, with moderate decrease in the ADC value (0.48 x 10-3 mm2/sec). There is an important perfusion deficit ("penumbra" [2]) in the middle cerebral artery territory.

View larger version (147K): [in this window] [in a new window] [Download PPT slide]   Figure 2a.  Acute infarction within the first 6 hours after stroke. (a) Fast T2-weighted SE image. (b, c) DW (trace) multishot echo-planar image and corresponding ADC map. (d, e) Perfusion-weighted multishot echo-planar imaging; (d) relative cerebral blood volume and (e) time-to-peak maps calculated from the time-intensity curve after injection of 40 mL of gadopentetate dimeglumine (f) TOF MR angiogram. Comment: Acute thrombosis of the left carotid artery. On T2-weighted SE image, only a faint increase in signal intensity in the insular cortex is seen. There is typical hyperintensity on DW image, with a decreased ADC value. There is an important perfusion deficit and only a limited penumbra (2).

View larger version (122K): [in this window] [in a new window] [Download PPT slide]   Figure 2b.  Acute infarction within the first 6 hours after stroke. (a) Fast T2-weighted SE image. (b, c) DW (trace) multishot echo-planar image and corresponding ADC map. (d, e) Perfusion-weighted multishot echo-planar imaging; (d) relative cerebral blood volume and (e) time-to-peak maps calculated from the time-intensity curve after injection of 40 mL of gadopentetate dimeglumine (f) TOF MR angiogram. Comment: Acute thrombosis of the left carotid artery. On T2-weighted SE image, only a faint increase in signal intensity in the insular cortex is seen. There is typical hyperintensity on DW image, with a decreased ADC value. There is an important perfusion deficit and only a limited penumbra (2).

View larger version (147K): [in this window] [in a new window] [Download PPT slide]   Figure 2c.  Acute infarction within the first 6 hours after stroke. (a) Fast T2-weighted SE image. (b, c) DW (trace) multishot echo-planar image and corresponding ADC map. (d, e) Perfusion-weighted multishot echo-planar imaging; (d) relative cerebral blood volume and (e) time-to-peak maps calculated from the time-intensity curve after injection of 40 mL of gadopentetate dimeglumine (f) TOF MR angiogram. Comment: Acute thrombosis of the left carotid artery. On T2-weighted SE image, only a faint increase in signal intensity in the insular cortex is seen. There is typical hyperintensity on DW image, with a decreased ADC value. There is an important perfusion deficit and only a limited penumbra (2).

View larger version (78K): [in this window] [in a new window] [Download PPT slide]   Figure 2d.  Acute infarction within the first 6 hours after stroke. (a) Fast T2-weighted SE image. (b, c) DW (trace) multishot echo-planar image and corresponding ADC map. (d, e) Perfusion-weighted multishot echo-planar imaging; (d) relative cerebral blood volume and (e) time-to-peak maps calculated from the time-intensity curve after injection of 40 mL of gadopentetate dimeglumine (f) TOF MR angiogram. Comment: Acute thrombosis of the left carotid artery. On T2-weighted SE image, only a faint increase in signal intensity in the insular cortex is seen. There is typical hyperintensity on DW image, with a decreased ADC value. There is an important perfusion deficit and only a limited penumbra (2).

View larger version (73K): [in this window] [in a new window] [Download PPT slide]   Figure 2e.  Acute infarction within the first 6 hours after stroke. (a) Fast T2-weighted SE image. (b, c) DW (trace) multishot echo-planar image and corresponding ADC map. (d, e) Perfusion-weighted multishot echo-planar imaging; (d) relative cerebral blood volume and (e) time-to-peak maps calculated from the time-intensity curve after injection of 40 mL of gadopentetate dimeglumine (f) TOF MR angiogram. Comment: Acute thrombosis of the left carotid artery. On T2-weighted SE image, only a faint increase in signal intensity in the insular cortex is seen. There is typical hyperintensity on DW image, with a decreased ADC value. There is an important perfusion deficit and only a limited penumbra (2).

View larger version (126K): [in this window] [in a new window] [Download PPT slide]   Figure 2f.  Acute infarction within the first 6 hours after stroke. (a) Fast T2-weighted SE image. (b, c) DW (trace) multishot echo-planar image and corresponding ADC map. (d, e) Perfusion-weighted multishot echo-planar imaging; (d) relative cerebral blood volume and (e) time-to-peak maps calculated from the time-intensity curve after injection of 40 mL of gadopentetate dimeglumine (f) TOF MR angiogram. Comment: Acute thrombosis of the left carotid artery. On T2-weighted SE image, only a faint increase in signal intensity in the insular cortex is seen. There is typical hyperintensity on DW image, with a decreased ADC value. There is an important perfusion deficit and only a limited penumbra (2).

View larger version (163K): [in this window] [in a new window] [Download PPT slide]   Figure 3a.  Venous infarction. (a) T2-weighted SE image and (b, c) DW echo-planar image (b) and corresponding ADC map (c).

View larger version (110K): [in this window] [in a new window] [Download PPT slide]   Figure 3b.  Venous infarction. (a) T2-weighted SE image and (b, c) DW echo-planar image (b) and corresponding ADC map (c).

View larger version (77K): [in this window] [in a new window] [Download PPT slide]   Figure 3c.  Venous infarction. (a) T2-weighted SE image and (b, c) DW echo-planar image (b) and corresponding ADC map (c).

• Clinical presentation (typically acute onset in arterial stroke; in venous sinus thrombosis, more insidious, frequently beginning with severe headache and/or seizures).
  
• Early hemorrhage, especially when close to the venous sinuses (unusual in acute ischemic stroke).
  
• With either or both of the above, perform MR or computed tomography (CT) venography
  

Differential Diagnosis with Cerebritis
The differential diagnosis of early-stage cerebral abscesses (cerebritis) (Fig 4) and acute infarction may be potentially problematic on conventional MR images or DW images. However, to our knowledge, only the early capsule stages of cerebral abscesses have been reported (53,54,58) on DW images.

View larger version (153K): [in this window] [in a new window] [Download PPT slide]   Figure 4a.  Early stage of cerebral abscess. (a) T2-weighted SE image, (b) contrast-enhanced T1-weighted SE image, and (c, d) DW echo-planar image (c) and corresponding ADC map (d). The signal intensity on the DW image and ADC map looks like that of an acute stroke. However, on the T2-weighted and enhanced T1-weighted images a fine capsule is readily recognized.

View larger version (143K): [in this window] [in a new window] [Download PPT slide]   Figure 4b.  Early stage of cerebral abscess. (a) T2-weighted SE image, (b) contrast-enhanced T1-weighted SE image, and (c, d) DW echo-planar image (c) and corresponding ADC map (d). The signal intensity on the DW image and ADC map looks like that of an acute stroke. However, on the T2-weighted and enhanced T1-weighted images a fine capsule is readily recognized.

View larger version (146K): [in this window] [in a new window] [Download PPT slide]   Figure 4c.  Early stage of cerebral abscess. (a) T2-weighted SE image, (b) contrast-enhanced T1-weighted SE image, and (c, d) DW echo-planar image (c) and corresponding ADC map (d). The signal intensity on the DW image and ADC map looks like that of an acute stroke. However, on the T2-weighted and enhanced T1-weighted images a fine capsule is readily recognized.

View larger version (99K): [in this window] [in a new window] [Download PPT slide]   Figure 4d.  Early stage of cerebral abscess. (a) T2-weighted SE image, (b) contrast-enhanced T1-weighted SE image, and (c, d) DW echo-planar image (c) and corresponding ADC map (d). The signal intensity on the DW image and ADC map looks like that of an acute stroke. However, on the T2-weighted and enhanced T1-weighted images a fine capsule is readily recognized.

• See the section on Inflammation: Abscess.
  

Background and Discussion
What Is the Evolution of Acute Stroke on DW Images and ADC Maps?

DW images.—The signal intensity of acute stroke on DW images increases during the 1st week after symptom onset and decreases thereafter; however, it remains hyperintense for a long period (up to 72 days in the study by Lansberg et al [3]). This pattern is most likely the result of two factors: initially to reduced diffusion and thereafter to increasing T2 (T2 "shine-through"). Because the DW imaging signal remains hyperintense for a long period, it is not ideal for estimating lesion age.

ADC values.—It is accepted that ADC values decline rapidly after the onset of ischemia and subsequently increase with the "flip-flop" from dark to bright 7-10 days later (4–8). This property may be used to differentiate the lesions older than 10 days from more acute ones (Table 1).

DW images and ADC maps show changes in ischemic brain tissue within hours after symptom onset, when no abnormalities are typically seen on conventional MR images (1,2,4–7,9,10).

Presumed CausesAcute ischemic lesions are characterized by high signal intensity on DW images and a low ADC (1). The ADC is believed to be low because of a shift of water within hypoxic brain parenchyma, from the extracellular to the intracellular compartment, where water diffusion is relatively restricted (1).

What are the Sensitivity and Specificity of DW images and ADC Maps in Acute Stroke?

The majority of studies report high sensitivity and specificity for DW images and ADC maps in the diagnosis of acute stroke (94%sensitivity and 100%specificity in the study by Lövblad et al [11] within the first 6 hours after stroke; 100%sensitivity and 100%specificity in the study by Gonzalez et al [12] in patients imaged within 6 hours of stroke symptom onset). In the study by Gonzalez et al (12), DW images indicated stroke in 14 patients, all of whom had a final diagnosis of acute stroke, and DW images were negative in eight patients, all of whom had a final clinical diagnosis other than stroke. On the other hand, there have been occasional reports of patients progressing to complete stroke after an initial negative DW imaging finding (13,14). The potential mechanism that may explain the lack of diffusion changes in the acute phase in these patients is that cerebral blood flow was at an intermediate level below the threshold for neuronal dysfunction (symptom onset) but above that of reduced diffusion (1).

Conclusions
The signal intensity of acute stroke on DW images increases during the 1st week after symptom onset and decreases thereafter, but signal remains hyperintense for a long period. The ADC values decline rapidly after the onset of ischemia and subsequently increase with the "flip-flop" from dark to bright 7-10 days later. This property may be used to differentiate the lesions older than 10 days from more acute ones. Most studies report high sensitivity and specificity for DW images and ADC maps in the diagnosis of acute stroke. There have been only occasional reports of patients progressing to complete stroke after an initial negative DW imaging finding. The differential diagnosis of arterial and venous stroke may be impossible with acute-stroke MR protocols (ie, including T2-weighted SE, FLAIR, DW and perfusion-weighted imaging, and MR arteriography). The clinical presentation and early hemorrhage, especially when near the venous sinuses, should prompt performance of MR or CT venography.

	Venous Infarction

Top Abstract Basic Physics of Diffusion... Acute Infarction Venous Infarction Tumors: Glioma Tumors: Metastases Tumors: Meningioma Tumors: Lymphoma Tumors: Epidermoid Cyst Inflammation: Abscess Inflammation: Granuloma Inflammation: Encephalitis Hemorrhage Multiple Sclerosis Creutzfeld-Jakob Disease Other Bright Lesions on... References

 
Typical Presentation on DW Images and ADC Maps
Diffusion findings in human venous infarction have so far been limited to conflicting case reports. The initial reports suggested increased to slightly decreased ADC values with hypo- to isointensity on DW images (15,16). These findings were explained by the presence of prominent vasogenic edema associated with mild cytotoxic edema. More recently, a larger series of venous infarctions with high signal intensity on DW images and low ADC values were reported (17–19). The findings were attributed to cytotoxic edema (Figs 5, 6).

View larger version (168K): [in this window] [in a new window] [Download PPT slide]   Figure 5a.  Acute venous infarction (superior sagittal sinus thrombosis) with high signal intensity on DW images and low ADC values. (a) Transverse T2-weighted fast SE image (5500/128 [repetition time/echo time]; 6-mm section thickness; three signals averaged; echo train length, 23; and 230 x 512 matrix). (b) Transverse T1-weighted SE image (550/14), 6-mm section thickness, three signals averaged, one echo, and 192 x 256). (c, d) Transverse DW image (x = sensitizing direction) (c) multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness) and corresponding ADC map (d). (e) Maximum-intensity projection of TOF venogram. These findings may be consistent with prominent cytotoxic edema. The differential diagnosis of hyperacute arterial stroke and venous stroke remains difficult on T2- or T1-weighed SE and DW images.

View larger version (96K): [in this window] [in a new window] [Download PPT slide]   Figure 5b.  Acute venous infarction (superior sagittal sinus thrombosis) with high signal intensity on DW images and low ADC values. (a) Transverse T2-weighted fast SE image (5500/128 [repetition time/echo time]; 6-mm section thickness; three signals averaged; echo train length, 23; and 230 x 512 matrix). (b) Transverse T1-weighted SE image (550/14), 6-mm section thickness, three signals averaged, one echo, and 192 x 256). (c, d) Transverse DW image (x = sensitizing direction) (c) multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness) and corresponding ADC map (d). (e) Maximum-intensity projection of TOF venogram. These findings may be consistent with prominent cytotoxic edema. The differential diagnosis of hyperacute arterial stroke and venous stroke remains difficult on T2- or T1-weighed SE and DW images.

View larger version (114K): [in this window] [in a new window] [Download PPT slide]   Figure 5c.  Acute venous infarction (superior sagittal sinus thrombosis) with high signal intensity on DW images and low ADC values. (a) Transverse T2-weighted fast SE image (5500/128 [repetition time/echo time]; 6-mm section thickness; three signals averaged; echo train length, 23; and 230 x 512 matrix). (b) Transverse T1-weighted SE image (550/14), 6-mm section thickness, three signals averaged, one echo, and 192 x 256). (c, d) Transverse DW image (x = sensitizing direction) (c) multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness) and corresponding ADC map (d). (e) Maximum-intensity projection of TOF venogram. These findings may be consistent with prominent cytotoxic edema. The differential diagnosis of hyperacute arterial stroke and venous stroke remains difficult on T2- or T1-weighed SE and DW images.

View larger version (76K): [in this window] [in a new window] [Download PPT slide]   Figure 5d.  Acute venous infarction (superior sagittal sinus thrombosis) with high signal intensity on DW images and low ADC values. (a) Transverse T2-weighted fast SE image (5500/128 [repetition time/echo time]; 6-mm section thickness; three signals averaged; echo train length, 23; and 230 x 512 matrix). (b) Transverse T1-weighted SE image (550/14), 6-mm section thickness, three signals averaged, one echo, and 192 x 256). (c, d) Transverse DW image (x = sensitizing direction) (c) multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness) and corresponding ADC map (d). (e) Maximum-intensity projection of TOF venogram. These findings may be consistent with prominent cytotoxic edema. The differential diagnosis of hyperacute arterial stroke and venous stroke remains difficult on T2- or T1-weighed SE and DW images.

View larger version (117K): [in this window] [in a new window] [Download PPT slide]   Figure 5e.  Acute venous infarction (superior sagittal sinus thrombosis) with high signal intensity on DW images and low ADC values. (a) Transverse T2-weighted fast SE image (5500/128 [repetition time/echo time]; 6-mm section thickness; three signals averaged; echo train length, 23; and 230 x 512 matrix). (b) Transverse T1-weighted SE image (550/14), 6-mm section thickness, three signals averaged, one echo, and 192 x 256). (c, d) Transverse DW image (x = sensitizing direction) (c) multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness) and corresponding ADC map (d). (e) Maximum-intensity projection of TOF venogram. These findings may be consistent with prominent cytotoxic edema. The differential diagnosis of hyperacute arterial stroke and venous stroke remains difficult on T2- or T1-weighed SE and DW images.

View larger version (156K): [in this window] [in a new window] [Download PPT slide]   Figure 6a.  Acute venous infarction with low signal on DW images and increased ADC values (left lateral sinus thrombosis). (a, b) Transverse T2-weighted (a) and T1-weighted (b) SE images. (c, d) Transverse DW (trace) multishot echo-planar image (c) and corresponding ADC map (d). (e) Maximum-intensity projection of phase-contrast venography (20 cm/sec). These findings may be consistent with prominent vasogenic edema.

View larger version (145K): [in this window] [in a new window] [Download PPT slide]   Figure 6b.  Acute venous infarction with low signal on DW images and increased ADC values (left lateral sinus thrombosis). (a, b) Transverse T2-weighted (a) and T1-weighted (b) SE images. (c, d) Transverse DW (trace) multishot echo-planar image (c) and corresponding ADC map (d). (e) Maximum-intensity projection of phase-contrast venography (20 cm/sec). These findings may be consistent with prominent vasogenic edema.

View larger version (127K): [in this window] [in a new window] [Download PPT slide]   Figure 6c.  Acute venous infarction with low signal on DW images and increased ADC values (left lateral sinus thrombosis). (a, b) Transverse T2-weighted (a) and T1-weighted (b) SE images. (c, d) Transverse DW (trace) multishot echo-planar image (c) and corresponding ADC map (d). (e) Maximum-intensity projection of phase-contrast venography (20 cm/sec). These findings may be consistent with prominent vasogenic edema.

View larger version (146K): [in this window] [in a new window] [Download PPT slide]   Figure 6d.  Acute venous infarction with low signal on DW images and increased ADC values (left lateral sinus thrombosis). (a, b) Transverse T2-weighted (a) and T1-weighted (b) SE images. (c, d) Transverse DW (trace) multishot echo-planar image (c) and corresponding ADC map (d). (e) Maximum-intensity projection of phase-contrast venography (20 cm/sec). These findings may be consistent with prominent vasogenic edema.

For more information, see the section on Acute Infarction.

Background and Discussion
Imaging

The diffusion findings in human cerebral venous infarction remain controversial. Initial reports suggested increased to slightly decreased ADC values with hypo- to isointensity on DW images (15,16). These findings were explained by the presence of prominent vasogenic edema associated with mild cytotoxic edema.

In 1998, Corvol et al (15) reported a case of an extensive thrombosis of the superior sagittal sinus and the left lateral sinus. There was a large frontoparietal hyperintensity on FLAIR images and only a discrete hyperintensity on DW images, with a slight decrease in ADC values (0.53 x 10^-3 mm²/sec compared with 0.61 x 10^-3 mm²/sec in the contralateral hemisphere). These findings were explained by prominent vasogenic edema associated with mild cytotoxic edema.

In 1999, Keller et al (16) reported the findings in a case of a deep cerebral venous thrombosis with extensive hyperintensities in the basal ganglia on T2-weighted images and hypointensities on DW images, with increased ADC values (1.1-1.6 x 10^-3 mm²/sec). These findings were explained by the presence of vasogenic edema. The patient was treated with intravenous heparin, with total clinical recovery and no parenchymal defects at follow-up MR examinations.

More recently, a larger series of cerebral venous infarctions with high signal intensity on DW images and low ADC values were reported (17–19). The findings were attributed to cytotoxic edema.

Manzione et al (17) reported a case of a superior sagittal sinus thrombosis and a right transverse sinus thrombosis with a frontal hyperintensity on T2-weighted images and two more extensive hyperintensities on DW images, associated with an area of severe (0.2 x 10^-3 mm²/sec) and an area of moderate (0.3 x 10^-3 mm²/sec) reduction in ADC values. The lesion with a severe reduction in ADC values was associated with a small residual lesion at follow-up MR examination, while the area with a moderate reduction in ADC values reversed completely.

Forbes et al (18) studied 12 patients with acute cerebral venous thrombosis. Ten regions of cerebral venous infarction were detected in seven patients, all showing T2 hyperintensity. Two of these regions were predominantly hemorrhagic and did not display diffusion hyperintensity. The remaining eight regions displayed diffusion hyperintensity associated with a decreased ADC.

In a case of a superior sagittal sinus thrombosis reported by Peeters et al (19), the faint hyperintensity on T2-weighted SE and FLAIR images was associated with pronounced hyperintensity on DW images and an important decrease in ADC values in the range of 0.34–0.46 x 10^-3 mm²/sec, compared with 0.68 x 10^-3 mm²/sec in the contralateral hemisphere.

Presumed Causes of Low and High Signal Intensity on DW Images

The pathophysiologic mechanisms that lead to cerebral venous infarction remain controversial. Traditional models hold that retrograde venous pressure causes a breakdown of the blood-brain barrier, with leakage of fluid (vasogenic edema) and hemorrhage into the extracellular space (20).

Alternatively, a pathway from venous obstruction to infarction has been proposed wherein retrograde venous pressure decreases cerebral blood flow, causing tissue damage in a manner similar to that of arterial infarction (21,22). Furthermore, early decreases in ADC values have been shown in animal models of cerebral venous infarction, implying the presence of cytotoxic edema (22).

In our opinion, a coherent model of the pathogenesis of cerebral venous infarction should combine these two explanations. The initial event in venous infarction is the rise is venous pressure associated with disruption of the capillary tight junctions; this produces an increase in extracellular water (vasogenic edema). These lesions are completely reversible, provided there is successful venous thrombolysis, as reported (15,16). An increase in intracellular water follows (cytotoxic edema), resulting in restriction of water diffusion and hyperintensity on DW images (17–19). The mechanism may be energy failure with loss of sodium-potassium pump activity, as in arterial stroke. The reduction in cerebral blood flow may be an important factor in this process. However, in contrast to arterial stroke, the "bright" lesions on DW images in venous infarction might be more susceptible to complete recovery if successfully treated, as we reported (19). We know from studies with xenon CT in acute human stroke that cerebral blood flow of 6 mL/100g/min will produce irreversible infarction, while the ischemic penumbra with flow values of 7-20 mL/100g/min may be salvaged after restoration of normal flow (23). In venous infarction, hypoperfusion develops progressively. We postulate that it probably seldom falls under the threshold of approximately 6 mL/100g/min, since perfusion of the affected brain tissue might still be possible at lower flow rates if the blood drains through collateral pathways (22). The swollen cells might be functionally but not irreversibly damaged and therefore have a potential for recovery (24).

Conclusions
The differential diagnosis of arterial and venous stroke may be impossible with acute-stroke MR protocols. The diagnosis of venous sinus thrombosis during the first 7 days after the event is not always straightforward with conventional T1- and T2-weighted sequences. Important perfusion abnormalities have also been reported in venous stroke, and normal findings at MR arteriography do not exclude arterial stroke (eg, small branches or early spontaneous recanalization).

The diffusion findings in human cerebral venous infarction remain controversial. Initial reports suggested increased to slightly decreased ADC values with hypo- to isointensity on DW images (15,16). These findings were explained by the presence of prominent vasogenic edema associated with mild cytotoxic edema. More recently, a larger series of cerebral venous infarctions with high signal intensity on DW images and low ADC values have been reported (17–19), and the findings were attributed to cytotoxic edema. The pathophysiologic mechanisms that lead to cerebral venous infarction also remain controversial.

	Tumors: Glioma

Top Abstract Basic Physics of Diffusion... Acute Infarction Venous Infarction Tumors: Glioma Tumors: Metastases Tumors: Meningioma Tumors: Lymphoma Tumors: Epidermoid Cyst Inflammation: Abscess Inflammation: Granuloma Inflammation: Encephalitis Hemorrhage Multiple Sclerosis Creutzfeld-Jakob Disease Other Bright Lesions on... References

 
Typical Presentation on DW Images and ADC Maps
The signal intensity of gliomas on DW images is variable (hyper-, iso-, or hypointense) (25,26). Occasionally the gliomas are hyperintense on DW images and show reduced ADC values (suggests reduced volume of extracellular space) or not reduced ADC values (suggests T2 "shine-through" effect) (Fig 7).

View larger version (161K): [in this window] [in a new window] [Download PPT slide]   Figure 7a.  Glioblastoma multiforme. (a) Transverse T2-weighted fast SE image (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512). (b) Transverse T1-weighted nonenhanced SE image (520/14; two signals averaged; 6-mm section thickness; matrix, 179 x 256). (c) Transverse T1-weighted contrast-enhanced SE image (520/14; two signals averaged; 6-mm section thickness; matrix, 179 x 256). (d-f) (d) Transverse multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness), (e) corresponding DW echo-planar image (sensitizing direction = x), and (f) corresponding ADC map. The high signal intensity of cerebrospinal fluid on the multishot echo-planar image (d) is suppressed on the DW echo-planar image (e). The nonnecrotic components of glioblastoma are slightly hyperintense on the DW echo-planar image (T2 shine-through effect). On DW images (e), the peritumoral vasogenic edema is isointense to the white matter because the effect of increased diffusion (dark) is compensated for by the increased T2 values of edema (bright). The peritumoral edema, cerebrospinal fluid, and necrotic component of the tumor are hyperintense (high diffusion) on the ADC map.

View larger version (123K): [in this window] [in a new window] [Download PPT slide]   Figure 7b.  Glioblastoma multiforme. (a) Transverse T2-weighted fast SE image (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512). (b) Transverse T1-weighted nonenhanced SE image (520/14; two signals averaged; 6-mm section thickness; matrix, 179 x 256). (c) Transverse T1-weighted contrast-enhanced SE image (520/14; two signals averaged; 6-mm section thickness; matrix, 179 x 256). (d-f) (d) Transverse multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness), (e) corresponding DW echo-planar image (sensitizing direction = x), and (f) corresponding ADC map. The high signal intensity of cerebrospinal fluid on the multishot echo-planar image (d) is suppressed on the DW echo-planar image (e). The nonnecrotic components of glioblastoma are slightly hyperintense on the DW echo-planar image (T2 shine-through effect). On DW images (e), the peritumoral vasogenic edema is isointense to the white matter because the effect of increased diffusion (dark) is compensated for by the increased T2 values of edema (bright). The peritumoral edema, cerebrospinal fluid, and necrotic component of the tumor are hyperintense (high diffusion) on the ADC map.

View larger version (105K): [in this window] [in a new window] [Download PPT slide]   Figure 7c.  Glioblastoma multiforme. (a) Transverse T2-weighted fast SE image (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512). (b) Transverse T1-weighted nonenhanced SE image (520/14; two signals averaged; 6-mm section thickness; matrix, 179 x 256). (c) Transverse T1-weighted contrast-enhanced SE image (520/14; two signals averaged; 6-mm section thickness; matrix, 179 x 256). (d-f) (d) Transverse multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness), (e) corresponding DW echo-planar image (sensitizing direction = x), and (f) corresponding ADC map. The high signal intensity of cerebrospinal fluid on the multishot echo-planar image (d) is suppressed on the DW echo-planar image (e). The nonnecrotic components of glioblastoma are slightly hyperintense on the DW echo-planar image (T2 shine-through effect). On DW images (e), the peritumoral vasogenic edema is isointense to the white matter because the effect of increased diffusion (dark) is compensated for by the increased T2 values of edema (bright). The peritumoral edema, cerebrospinal fluid, and necrotic component of the tumor are hyperintense (high diffusion) on the ADC map.

View larger version (102K): [in this window] [in a new window] [Download PPT slide]   Figure 7d.  Glioblastoma multiforme. (a) Transverse T2-weighted fast SE image (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512). (b) Transverse T1-weighted nonenhanced SE image (520/14; two signals averaged; 6-mm section thickness; matrix, 179 x 256). (c) Transverse T1-weighted contrast-enhanced SE image (520/14; two signals averaged; 6-mm section thickness; matrix, 179 x 256). (d-f) (d) Transverse multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness), (e) corresponding DW echo-planar image (sensitizing direction = x), and (f) corresponding ADC map. The high signal intensity of cerebrospinal fluid on the multishot echo-planar image (d) is suppressed on the DW echo-planar image (e). The nonnecrotic components of glioblastoma are slightly hyperintense on the DW echo-planar image (T2 shine-through effect). On DW images (e), the peritumoral vasogenic edema is isointense to the white matter because the effect of increased diffusion (dark) is compensated for by the increased T2 values of edema (bright). The peritumoral edema, cerebrospinal fluid, and necrotic component of the tumor are hyperintense (high diffusion) on the ADC map.

View larger version (112K): [in this window] [in a new window] [Download PPT slide]   Figure 7e.  Glioblastoma multiforme. (a) Transverse T2-weighted fast SE image (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512). (b) Transverse T1-weighted nonenhanced SE image (520/14; two signals averaged; 6-mm section thickness; matrix, 179 x 256). (c) Transverse T1-weighted contrast-enhanced SE image (520/14; two signals averaged; 6-mm section thickness; matrix, 179 x 256). (d-f) (d) Transverse multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness), (e) corresponding DW echo-planar image (sensitizing direction = x), and (f) corresponding ADC map. The high signal intensity of cerebrospinal fluid on the multishot echo-planar image (d) is suppressed on the DW echo-planar image (e). The nonnecrotic components of glioblastoma are slightly hyperintense on the DW echo-planar image (T2 shine-through effect). On DW images (e), the peritumoral vasogenic edema is isointense to the white matter because the effect of increased diffusion (dark) is compensated for by the increased T2 values of edema (bright). The peritumoral edema, cerebrospinal fluid, and necrotic component of the tumor are hyperintense (high diffusion) on the ADC map.

View larger version (101K): [in this window] [in a new window] [Download PPT slide]   Figure 7f.  Glioblastoma multiforme. (a) Transverse T2-weighted fast SE image (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512). (b) Transverse T1-weighted nonenhanced SE image (520/14; two signals averaged; 6-mm section thickness; matrix, 179 x 256). (c) Transverse T1-weighted contrast-enhanced SE image (520/14; two signals averaged; 6-mm section thickness; matrix, 179 x 256). (d-f) (d) Transverse multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness), (e) corresponding DW echo-planar image (sensitizing direction = x), and (f) corresponding ADC map. The high signal intensity of cerebrospinal fluid on the multishot echo-planar image (d) is suppressed on the DW echo-planar image (e). The nonnecrotic components of glioblastoma are slightly hyperintense on the DW echo-planar image (T2 shine-through effect). On DW images (e), the peritumoral vasogenic edema is isointense to the white matter because the effect of increased diffusion (dark) is compensated for by the increased T2 values of edema (bright). The peritumoral edema, cerebrospinal fluid, and necrotic component of the tumor are hyperintense (high diffusion) on the ADC map.

For more information, see the section on Inflammation: Abscess.

Background and Discussion
Signal Intensity of the Solid Portion of Gliomas on DW Images and ADC Maps

The signal intensity of gliomas on DW images is variable (hyper-, iso-, or hypointense), and a subtle hyperintensity is a common nonspecific finding (1,11) (Table 2). The reported ADC values are in the range of 0.82 ± 0.13 to 1.14 ± 0.18 (x 10^-3 mm²/sec) (1–11). Tumor cellularity is probably a major determinant of ADC values of brain tumors, although probably not the only one (1,3,11).

ADC values cannot be used in individual cases to differentiate glioma types reliably (the ADCs of patients with grade II astrocytoma and glioblastoma overlap) (25,26,28,29). However, in the study of Kono et al (25), the combination of routine image interpretation and ADC values had a higher predictive value. In the study of Gauvain et al (28), there was a clear distinction between the low-grade gliomas and the embryonal tumors (the ADC values for low-grade gliomas were 1.33 x 10^-3 mm²/sec ± 0.21 (range, 1.132–1.60), for nonembryonal high-grade tumors the ADC values were 1.22 x 10^-3 mm²/sec ± 0.09 (range, 1.128–1.303) and for the group of embryonal tumors (primitive neuroectodermal tumor, medulloblastoma, malignant teratoid-rhabdoid tumor) the ADC values were 0.72 x 10^-3 mm²/sec ± 0.20 (range, 0.538–0.974).

Can the DW Images and/or ADC Maps Differentiate between Glioma and Peritumoral Edema?

The majority of recent studies report that DW images and/or ADC maps cannot distinguish neoplastic cell infiltration from peritumoral edema in patients with malignant glioma (25,26,28,29). In 1995, Tien et al (30) could distinguish areas of peritumoral neoplastic cell infiltration from predominantly peritumoral edema when abnormalities were located in the white matter aligned in the direction of the DW gradient. However, Recent findings do not support the hypothesis that peritumoral neoplastic cell infiltration can be depicted by means of ADCs or ADC maps (25,26,28,29).

Conclusions
The signal intensity of gliomas on DW images is variable (hyper-, iso-, or hypointense) (25,26). Occasionally, gliomas are hyperintense on DW images and show reduced ADC values (suggests reduced volume of extracellular space) or not reduced ADC values (suggests T2 shine-through effect). Tumor cellularity is probably a major determinant of ADC values of brain tumors. ADC values cannot be used in individual cases to differentiate glioma types reliably. DW images and/or ADC maps cannot distinguish neoplastic cell infiltration from peritumoral edema in patients with malignant glioma (25,26,28,29).

	Tumors: Metastases

Top Abstract Basic Physics of Diffusion... Acute Infarction Venous Infarction Tumors: Glioma Tumors: Metastases Tumors: Meningioma Tumors: Lymphoma Tumors: Epidermoid Cyst Inflammation: Abscess Inflammation: Granuloma Inflammation: Encephalitis Hemorrhage Multiple Sclerosis Creutzfeld-Jakob Disease Other Bright Lesions on... References

 
Typical Presentation on DW Images and ADC Maps
The reported cases of metastases were isointense to slightly hyperintense on DW images, and the calculated ADC values were in the range 0.82–1.24 x 10^-3 mm²/sec (26).

In our experience, the signal intensity of nonnecrotic components of metastases on DW images is variable (generally iso- or hypointense; occasionally hyperintense). The necrotic components of metastases show a marked signal suppression on DW MR images and increased ADC values (31). The increased signal intensity on DW images and a low ADC value are unusual but possible (32) (Figs 8, 9).

View larger version (164K): [in this window] [in a new window] [Download PPT slide]   Figure 8a.  Multiple metastases. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (trace) images and (e) corresponding ADC map.

View larger version (130K): [in this window] [in a new window] [Download PPT slide]   Figure 8b.  Multiple metastases. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (trace) images and (e) corresponding ADC map.

View larger version (129K): [in this window] [in a new window] [Download PPT slide]   Figure 8c.  Multiple metastases. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (trace) images and (e) corresponding ADC map.

View larger version (109K): [in this window] [in a new window] [Download PPT slide]   Figure 8d.  Multiple metastases. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (trace) images and (e) corresponding ADC map.

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 8e.  Multiple metastases. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (trace) images and (e) corresponding ADC map.

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   Figure 9a.  Multiple metastases in same patient as in Figure 8, at a different level. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW images (trace) and (e) corresponding ADC map. (f) Magnification of e. The ADC value for region of interest 1 (solid component of metastasis) is 0.76 x 10-3 mm2/sec; for region of interest 2 (contralateral gray and white matter), the ADC value is 0.73 x 10-3 mm2/sec.

View larger version (111K): [in this window] [in a new window] [Download PPT slide]   Figure 9b.  Multiple metastases in same patient as in Figure 8, at a different level. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW images (trace) and (e) corresponding ADC map. (f) Magnification of e. The ADC value for region of interest 1 (solid component of metastasis) is 0.76 x 10-3 mm2/sec; for region of interest 2 (contralateral gray and white matter), the ADC value is 0.73 x 10-3 mm2/sec.

View larger version (110K): [in this window] [in a new window] [Download PPT slide]   Figure 9c.  Multiple metastases in same patient as in Figure 8, at a different level. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW images (trace) and (e) corresponding ADC map. (f) Magnification of e. The ADC value for region of interest 1 (solid component of metastasis) is 0.76 x 10-3 mm2/sec; for region of interest 2 (contralateral gray and white matter), the ADC value is 0.73 x 10-3 mm2/sec.

View larger version (86K): [in this window] [in a new window] [Download PPT slide]   Figure 9d.  Multiple metastases in same patient as in Figure 8, at a different level. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW images (trace) and (e) corresponding ADC map. (f) Magnification of e. The ADC value for region of interest 1 (solid component of metastasis) is 0.76 x 10-3 mm2/sec; for region of interest 2 (contralateral gray and white matter), the ADC value is 0.73 x 10-3 mm2/sec.

View larger version (89K): [in this window] [in a new window] [Download PPT slide]   Figure 9e.  Multiple metastases in same patient as in Figure 8, at a different level. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW images (trace) and (e) corresponding ADC map. (f) Magnification of e. The ADC value for region of interest 1 (solid component of metastasis) is 0.76 x 10-3 mm2/sec; for region of interest 2 (contralateral gray and white matter), the ADC value is 0.73 x 10-3 mm2/sec.

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   Figure 9f.  Multiple metastases in same patient as in Figure 8, at a different level. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW images (trace) and (e) corresponding ADC map. (f) Magnification of e. The ADC value for region of interest 1 (solid component of metastasis) is 0.76 x 10-3 mm2/sec; for region of interest 2 (contralateral gray and white matter), the ADC value is 0.73 x 10-3 mm2/sec.

Differential Diagnosis of Ring-enhancing Cerebral Masses
The differential diagnosis of intracerebral necrotic metastases (Fig 10) and cerebral abscesses is frequently impossible on conventional MR images. DW imaging is a valuable diagnostic test in cases of cerebral ring-enhancing masses.

View larger version (150K): [in this window] [in a new window] [Download PPT slide]   Figure 10a.  Cerebral metastasis. (a) T2-weighted fast SE, (b) contrast-enhanced T1-weighted SE, and (c) DW (sensitizing direction = z) multishot echo-planar (800/123, five signals averaged, 6-mm section thickness images and (d) corresponding ADC map.

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 10b.  Cerebral metastasis. (a) T2-weighted fast SE, (b) contrast-enhanced T1-weighted SE, and (c) DW (sensitizing direction = z) multishot echo-planar (800/123, five signals averaged, 6-mm section thickness images and (d) corresponding ADC map.

View larger version (158K): [in this window] [in a new window] [Download PPT slide]   Figure 10c.  Cerebral metastasis. (a) T2-weighted fast SE, (b) contrast-enhanced T1-weighted SE, and (c) DW (sensitizing direction = z) multishot echo-planar (800/123, five signals averaged, 6-mm section thickness images and (d) corresponding ADC map.

View larger version (110K): [in this window] [in a new window] [Download PPT slide]   Figure 10d.  Cerebral metastasis. (a) T2-weighted fast SE, (b) contrast-enhanced T1-weighted SE, and (c) DW (sensitizing direction = z) multishot echo-planar (800/123, five signals averaged, 6-mm section thickness images and (d) corresponding ADC map.

For more information, see the section on Inflammation: Abscess

Background and Discussion
DW imaging of cerebral metastases has received only limited attention. In the reported cases, the solid components of cerebral metastases were isointense to slightly hyperintense on DW images and the calculated ADC values were in the range 0.82–1.24 x 10^-3 mm²/sec (26).

In our experience, the signal intensity of nonnecrotic components of metastases on DW images is variable (generally iso- or hypointense, occasionally hyperintense).

The necrotic components of cerebral metastases show a marked signal suppression on DW images and increased ADC values (mean value of 2.62 x 10^-3 mm²/sec [n = 7] in the report of Krabbe et al [31]). The increased signal intensity on DW images and a low ADC value are unusual but possible. Tung et al reported two metastases, both squamous cell carcinomas, with markedly increased signal intensity on DW images and a low ADC value (32). However, this presentation was unusual. In the same report, only five of 30 rim-enhanced masses had high signal intensity on DW images and low ADC values; two of these five cases were brain abscesses, two were the metastases from lung squamous cell carcinoma, and one was radiation necrosis (32). In a report by Hartmann et al (33), only one metastasis of eight had high signal intensity on DW images and low ADC values (Fig 11).

View larger version (150K): [in this window] [in a new window] [Download PPT slide]   Figure 11a.  Cerebral metastasis with increased signal intensity on DW images. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (trace) images and (e) corresponding ADC map. Old hemorrhagic content was found at surgery.

View larger version (98K): [in this window] [in a new window] [Download PPT slide]   Figure 11b.  Cerebral metastasis with increased signal intensity on DW images. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (trace) images and (e) corresponding ADC map. Old hemorrhagic content was found at surgery.

View larger version (104K): [in this window] [in a new window] [Download PPT slide]   Figure 11c.  Cerebral metastasis with increased signal intensity on DW images. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (trace) images and (e) corresponding ADC map. Old hemorrhagic content was found at surgery.

View larger version (143K): [in this window] [in a new window] [Download PPT slide]   Figure 11d.  Cerebral metastasis with increased signal intensity on DW images. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (trace) images and (e) corresponding ADC map. Old hemorrhagic content was found at surgery.

View larger version (118K): [in this window] [in a new window] [Download PPT slide]   Figure 11e.  Cerebral metastasis with increased signal intensity on DW images. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (trace) images and (e) corresponding ADC map. Old hemorrhagic content was found at surgery.

Conclusions
In our experience, the signal intensity of nonnecrotic components of metastases on DW images is variable (generally iso- or hypointense, occasionally hyperintense). The necrotic components of metastases show a marked signal suppression on DW images and increased ADC values (may be related to increased free water). Increased signal intensity on DW images and a low ADC value are unusual but possible (may be related to the presence of extracellular methemoglobin and/or increased viscosity).

	Tumors: Meningioma

Top Abstract Basic Physics of Diffusion... Acute Infarction Venous Infarction Tumors: Glioma Tumors: Metastases Tumors: Meningioma Tumors: Lymphoma Tumors: Epidermoid Cyst Inflammation: Abscess Inflammation: Granuloma Inflammation: Encephalitis Hemorrhage Multiple Sclerosis Creutzfeld-Jakob Disease Other Bright Lesions on... References

 
Typical presentation on DW images and ADC maps
The signal intensity of meningiomas on DW images is variable (hyper-, iso-, or hypointense) (26,34). Most benign meningiomas are isointense on DW images and ADC maps (Figs 12, 13) (26,34). Only 23%of benign meningiomas (three of 13) were slightly hyperintense in the study of Filippi et al (34). In the same study, four malignant meningiomas had markedly increased signal intensity on DW images, decreased signal intensity on ADC maps, and low ADC values (34).

View larger version (177K): [in this window] [in a new window] [Download PPT slide]   Figure 12a.  Benign meningioma. (a) T2-weighted SE, (b) T1-weighted SE, and (c) multishot (800/123, one signal acquired, 6-mm section thickness) DW echo-planar (sensitizing direction = z) images and (d) corresponding ADC map. (e, f) Contrast-enhanced T1-weighted SE images acquired in the (e) transverse and (f) coronal planes. This meningioma is hyperintense on the DW echo-planar image and iso- to hypointense on the corresponding ADC map. The ADC values were in the range 0.39-0.46 x 10-3 mm2/sec (0.61-0.63 x 10-3 mm2/sec for the contralateral white and gray matter).

View larger version (154K): [in this window] [in a new window] [Download PPT slide]   Figure 12b.  Benign meningioma. (a) T2-weighted SE, (b) T1-weighted SE, and (c) multishot (800/123, one signal acquired, 6-mm section thickness) DW echo-planar (sensitizing direction = z) images and (d) corresponding ADC map. (e, f) Contrast-enhanced T1-weighted SE images acquired in the (e) transverse and (f) coronal planes. This meningioma is hyperintense on the DW echo-planar image and iso- to hypointense on the corresponding ADC map. The ADC values were in the range 0.39-0.46 x 10-3 mm2/sec (0.61-0.63 x 10-3 mm2/sec for the contralateral white and gray matter).

View larger version (168K): [in this window] [in a new window] [Download PPT slide]   Figure 12c.  Benign meningioma. (a) T2-weighted SE, (b) T1-weighted SE, and (c) multishot (800/123, one signal acquired, 6-mm section thickness) DW echo-planar (sensitizing direction = z) images and (d) corresponding ADC map. (e, f) Contrast-enhanced T1-weighted SE images acquired in the (e) transverse and (f) coronal planes. This meningioma is hyperintense on the DW echo-planar image and iso- to hypointense on the corresponding ADC map. The ADC values were in the range 0.39-0.46 x 10-3 mm2/sec (0.61-0.63 x 10-3 mm2/sec for the contralateral white and gray matter).

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 12d.  Benign meningioma. (a) T2-weighted SE, (b) T1-weighted SE, and (c) multishot (800/123, one signal acquired, 6-mm section thickness) DW echo-planar (sensitizing direction = z) images and (d) corresponding ADC map. (e, f) Contrast-enhanced T1-weighted SE images acquired in the (e) transverse and (f) coronal planes. This meningioma is hyperintense on the DW echo-planar image and iso- to hypointense on the corresponding ADC map. The ADC values were in the range 0.39-0.46 x 10-3 mm2/sec (0.61-0.63 x 10-3 mm2/sec for the contralateral white and gray matter).

View larger version (152K): [in this window] [in a new window] [Download PPT slide]   Figure 12e.  Benign meningioma. (a) T2-weighted SE, (b) T1-weighted SE, and (c) multishot (800/123, one signal acquired, 6-mm section thickness) DW echo-planar (sensitizing direction = z) images and (d) corresponding ADC map. (e, f) Contrast-enhanced T1-weighted SE images acquired in the (e) transverse and (f) coronal planes. This meningioma is hyperintense on the DW echo-planar image and iso- to hypointense on the corresponding ADC map. The ADC values were in the range 0.39-0.46 x 10-3 mm2/sec (0.61-0.63 x 10-3 mm2/sec for the contralateral white and gray matter).

View larger version (138K): [in this window] [in a new window] [Download PPT slide]   Figure 12f.  Benign meningioma. (a) T2-weighted SE, (b) T1-weighted SE, and (c) multishot (800/123, one signal acquired, 6-mm section thickness) DW echo-planar (sensitizing direction = z) images and (d) corresponding ADC map. (e, f) Contrast-enhanced T1-weighted SE images acquired in the (e) transverse and (f) coronal planes. This meningioma is hyperintense on the DW echo-planar image and iso- to hypointense on the corresponding ADC map. The ADC values were in the range 0.39-0.46 x 10-3 mm2/sec (0.61-0.63 x 10-3 mm2/sec for the contralateral white and gray matter).

View larger version (67K): [in this window] [in a new window] [Download PPT slide]   Figure 13a.  Calcified meningioma with cortical infarction. (a) Nonenhanced CT, (b) T2-weighted SE, (c) contrast-enhanced T1-weighted SE, and (d) multishot (800/123, one signal acquired, 6-mm section thickness) DW echo-planar (sensitizing direction = z) images and (e) corresponding ADC map. This calcified meningioma was an incidental finding. It is hypointense on the DW echo-planar image and on the corresponding ADC map. The ADC values were in the range 0.21-0.75 x 10-3 mm2/sec.

View larger version (156K): [in this window] [in a new window] [Download PPT slide]   Figure 13b.  Calcified meningioma with cortical infarction. (a) Nonenhanced CT, (b) T2-weighted SE, (c) contrast-enhanced T1-weighted SE, and (d) multishot (800/123, one signal acquired, 6-mm section thickness) DW echo-planar (sensitizing direction = z) images and (e) corresponding ADC map. This calcified meningioma was an incidental finding. It is hypointense on the DW echo-planar image and on the corresponding ADC map. The ADC values were in the range 0.21-0.75 x 10-3 mm2/sec.

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 13c.  Calcified meningioma with cortical infarction. (a) Nonenhanced CT, (b) T2-weighted SE, (c) contrast-enhanced T1-weighted SE, and (d) multishot (800/123, one signal acquired, 6-mm section thickness) DW echo-planar (sensitizing direction = z) images and (e) corresponding ADC map. This calcified meningioma was an incidental finding. It is hypointense on the DW echo-planar image and on the corresponding ADC map. The ADC values were in the range 0.21-0.75 x 10-3 mm2/sec.

View larger version (153K): [in this window] [in a new window] [Download PPT slide]   Figure 13d.  Calcified meningioma with cortical infarction. (a) Nonenhanced CT, (b) T2-weighted SE, (c) contrast-enhanced T1-weighted SE, and (d) multishot (800/123, one signal acquired, 6-mm section thickness) DW echo-planar (sensitizing direction = z) images and (e) corresponding ADC map. This calcified meningioma was an incidental finding. It is hypointense on the DW echo-planar image and on the corresponding ADC map. The ADC values were in the range 0.21-0.75 x 10-3 mm2/sec.

View larger version (112K): [in this window] [in a new window] [Download PPT slide]   Figure 13e.  Calcified meningioma with cortical infarction. (a) Nonenhanced CT, (b) T2-weighted SE, (c) contrast-enhanced T1-weighted SE, and (d) multishot (800/123, one signal acquired, 6-mm section thickness) DW echo-planar (sensitizing direction = z) images and (e) corresponding ADC map. This calcified meningioma was an incidental finding. It is hypointense on the DW echo-planar image and on the corresponding ADC map. The ADC values were in the range 0.21-0.75 x 10-3 mm2/sec.

Conclusions
The signal intensity of meningiomas on DW images is variable (hyper-, iso-, or hypointense) (26,34). Most benign meningiomas are isointense on DW images and ADC maps (26,34). Only 23%of benign meningiomas were slightly hyperintense (three of 13) in the study of Filippi et al (34). On average, these meningiomas had an elevation in the ADC value. High signal intensity on DW images and reduced ADC values (average, 0.53 x 10^-3 mm²/sec ± 0.12; range, 0.40–0.69 x 10^-3 mm²/sec) suggest malignant meningioma (34). In our experience, however, benign meningiomas may also show high signal intensity on DW images and reduced ADC values.

	Tumors: Lymphoma

Top Abstract Basic Physics of Diffusion... Acute Infarction Venous Infarction Tumors: Glioma Tumors: Metastases Tumors: Meningioma Tumors: Lymphoma Tumors: Epidermoid Cyst Inflammation: Abscess Inflammation: Granuloma Inflammation: Encephalitis Hemorrhage Multiple Sclerosis Creutzfeld-Jakob Disease Other Bright Lesions on... References

 
Typical Presentation on DW images and ADC Maps
The enhancing components of lymphomas are generally hyperintense on DW images (Fig 14).

View larger version (160K): [in this window] [in a new window] [Download PPT slide]   Figure 14a.  Cerebral lymphoma. (a) Axial T2-weighted fast SE (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial T1-weighted nonenhanced SE (520/14, two signals averaged, 6-mm section thickness, 179 x 256 matrix), (c) axial T1-weighted contrast-enhanced SE (520/14, two signals averaged, 6-mm section thickness, 179 x 256), and (d) axial DW echo-planar (sensitizing direction = z) (800/123, one signal acquired, 6-mm section thickness) images and (e) corresponding ADC map. The enhancing component shows high signal intensity on the DW echo-planar image (d) and reduced ADC values (e). The peritumoral edema is hyperintense on the ADC map.

View larger version (136K): [in this window] [in a new window] [Download PPT slide]   Figure 14b.  Cerebral lymphoma. (a) Axial T2-weighted fast SE (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial T1-weighted nonenhanced SE (520/14, two signals averaged, 6-mm section thickness, 179 x 256 matrix), (c) axial T1-weighted contrast-enhanced SE (520/14, two signals averaged, 6-mm section thickness, 179 x 256), and (d) axial DW echo-planar (sensitizing direction = z) (800/123, one signal acquired, 6-mm section thickness) images and (e) corresponding ADC map. The enhancing component shows high signal intensity on the DW echo-planar image (d) and reduced ADC values (e). The peritumoral edema is hyperintense on the ADC map.

View larger version (131K): [in this window] [in a new window] [Download PPT slide]   Figure 14c.  Cerebral lymphoma. (a) Axial T2-weighted fast SE (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial T1-weighted nonenhanced SE (520/14, two signals averaged, 6-mm section thickness, 179 x 256 matrix), (c) axial T1-weighted contrast-enhanced SE (520/14, two signals averaged, 6-mm section thickness, 179 x 256), and (d) axial DW echo-planar (sensitizing direction = z) (800/123, one signal acquired, 6-mm section thickness) images and (e) corresponding ADC map. The enhancing component shows high signal intensity on the DW echo-planar image (d) and reduced ADC values (e). The peritumoral edema is hyperintense on the ADC map.

View larger version (129K): [in this window] [in a new window] [Download PPT slide]   Figure 14d.  Cerebral lymphoma. (a) Axial T2-weighted fast SE (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial T1-weighted nonenhanced SE (520/14, two signals averaged, 6-mm section thickness, 179 x 256 matrix), (c) axial T1-weighted contrast-enhanced SE (520/14, two signals averaged, 6-mm section thickness, 179 x 256), and (d) axial DW echo-planar (sensitizing direction = z) (800/123, one signal acquired, 6-mm section thickness) images and (e) corresponding ADC map. The enhancing component shows high signal intensity on the DW echo-planar image (d) and reduced ADC values (e). The peritumoral edema is hyperintense on the ADC map.

View larger version (82K): [in this window] [in a new window] [Download PPT slide]   Figure 14e.  Cerebral lymphoma. (a) Axial T2-weighted fast SE (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial T1-weighted nonenhanced SE (520/14, two signals averaged, 6-mm section thickness, 179 x 256 matrix), (c) axial T1-weighted contrast-enhanced SE (520/14, two signals averaged, 6-mm section thickness, 179 x 256), and (d) axial DW echo-planar (sensitizing direction = z) (800/123, one signal acquired, 6-mm section thickness) images and (e) corresponding ADC map. The enhancing component shows high signal intensity on the DW echo-planar image (d) and reduced ADC values (e). The peritumoral edema is hyperintense on the ADC map.

View larger version (159K): [in this window] [in a new window] [Download PPT slide]   Figure 15a.  Cerebral lymphoma with hyperintense and hypointense components on DW images. (a) T2-weighted fast SE, (b) contrast-enhanced T1-weighted SE, and (c) DW (trace) multishot echo-planar images and (d) corresponding ADC map. The central component of lymphoma in c shows peripheral hyperintensity and central hypointensity (due to necrosis?).

View larger version (104K): [in this window] [in a new window] [Download PPT slide]   Figure 15b.  Cerebral lymphoma with hyperintense and hypointense components on DW images. (a) T2-weighted fast SE, (b) contrast-enhanced T1-weighted SE, and (c) DW (trace) multishot echo-planar images and (d) corresponding ADC map. The central component of lymphoma in c shows peripheral hyperintensity and central hypointensity (due to necrosis?).

View larger version (88K): [in this window] [in a new window] [Download PPT slide]   Figure 15c.  Cerebral lymphoma with hyperintense and hypointense components on DW images. (a) T2-weighted fast SE, (b) contrast-enhanced T1-weighted SE, and (c) DW (trace) multishot echo-planar images and (d) corresponding ADC map. The central component of lymphoma in c shows peripheral hyperintensity and central hypointensity (due to necrosis?).

View larger version (128K): [in this window] [in a new window] [Download PPT slide]   Figure 15d.  Cerebral lymphoma with hyperintense and hypointense components on DW images. (a) T2-weighted fast SE, (b) contrast-enhanced T1-weighted SE, and (c) DW (trace) multishot echo-planar images and (d) corresponding ADC map. The central component of lymphoma in c shows peripheral hyperintensity and central hypointensity (due to necrosis?).

View larger version (166K): [in this window] [in a new window] [Download PPT slide]   Figure 16a.  Cerebral lymphoma with hyperintense and hypointense components on DW images (same case as Fig 15 but different level). (a) T2-weighted fast SE, (b) contrast-enhanced T1-weighted SE, and (c) DW (trace) multishot echo-planar images and (d) corresponding ADC map.

View larger version (132K): [in this window] [in a new window] [Download PPT slide]   Figure 16b.  Cerebral lymphoma with hyperintense and hypointense components on DW images (same case as Fig 15 but different level). (a) T2-weighted fast SE, (b) contrast-enhanced T1-weighted SE, and (c) DW (trace) multishot echo-planar images and (d) corresponding ADC map.

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 16c.  Cerebral lymphoma with hyperintense and hypointense components on DW images (same case as Fig 15 but different level). (a) T2-weighted fast SE, (b) contrast-enhanced T1-weighted SE, and (c) DW (trace) multishot echo-planar images and (d) corresponding ADC map.

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 16d.  Cerebral lymphoma with hyperintense and hypointense components on DW images (same case as Fig 15 but different level). (a) T2-weighted fast SE, (b) contrast-enhanced T1-weighted SE, and (c) DW (trace) multishot echo-planar images and (d) corresponding ADC map.

• A majority of lymphomas are either isointense or hypointense relative to gray matter on T2-weighted images (33% and 20%, respectively, in the study of Johnson et al [35]).
  
• Most lymphomas identified on long TR images enhance (homogeneous enhancement in immunocompetent patients; rim enhancement is more common in immunocompromised patients [36–39]).
  
• High signal intensity on DW images and low ADC values may favor the diagnosis of lymphoma versus glioma or metastasis (26).
  

Background and Discussion
In the reported cases of cerebral lymphomas, enhancing components were hyperintense on DW images and the contrast with white matter was as high as 9.4. An additional case of cerebral lymphoma showed a mixture of hyperintense and hypointense components, however (26). This may be related to necrosis. The reported ADC values were as low as 0.58 and 0.55 x 10^-3 mm²/sec ± 0.18 (26). Tumor cellularity is probably a major determinant of ADC values of cerebral lymphomas (26).

Conclusions
The initial reports suggest that the enhancing components of lymphomas are hyperintense on DW images and show low ADC values. A large study is needed to confirm the potential utility of DW imaging in the differential diagnosis of cerebral lymphomas, metastases, and glial tumors.

	Tumors: Epidermoid Cyst

Top Abstract Basic Physics of Diffusion... Acute Infarction Venous Infarction Tumors: Glioma Tumors: Metastases Tumors: Meningioma Tumors: Lymphoma Tumors: Epidermoid Cyst Inflammation: Abscess Inflammation: Granuloma Inflammation: Encephalitis Hemorrhage Multiple Sclerosis Creutzfeld-Jakob Disease Other Bright Lesions on... References

 
Typical Presentation on DW Images and ADC Maps
Epidermoid tumors are isointense to slightly hyperintense relative to cerebrospinal fluid on T1-, T2-, and proton density-weighted images (40-44); it is difficult to discern the exact extension of an epidermoid tumor with only T1-, T2-, or proton density-weighted imaging. On DW images, epidermoid tumors show high signal intensity and are easily differentiated from cerebrospinal fluid or arachnoid cysts (Figs 17, 18) (45). Constructive interference in the steady state (CISS) and FLAIR sequences also depict epidermoid tumors in the subarachnoid spaces better than conventional SE images (46). The reported mean ADC value of epidermoid tumors was 1.197 x 10^-3 mm²/sec (47–50. In our experience, the ADC values of epidermoid cyst and gray and white matter are similar. Therefore, the high signal intensity of epidermoid cysts on DW images suggests the T2 shine-through effect.

View larger version (188K): [in this window] [in a new window] [Download PPT slide]   Figure 17a.  Epidermoid cyst. (a) Axial T2-weighted, (b) T1-weighted SE, and (c) corresponding DW images (trace) and (d) ADC map show typical high signal intensity of epidermoid cyst on DW images (c) and isointensity with white and gray matter on ADC maps (d).

View larger version (165K): [in this window] [in a new window] [Download PPT slide]   Figure 17b.  Epidermoid cyst. (a) Axial T2-weighted, (b) T1-weighted SE, and (c) corresponding DW images (trace) and (d) ADC map show typical high signal intensity of epidermoid cyst on DW images (c) and isointensity with white and gray matter on ADC maps (d).

View larger version (150K): [in this window] [in a new window] [Download PPT slide]   Figure 17c.  Epidermoid cyst. (a) Axial T2-weighted, (b) T1-weighted SE, and (c) corresponding DW images (trace) and (d) ADC map show typical high signal intensity of epidermoid cyst on DW images (c) and isointensity with white and gray matter on ADC maps (d).

View larger version (123K): [in this window] [in a new window] [Download PPT slide]   Figure 17d.  Epidermoid cyst. (a) Axial T2-weighted, (b) T1-weighted SE, and (c) corresponding DW images (trace) and (d) ADC map show typical high signal intensity of epidermoid cyst on DW images (c) and isointensity with white and gray matter on ADC maps (d).

View larger version (153K): [in this window] [in a new window] [Download PPT slide]   Figure 18a.  Arachnoid cyst plus meningioma. (a) Axial T2-weighted, (b) contrast-enhanced T1-weighted SE, and (c) corresponding DW images (sensitizing direction = z) and (d) ADC (trace) map. The arachnoid cyst has typical low signal intensity on the DW image (c) and isointensity with CSF on the ADC map (d).

View larger version (123K): [in this window] [in a new window] [Download PPT slide]   Figure 18b.  Arachnoid cyst plus meningioma. (a) Axial T2-weighted, (b) contrast-enhanced T1-weighted SE, and (c) corresponding DW images (sensitizing direction = z) and (d) ADC (trace) map. The arachnoid cyst has typical low signal intensity on the DW image (c) and isointensity with CSF on the ADC map (d).

View larger version (177K): [in this window] [in a new window] [Download PPT slide]   Figure 18c.  Arachnoid cyst plus meningioma. (a) Axial T2-weighted, (b) contrast-enhanced T1-weighted SE, and (c) corresponding DW images (sensitizing direction = z) and (d) ADC (trace) map. The arachnoid cyst has typical low signal intensity on the DW image (c) and isointensity with CSF on the ADC map (d).

View larger version (118K): [in this window] [in a new window] [Download PPT slide]   Figure 18d.  Arachnoid cyst plus meningioma. (a) Axial T2-weighted, (b) contrast-enhanced T1-weighted SE, and (c) corresponding DW images (sensitizing direction = z) and (d) ADC (trace) map. The arachnoid cyst has typical low signal intensity on the DW image (c) and isointensity with CSF on the ADC map (d).

The differential diagnosis of epidermoid and arachnoid cyst is straightforward on DW images. The epidermoid cyst is bright, while the arachnoid cyst is dark. CISS and FLAIR sequences are also useful.

Hints for differential diagnosis:

• Signal intensity on DW imges, ADC maps, CISS images, and FLAIR images (Table 4)
  
• Epidermoid tumors insinuate along CSF spaces and encase arteries and cranial nerves, whereas arachnoid cyst displace adjacent structures (51).
  

Conclusions
It is difficult to discern the exact extension of an epidermoid tumor by using only T1-,T2-, or proton density-weighted imaging. The differential diagnosis of arachnoid cyst may also be impossible on T2-, T1-, and proton density-weighted SE images, whereas it is straightforward on DW images. On the latter, the epidermoid cyst is bright while the arachnoid cyst is dark. The ADC values of epidermoid cyst and of gray and white matter are similar. Therefore, the high signal intensity of epidermoid cysts on DW images is related to the T2 shine-through effect.

	Inflammation: Abscess

Top Abstract Basic Physics of Diffusion... Acute Infarction Venous Infarction Tumors: Glioma Tumors: Metastases Tumors: Meningioma Tumors: Lymphoma Tumors: Epidermoid Cyst Inflammation: Abscess Inflammation: Granuloma Inflammation: Encephalitis Hemorrhage Multiple Sclerosis Creutzfeld-Jakob Disease Other Bright Lesions on... References

 
Typical Presentation on DW Images and ADC Maps
The reported cases of cerebral abscess showed central hyperintensity on DW echo-planar images (Fig 19) and strongly reduced ADC values (range, 0.27–0.64 x 10^-3 mm²/sec) (52–56)

View larger version (169K): [in this window] [in a new window] [Download PPT slide]   Figure 19a.  Cerebral abscess (Streptococcus intermedius, Fusobacterium nucleatum and Actinomyces meyeri). (a) Axial T2-weighted fast SE (5300/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial T1-weighted contrast-enhanced SE (580/14, two signals averaged, 6-mm section thickness, 192 x 256 matrix), and (c) axial DW (sensitizing direction = x) multishot echo-planar (800/123, one signal acquired, 6-mm section thickness) images and (d) corresponding ADC map.

View larger version (102K): [in this window] [in a new window] [Download PPT slide]   Figure 19b.  Cerebral abscess (Streptococcus intermedius, Fusobacterium nucleatum and Actinomyces meyeri). (a) Axial T2-weighted fast SE (5300/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial T1-weighted contrast-enhanced SE (580/14, two signals averaged, 6-mm section thickness, 192 x 256 matrix), and (c) axial DW (sensitizing direction = x) multishot echo-planar (800/123, one signal acquired, 6-mm section thickness) images and (d) corresponding ADC map.

View larger version (153K): [in this window] [in a new window] [Download PPT slide]   Figure 19c.  Cerebral abscess (Streptococcus intermedius, Fusobacterium nucleatum and Actinomyces meyeri). (a) Axial T2-weighted fast SE (5300/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial T1-weighted contrast-enhanced SE (580/14, two signals averaged, 6-mm section thickness, 192 x 256 matrix), and (c) axial DW (sensitizing direction = x) multishot echo-planar (800/123, one signal acquired, 6-mm section thickness) images and (d) corresponding ADC map.

View larger version (102K): [in this window] [in a new window] [Download PPT slide]   Figure 19d.  Cerebral abscess (Streptococcus intermedius, Fusobacterium nucleatum and Actinomyces meyeri). (a) Axial T2-weighted fast SE (5300/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial T1-weighted contrast-enhanced SE (580/14, two signals averaged, 6-mm section thickness, 192 x 256 matrix), and (c) axial DW (sensitizing direction = x) multishot echo-planar (800/123, one signal acquired, 6-mm section thickness) images and (d) corresponding ADC map.

Hints for differential diagnosis:

• Clinical presentation (typically acute onset in ischemic stroke).
  
• Parenchymal contrast material uptake (unusual in subacute ischemic stroke).
  
• ADC values (reported ADC values of cerebral abscesses are ±50% lower than those of ischemic stroke after 8 hours).
  

Differential Diagnosis of Abscess and Cystic or Necrotic Tumors
The differential diagnosis of intracerebral necrotic tumors and cerebral abscesses is frequently impossible on conventional MR images. The DW image is a diagnostic clue in cases of a cerebral ring-enhancing mass. Pyogenic brain abscess has been reported to have markedly increased signal intensity on DW images and markedly decreased signal intensity on ADC maps, while the opposite happens in necrotic tumors (Fig 20). However, Tung et al recently reported two metastases, both squamous cell carcinomas, and one case of radiation necrosis with markedly increased signal intensity on DW images and a low ADC value (32). They speculate that restricted diffusion in these cases was due to sterile liquefaction necrosis.

View larger version (157K): [in this window] [in a new window] [Download PPT slide]   Figure 20a.  Glioblastoma multiforme. On (a) T2-weighted fast SE and (b) contrast-enhanced T1-weighted SE images, the differential diagnosis of glioblastoma and abscess is impossible. (c) DW (sensitizing direction = z) multishot echo-planar image (800/123, five signals averaged, 6-mm section thickness) and (d) corresponding ADC map show central hypointensity on DW image and hyperintensity on ADC map, consistent with the diagnosis of tumor.

View larger version (102K): [in this window] [in a new window] [Download PPT slide]   Figure 20b.  Glioblastoma multiforme. On (a) T2-weighted fast SE and (b) contrast-enhanced T1-weighted SE images, the differential diagnosis of glioblastoma and abscess is impossible. (c) DW (sensitizing direction = z) multishot echo-planar image (800/123, five signals averaged, 6-mm section thickness) and (d) corresponding ADC map show central hypointensity on DW image and hyperintensity on ADC map, consistent with the diagnosis of tumor.

View larger version (173K): [in this window] [in a new window] [Download PPT slide]   Figure 20c.  Glioblastoma multiforme. On (a) T2-weighted fast SE and (b) contrast-enhanced T1-weighted SE images, the differential diagnosis of glioblastoma and abscess is impossible. (c) DW (sensitizing direction = z) multishot echo-planar image (800/123, five signals averaged, 6-mm section thickness) and (d) corresponding ADC map show central hypointensity on DW image and hyperintensity on ADC map, consistent with the diagnosis of tumor.

View larger version (112K): [in this window] [in a new window] [Download PPT slide]   Figure 20d.  Glioblastoma multiforme. On (a) T2-weighted fast SE and (b) contrast-enhanced T1-weighted SE images, the differential diagnosis of glioblastoma and abscess is impossible. (c) DW (sensitizing direction = z) multishot echo-planar image (800/123, five signals averaged, 6-mm section thickness) and (d) corresponding ADC map show central hypointensity on DW image and hyperintensity on ADC map, consistent with the diagnosis of tumor.

• Presentation on DW images and ADC values. The cystic or necrotic components of tumors show marked signal suppression on DW images, similar to that of the CSF, and the reported ADC values are in the range of 2.2 x 10^-3 mm²/sec ± 0.9 (30) and 1.65–2.62 x 10^-3 mm²/sec (31).
  

Background and Discussion
Imaging

The MR features of brain abscesses vary with lesion stage. During the initial cerebritis stage, an ill-defined subcortical hyperintense zone on T2-weighted images is associated with poorly delineated enhancing areas within the iso- to mildly hypointense edematous region on contrast-enhanced T1-weighted images (57). During the early and late capsule stages, the collagenous abscess capsule is visible on unenhanced images as a comparatively thin-walled, well-delineated iso- to slightly hyperintense ring that becomes hypointense with T2-weighted sequences (57). Nonetheless, a ring-enhancing mass is a nonspecific imaging finding that can be seen in various noninflammatory benign and neoplastic processes. The differential diagnosis includes primary brain tumors (eg, necrotic glioblastoma), metastases, resolving hematoma, infarction, and even demyelinating disease (57). Lövblad et al (11) reported only two false-positive findings in 194 cases of acute ischemic stroke. One false-positive finding was a cerebral abscess, and the other was a brain tumor. ADC values, however, were not calculated in this study (11), and the T2 shine-through effect remains a possible explanation for these findings. The reported ADC values for acute ischemic stroke vary with time. Lutsep et al (7) reported ADC values of 0.29–0.33 x 10^-3 mm²/sec for ischemic lesions studied less than 8 hours after symptom onset, 0.61 x 10^-3 mm²/sec ± 0.14 at 8–24 hours, and 0.51 x 10^-3 mm²/sec ± 0.18 at 1–8 days. Mean normal ADC values for the entire group (n = 26) were 0.88 x 10^-3 mm²/sec ± 0.12. The reported mean ADC values in the central part of the abscess are ±50%lower than ADC values of ischemic stroke after 8 hours (0.29 and 0.27 x 10^-3 mm²/sec in the study of Desprechins et al [52], 0.31 x 10^-3 mm²/sec in the report of Ebisu et al [53]). Increased signal intensity on DW images was also reported in a case of subdural empyema (54). On the other hand, the cystic or necrotic components of tumors show a marked signal suppression on DW images, similar to that of CSF, and the calculated ADC values are in the range of 2.2 x 10^-3 mm²/sec ± 0.9 (30,52,55). However, recently Tung et al reported two metastases, both squamous cell carcinomas, and one case of radiation necrosis with markedly increased signal intensity on DW images and a low ADC value (32). However, this presentation was unusual. Only five of 30 rim-enhancing masses had high signal intensity on DW images and low ADC values; two of these five cases were brain abscesses, two were metastases from lung squamous cell carcinoma, and one was radiation necrosis.

Presumed Causes of High Signal Intensity on DW Images

These findings support the idea that reduced ADC values in the central part of the abscess are related to the presence of pus. Ebisu et al (53) performed in vitro DW imaging of aspirated pus, as well as ADC measurements. The pus imaged in vitro showed high signal intensity and low ADC values, similar to the results of the in vivo study. He concluded that the pus structure itself is responsible for the low ADC values, and that the heavily impeded water mobility of pus may be related to its high cellularity and viscosity. The presence of large molecules, such as fibrinogen, also may play a key role in restricting the diffusion of protons in pus (58).

Conclusions
Brain abscesses are potentially fatal lesions, and a correct diagnosis should be established as soon as possible. Establishing the differential diagnosis of intracerebral necrotic tumors and cerebral abscesses is frequently impossible with conventional MR imaging. DW imaging and ADC maps are useful in the differential diagnosis of ring-enhancing cerebral masses. The presence of central hyperintensity on DW images and low ADC values strongly suggest the presence of pus and abscess. The differential diagnosis includes acute infarction, which also shows hyperintensity on DW images and reduced ADC values. Nevertheless, the ring enhancement in acute ischemic stroke is unusual, and ADC values are higher after 8 hours. The ring-enhancing mass with central hypointensity on DW images and an increase in ADC values suggest necrotic tumor, most frequently cerebral glioma or metastasis. For these reasons, DW imaging and calculations of ADC values should be performed in all cases of ring-enhancing cerebral masses.

	Inflammation: Granuloma

Top Abstract Basic Physics of Diffusion... Acute Infarction Venous Infarction Tumors: Glioma Tumors: Metastases Tumors: Meningioma Tumors: Lymphoma Tumors: Epidermoid Cyst Inflammation: Abscess Inflammation: Granuloma Inflammation: Encephalitis Hemorrhage Multiple Sclerosis Creutzfeld-Jakob Disease Other Bright Lesions on... References

 
Typical Presentation on DW Images and ADC Maps
The reported case of granuloma was hyperintense on DW images, and the calculated ADC values were decreased (0.39 x 10^-3 mm²/sec) (26). In our experience, the increased signal intensity on DW images and a low ADC value are usual in inflammatory granulomas (Fig 21).

View larger version (165K): [in this window] [in a new window] [Download PPT slide]   Figure 21a.  Multiple Tbc granulomas. (a) Axial T2-weighted fast SE, (b) FLAIR, (c) contrast-enhanced T1-weighted SE, and (d) DW (sensitizing direction = z) images and (e) corresponding ADC map. Some of the granulomas show high signal intensity on DW images (c), but ADC values are similar to those of white matter.

View larger version (186K): [in this window] [in a new window] [Download PPT slide]   Figure 21b.  Multiple Tbc granulomas. (a) Axial T2-weighted fast SE, (b) FLAIR, (c) contrast-enhanced T1-weighted SE, and (d) DW (sensitizing direction = z) images and (e) corresponding ADC map. Some of the granulomas show high signal intensity on DW images (c), but ADC values are similar to those of white matter.

View larger version (130K): [in this window] [in a new window] [Download PPT slide]   Figure 21c.  Multiple Tbc granulomas. (a) Axial T2-weighted fast SE, (b) FLAIR, (c) contrast-enhanced T1-weighted SE, and (d) DW (sensitizing direction = z) images and (e) corresponding ADC map. Some of the granulomas show high signal intensity on DW images (c), but ADC values are similar to those of white matter.

View larger version (129K): [in this window] [in a new window] [Download PPT slide]   Figure 21d.  Multiple Tbc granulomas. (a) Axial T2-weighted fast SE, (b) FLAIR, (c) contrast-enhanced T1-weighted SE, and (d) DW (sensitizing direction = z) images and (e) corresponding ADC map. Some of the granulomas show high signal intensity on DW images (c), but ADC values are similar to those of white matter.

View larger version (137K): [in this window] [in a new window] [Download PPT slide]   Figure 21e.  Multiple Tbc granulomas. (a) Axial T2-weighted fast SE, (b) FLAIR, (c) contrast-enhanced T1-weighted SE, and (d) DW (sensitizing direction = z) images and (e) corresponding ADC map. Some of the granulomas show high signal intensity on DW images (c), but ADC values are similar to those of white matter.

View larger version (158K): [in this window] [in a new window] [Download PPT slide]   Figure 22a.  Cerebral metastases. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (sensitizing direction = z) images and (e) corresponding ADC map. These multiple metastases of a small-cell lung carcinoma had high cellularity at histologic study.

View larger version (152K): [in this window] [in a new window] [Download PPT slide]   Figure 22b.  Cerebral metastases. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (sensitizing direction = z) images and (e) corresponding ADC map. These multiple metastases of a small-cell lung carcinoma had high cellularity at histologic study.

View larger version (122K): [in this window] [in a new window] [Download PPT slide]   Figure 22c.  Cerebral metastases. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (sensitizing direction = z) images and (e) corresponding ADC map. These multiple metastases of a small-cell lung carcinoma had high cellularity at histologic study.

View larger version (131K): [in this window] [in a new window] [Download PPT slide]   Figure 22d.  Cerebral metastases. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (sensitizing direction = z) images and (e) corresponding ADC map. These multiple metastases of a small-cell lung carcinoma had high cellularity at histologic study.

View larger version (85K): [in this window] [in a new window] [Download PPT slide]   Figure 22e.  Cerebral metastases. (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (sensitizing direction = z) images and (e) corresponding ADC map. These multiple metastases of a small-cell lung carcinoma had high cellularity at histologic study.

View larger version (165K): [in this window] [in a new window] [Download PPT slide]   Figure 23a.  Cerebral metastases (same case as Fig 22 but different level). (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (sensitizing direction = z) images and (e) corresponding ADC map.

View larger version (160K): [in this window] [in a new window] [Download PPT slide]   Figure 23b.  Cerebral metastases (same case as Fig 22 but different level). (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (sensitizing direction = z) images and (e) corresponding ADC map.

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 23c.  Cerebral metastases (same case as Fig 22 but different level). (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (sensitizing direction = z) images and (e) corresponding ADC map.

View larger version (144K): [in this window] [in a new window] [Download PPT slide]   Figure 23d.  Cerebral metastases (same case as Fig 22 but different level). (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (sensitizing direction = z) images and (e) corresponding ADC map.

View larger version (128K): [in this window] [in a new window] [Download PPT slide]   Figure 23e.  Cerebral metastases (same case as Fig 22 but different level). (a) Axial T2-weighted fast SE, (b, c) T1-weighted (b) nonenhanced and (c) contrast-enhanced SE, and (d) DW (sensitizing direction = z) images and (e) corresponding ADC map.

	Inflammation: Encephalitis

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Typical Presentation on DW Images and ADC Maps
Herpes encephalitis lesions are characterized by marked hyperintensity on DW images and reduced ADC values (48%–66%of that of normal brain parenchyma) (59). On follow-up T1- and T2-weighted MR images, these areas demonstrate encephalomalacic change (Fig 24) (59). All eight patients with Nipah virus infection reported by Lim et al (60) had multiple small bilateral foci within the subcortical and deep white matter on T2-weighted images. In five patients, DW images showed increased signal intensity.

View larger version (75K): [in this window] [in a new window] [Download PPT slide]   Figure 24a.  Herpes encephalitis. (a) Axial T2-weighted fast SE (5400/90, one signal acquired, 6-mm section thickness, one echo, 192 x 256 matrix), (b) axial T1-weighted nonenhanced SE (580/14, two signals averaged, 6-mm section thickness), and (c) axial T1-weighted contrast-enhanced (580/14, two signals averaged, 6-mm section thickness) images. On the T2-weighted SE image, heterogeneous hyperintense lesions (arrows) are seen in the temporal and hippocampal areas. On the nonenhanced T1-weighted SE image, less extensive hyperintense areas (hemorrhages) can also be recognized (arrow). After gadolinium injection, asymmetric, gyriform enhancement is seen in the temporal lobes (arrow) and cingulate gyrus, characteristic of herpes encephalitis.

View larger version (76K): [in this window] [in a new window] [Download PPT slide]   Figure 24b.  Herpes encephalitis. (a) Axial T2-weighted fast SE (5400/90, one signal acquired, 6-mm section thickness, one echo, 192 x 256 matrix), (b) axial T1-weighted nonenhanced SE (580/14, two signals averaged, 6-mm section thickness), and (c) axial T1-weighted contrast-enhanced (580/14, two signals averaged, 6-mm section thickness) images. On the T2-weighted SE image, heterogeneous hyperintense lesions (arrows) are seen in the temporal and hippocampal areas. On the nonenhanced T1-weighted SE image, less extensive hyperintense areas (hemorrhages) can also be recognized (arrow). After gadolinium injection, asymmetric, gyriform enhancement is seen in the temporal lobes (arrow) and cingulate gyrus, characteristic of herpes encephalitis.

View larger version (72K): [in this window] [in a new window] [Download PPT slide]   Figure 24c.  Herpes encephalitis. (a) Axial T2-weighted fast SE (5400/90, one signal acquired, 6-mm section thickness, one echo, 192 x 256 matrix), (b) axial T1-weighted nonenhanced SE (580/14, two signals averaged, 6-mm section thickness), and (c) axial T1-weighted contrast-enhanced (580/14, two signals averaged, 6-mm section thickness) images. On the T2-weighted SE image, heterogeneous hyperintense lesions (arrows) are seen in the temporal and hippocampal areas. On the nonenhanced T1-weighted SE image, less extensive hyperintense areas (hemorrhages) can also be recognized (arrow). After gadolinium injection, asymmetric, gyriform enhancement is seen in the temporal lobes (arrow) and cingulate gyrus, characteristic of herpes encephalitis.

• If confirmed, the hyperintensity on DW images and reduced ADC values favor the diagnosis of herpes encephalitis.
  
• Biological tests (polymerase chain reaction test).
  

The differential diagnosis between acute ischemic stroke and herpes encephalitis may be problematic on DW images.

Hints for differential diagnosis herpes encephalitis versus ischemic stroke:

• Clinical presentation (acute onset in ischemic stroke, more progressive in herpes encephalitis).
  
• Biological tests (polymerase chain reaction test).
  

Background and Discussion
Herpes encephalitis lesions are characterized by marked hyperintensity on DW images and reduced ADC values (48%–66%of the normal brain parenchyma) (59). On follow-up T1- and T2-weighted MR images, these areas demonstrate encephalomalacic change (59). DW images may aid in distinguishing herpes lesions from infiltrative temporal lobe tumors because the ADCs of herpes lesions are low while the ADCs of various tumors are elevated or in the normal range (26,30,59). All eight patients with Nipah virus infection reported by Lim et al (60) had multiple small bilateral foci within the subcortical and deep white matter on T2-weighted images. In five patients, DW images showed increased signal intensity. The restricted diffusion is explained by cytotoxic edema in tissue undergoing necrosis (59).

Conclusions
Initial reports suggest that herpes encephalitis lesions are characterized by marked hyperintensity on DW images and reduced ADC values (48%–66%of those of normal brain parenchyma) (59).

	Hemorrhage

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Typical Presentation on DW Images and ADC Maps
High signal intensity on DW images is reported in hyperacute (intracellular oxyhemoglobin) and late subacute (extracellular methemoglobin) stages of hemorrhage (Figs 25, 26; Table 5) (61,62). The ADC values are reported to be decreased (61) or normal (62) in hyperacute stages and increased in the late subacute stage (61).

View larger version (198K): [in this window] [in a new window] [Download PPT slide]   Figure 25a.  Hyperacute hemorrhage (4 hours after onset). (a) T2- and (b) T1-weighted SE and (c) DW (sensitizing direction = z) multishot echo-planar images and (d) corresponding ADC map.

View larger version (160K): [in this window] [in a new window] [Download PPT slide]   Figure 25b.  Hyperacute hemorrhage (4 hours after onset). (a) T2- and (b) T1-weighted SE and (c) DW (sensitizing direction = z) multishot echo-planar images and (d) corresponding ADC map.

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 25c.  Hyperacute hemorrhage (4 hours after onset). (a) T2- and (b) T1-weighted SE and (c) DW (sensitizing direction = z) multishot echo-planar images and (d) corresponding ADC map.

View larger version (68K): [in this window] [in a new window] [Download PPT slide]   Figure 25d.  Hyperacute hemorrhage (4 hours after onset). (a) T2- and (b) T1-weighted SE and (c) DW (sensitizing direction = z) multishot echo-planar images and (d) corresponding ADC map.

View larger version (162K): [in this window] [in a new window] [Download PPT slide]   Figure 26a.  Late subacute stage hemmorhage (27 days after onset). (a) T2- and (b) T1-weighted SE and (c) DW (trace) multishot echo-planar images and (d) corresponding ADC map.

View larger version (128K): [in this window] [in a new window] [Download PPT slide]   Figure 26b.  Late subacute stage hemmorhage (27 days after onset). (a) T2- and (b) T1-weighted SE and (c) DW (trace) multishot echo-planar images and (d) corresponding ADC map.

View larger version (114K): [in this window] [in a new window] [Download PPT slide]   Figure 26c.  Late subacute stage hemmorhage (27 days after onset). (a) T2- and (b) T1-weighted SE and (c) DW (trace) multishot echo-planar images and (d) corresponding ADC map.

View larger version (123K): [in this window] [in a new window] [Download PPT slide]   Figure 26d.  Late subacute stage hemmorhage (27 days after onset). (a) T2- and (b) T1-weighted SE and (c) DW (trace) multishot echo-planar images and (d) corresponding ADC map.

Hints for differential diagnosis:

• In hyperacute ischemic stroke the T2-weighted SE and T2*-weighted gradient-echo findings are normal.
  
• In hyperacute hemorrhage, heterogeneous hyperintensity with a hypointense rim is seen on T2-weighted SE and T2*-weighted gradient-echo images.
  

Background and Discussion
The MR appearance of evolving intracranial hemorrhage and its underlying biophysical basis are somewhat complex on conventional MR images and even more on DW images. High signal intensity on DW images is reported in hyperacute (intracellular oxyhemoglobin) and late subacute (extracellular methemoglobin) stages of hemorrhage (61,62). The ADC values are reported to be decreased (61) or normal (62) in hyperacute stages and increased in the late subacute stage (61).

Hyperacute Stage (intracellular oxyhemoglobin)

Atlas et al reported two cases of hyperacute hematomas (61). The signal intensity on DW images was not reported. The ADC values were 0.1 and 0.54 x 10^-3 mm²/sec. In this study the ADC measurements of all hematomas with intact red cell membranes (including hyperacute, acute, and even early subacute) were significantly reduced compared with normal brain tissue (61).

Postulated biophysical explanations for the observed restriction of diffusion in early stages of intracranial hemorrhage have included:

1. A shrinkage of the extracellular space with clot retraction (63).
   
2. A change in the osmotic environment once blood becomes extravascular, which alters the shape of red blood cells (64).
   
3. A phenomenon related to the formation of the fibrin network associated with clot (65).
   
4. A conformational change of the hemoglobin macromolecule within the red blood cell (66).
   

Maldjian et al reported four cases of hyperacute hematoma with high signal intensity on DW images (62). The ADC values were in the range 0.47–0.81 (mean, 0.63) x 10^-3 mm²/sec. There was no significant difference in the mean trace ADC values (calculated by using the method of expected values) between hematomas that were bright on T2-weighted images (mean, 0.631 x 10^-3 mm²/sec, SD = 0.14), hematomas that were dark on T2-weighted images (mean, 0.739 x 10^-3 mm²/sec, SD = 0.22), and contralateral white matter regions (mean, 0.830, SD = 0.20, P = .36). These results are in complete disagreement with the previous study (61). The possible explanation is the "T2 blackout effect," which is the corollary of the T2 shine-through effect. Hematomas that are dark on T2-weighted images have very low signal intensity, often at the level of the background noise, and obtaining accurate diffusion trace measurements may be flawed by background masking (a commonly used data processing strategy to reduce computational load by limiting the voxels in an analysis). Thus, artificially low estimates for diffusion trace values can be obtained in any areas that have signal intensities in the range of the background (hematomas, hemorrhagic strokes) and in which background masking was used (62). In our experience (four cases), the hyperacute hemorrhage was hyperintense on DW images, with heterogeneous hypointense components and reduced-to-normal ADC values (Table 6).

Late Subacute Stage (extracellular methemoglobin)

Atlas et al reported three cases of late subacute hematoma (61). The signal intensity on DW images was not reported. The ADC values were in the range 0.99–1.05 (mean, 1.02) x 10^-3 mm²/sec). They hypothesized that hematomas in which red blood cell membranes have lysed show considerably more diffusion (higher ADC values). In our experience (six cases), late subacute hematomas were strongly hyperintense on DW images, with ADC values in the range of 0.12–0.63 (mean, 0.48 SD = 0.33) x 10^-3 mm²/sec. Because the ADC values of intracellular oxyhemoglobin and extracellular methemoglobin are not decreased, the hyperintensity on DW images must be related to T2 and T1 shine-through effects.

Conclusions
The recognition of early intracranial hemorrhage, specifically on MR images, has become important because the primary assessment of patients with early stroke is moving toward MR imaging and away from CT scanning. As DW imaging becomes integrated into the initial emergent evaluation of patients with acute stroke (10,12,67), it becomes paramount to understand the manifestations of intracranial hemorrhage on DW MR imaging specifically. The differential diagnosis of hyperacute ischemic stroke and hemorrhage may be impossible on DW images and ADC maps alone. Therefore, the conjoint use of DW imaging and ADC maps with T2-weighted SE, T2*-weighted gradient-echo, and/or T2-weighted echo-planar imaging, especially during the therapeutic window for thrombolysis (up to 3 hours after onset), is mandatory in differentiation of hyperacute stroke from hyperacute hemorrhage. High signal intensity on DW images has been reported in hyperacute (intracellular oxyhemoglobin) and late subacute (extracellular methemoglobin) stages of hemorrhage (61,62). The ADC values are reported to be decreased (61) or normal (62) in hyperacute stages and increased in the late subacute stage (61).

	Multiple Sclerosis

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Typical Presentation on DW Images and ADC Maps
In our experience, the signal intensity of multiple sclerosis (MS) on DW images is variable (hyper-, iso-, or hypointense) (Fig 27). Gass et al (68) reported that enhancing lesions were hyperintense relative to white matter on DW images, while chronic lesions were isointense. Most studies focus on ADC values in MS. These studies show an increase in ADC values in MS lesions and perhaps also in the ADC values of normal-appearing white matter of MS patients (69-74). Therefore, we can hypothesize that the increased intensity in MS lesions on DW images results from the T2 shine-through effect.

View larger version (157K): [in this window] [in a new window] [Download PPT slide]   Figure 27a.  Multiple sclerosis, with recent hypoesthesia in the left lower limb. (a) Axial T2-weighted fast SE (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial fast FLAIR (6000/105, 2200-msec inversion time, two signals averaged, 6-mm section thickness, 182 x 256 matrix), (c) axial T1-weighted contrast-enhanced SE (540/14, two signals averaged, 6-mm section thickness, 230 x 512 matrix) images. (d) Axial DW (sensitizing direction = x) multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness) and (e) corresponding ADC map. (f) Axial DW (sensitizing direction = z) multishot echo-planar image and (g) corresponding ADC map. Active plaque is seen with contrast enhancement (c). Two additional small plaques are recognized on the FLAIR iamge (b). The ADC values of active plaque are increased; however, depending on the orientation of the corticospinal fibers, the conspicuity may be lower with respect to conventional sequences. This homogeneously enhancing lesion shows high signal intensity on DW images (d, f) and increased ADC values (e, g). The small, nonenhancing plaques are not recognized on the DW images and ADC maps.

View larger version (98K): [in this window] [in a new window] [Download PPT slide]   Figure 27b.  Multiple sclerosis, with recent hypoesthesia in the left lower limb. (a) Axial T2-weighted fast SE (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial fast FLAIR (6000/105, 2200-msec inversion time, two signals averaged, 6-mm section thickness, 182 x 256 matrix), (c) axial T1-weighted contrast-enhanced SE (540/14, two signals averaged, 6-mm section thickness, 230 x 512 matrix) images. (d) Axial DW (sensitizing direction = x) multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness) and (e) corresponding ADC map. (f) Axial DW (sensitizing direction = z) multishot echo-planar image and (g) corresponding ADC map. Active plaque is seen with contrast enhancement (c). Two additional small plaques are recognized on the FLAIR iamge (b). The ADC values of active plaque are increased; however, depending on the orientation of the corticospinal fibers, the conspicuity may be lower with respect to conventional sequences. This homogeneously enhancing lesion shows high signal intensity on DW images (d, f) and increased ADC values (e, g). The small, nonenhancing plaques are not recognized on the DW images and ADC maps.

View larger version (99K): [in this window] [in a new window] [Download PPT slide]   Figure 27c.  Multiple sclerosis, with recent hypoesthesia in the left lower limb. (a) Axial T2-weighted fast SE (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial fast FLAIR (6000/105, 2200-msec inversion time, two signals averaged, 6-mm section thickness, 182 x 256 matrix), (c) axial T1-weighted contrast-enhanced SE (540/14, two signals averaged, 6-mm section thickness, 230 x 512 matrix) images. (d) Axial DW (sensitizing direction = x) multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness) and (e) corresponding ADC map. (f) Axial DW (sensitizing direction = z) multishot echo-planar image and (g) corresponding ADC map. Active plaque is seen with contrast enhancement (c). Two additional small plaques are recognized on the FLAIR iamge (b). The ADC values of active plaque are increased; however, depending on the orientation of the corticospinal fibers, the conspicuity may be lower with respect to conventional sequences. This homogeneously enhancing lesion shows high signal intensity on DW images (d, f) and increased ADC values (e, g). The small, nonenhancing plaques are not recognized on the DW images and ADC maps.

View larger version (95K): [in this window] [in a new window] [Download PPT slide]   Figure 27d.  Multiple sclerosis, with recent hypoesthesia in the left lower limb. (a) Axial T2-weighted fast SE (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial fast FLAIR (6000/105, 2200-msec inversion time, two signals averaged, 6-mm section thickness, 182 x 256 matrix), (c) axial T1-weighted contrast-enhanced SE (540/14, two signals averaged, 6-mm section thickness, 230 x 512 matrix) images. (d) Axial DW (sensitizing direction = x) multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness) and (e) corresponding ADC map. (f) Axial DW (sensitizing direction = z) multishot echo-planar image and (g) corresponding ADC map. Active plaque is seen with contrast enhancement (c). Two additional small plaques are recognized on the FLAIR iamge (b). The ADC values of active plaque are increased; however, depending on the orientation of the corticospinal fibers, the conspicuity may be lower with respect to conventional sequences. This homogeneously enhancing lesion shows high signal intensity on DW images (d, f) and increased ADC values (e, g). The small, nonenhancing plaques are not recognized on the DW images and ADC maps.

View larger version (95K): [in this window] [in a new window] [Download PPT slide]   Figure 27e.  Multiple sclerosis, with recent hypoesthesia in the left lower limb. (a) Axial T2-weighted fast SE (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial fast FLAIR (6000/105, 2200-msec inversion time, two signals averaged, 6-mm section thickness, 182 x 256 matrix), (c) axial T1-weighted contrast-enhanced SE (540/14, two signals averaged, 6-mm section thickness, 230 x 512 matrix) images. (d) Axial DW (sensitizing direction = x) multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness) and (e) corresponding ADC map. (f) Axial DW (sensitizing direction = z) multishot echo-planar image and (g) corresponding ADC map. Active plaque is seen with contrast enhancement (c). Two additional small plaques are recognized on the FLAIR iamge (b). The ADC values of active plaque are increased; however, depending on the orientation of the corticospinal fibers, the conspicuity may be lower with respect to conventional sequences. This homogeneously enhancing lesion shows high signal intensity on DW images (d, f) and increased ADC values (e, g). The small, nonenhancing plaques are not recognized on the DW images and ADC maps.

View larger version (99K): [in this window] [in a new window] [Download PPT slide]   Figure 27f.  Multiple sclerosis, with recent hypoesthesia in the left lower limb. (a) Axial T2-weighted fast SE (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial fast FLAIR (6000/105, 2200-msec inversion time, two signals averaged, 6-mm section thickness, 182 x 256 matrix), (c) axial T1-weighted contrast-enhanced SE (540/14, two signals averaged, 6-mm section thickness, 230 x 512 matrix) images. (d) Axial DW (sensitizing direction = x) multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness) and (e) corresponding ADC map. (f) Axial DW (sensitizing direction = z) multishot echo-planar image and (g) corresponding ADC map. Active plaque is seen with contrast enhancement (c). Two additional small plaques are recognized on the FLAIR iamge (b). The ADC values of active plaque are increased; however, depending on the orientation of the corticospinal fibers, the conspicuity may be lower with respect to conventional sequences. This homogeneously enhancing lesion shows high signal intensity on DW images (d, f) and increased ADC values (e, g). The small, nonenhancing plaques are not recognized on the DW images and ADC maps.

View larger version (97K): [in this window] [in a new window] [Download PPT slide]   Figure 27g.  Multiple sclerosis, with recent hypoesthesia in the left lower limb. (a) Axial T2-weighted fast SE (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial fast FLAIR (6000/105, 2200-msec inversion time, two signals averaged, 6-mm section thickness, 182 x 256 matrix), (c) axial T1-weighted contrast-enhanced SE (540/14, two signals averaged, 6-mm section thickness, 230 x 512 matrix) images. (d) Axial DW (sensitizing direction = x) multishot echo-planar image (800/123, one signal acquired, 6-mm section thickness) and (e) corresponding ADC map. (f) Axial DW (sensitizing direction = z) multishot echo-planar image and (g) corresponding ADC map. Active plaque is seen with contrast enhancement (c). Two additional small plaques are recognized on the FLAIR iamge (b). The ADC values of active plaque are increased; however, depending on the orientation of the corticospinal fibers, the conspicuity may be lower with respect to conventional sequences. This homogeneously enhancing lesion shows high signal intensity on DW images (d, f) and increased ADC values (e, g). The small, nonenhancing plaques are not recognized on the DW images and ADC maps.

Roychowdhury et al (74) postulated that the decrease in ADC of homogeneously enhancing lesions may be similar to the process in acute ischemia and postanoxic demyelination (shifts in intracellular water protons and changes in membrane permeability may lead to decreased ADC values). The influx of inflammatory cells and associated macromolecules may also lead to restriction of water diffusion and reduction in trace ADC. The increase in ADC is believed to be related to the disruption of myelin, leading to an increased extracellular space (68–72).

Conclusions
In our experience, the signal intensity of MS lesions on DW images is variable (hyper-, iso-, or hypointense). The majority of studies have showed increases in ADC values in MS lesions and perhaps in the ADC values of normal-appearing white matter of MS patients (69–74). Therefore, we can hypothesize that the increased intensity of MS lesions on DW images is due to the T2 shine-through effect. Occasionally, the high-intensity plaques on DW images (especially homogeneously enhancing lesions) may show reduced ADC values. Perhaps the subset of homogeneously enhancing lesions with a low trace ADC represents a very early enhancing lesion with marked inflammation and no substantial demyelination (74).

	Creutzfeld-Jakob Disease

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Typical Presentation on DW Images and ADC Maps
The reported cases of sporadic Creutzfeld-Jakob disease (CJD) showed high signal intensities in the basal ganglia (putamen and caudate nucleus) and in the cortex on DW images. The high signal intensities in the basal ganglia are also prevalent on T2-weighted and FLAIR images. The cortical hyperintensities are usually not visualized on T2-weighted and FLAIR images (advantage of DW imaging) (Fig 28).

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   Figure 28a.  CJD. (a) Axial T2-weighted SE, (b) FLAIR and (c) DW echo-planar images. The hyperintensity of the caudate nuclei is obvious on the FLAIR and DW images. The left occipital cortical involvement is best appreciated on the DW image. (d) Histology specimen shows astrogliosis and microvesicular spongiform degeneration. (All images courtesy of Philippe Demaerel, MD, University Hospitals, Leuven, Belgium.)

View larger version (165K): [in this window] [in a new window] [Download PPT slide]   Figure 28b.  CJD. (a) Axial T2-weighted SE, (b) FLAIR and (c) DW echo-planar images. The hyperintensity of the caudate nuclei is obvious on the FLAIR and DW images. The left occipital cortical involvement is best appreciated on the DW image. (d) Histology specimen shows astrogliosis and microvesicular spongiform degeneration. (All images courtesy of Philippe Demaerel, MD, University Hospitals, Leuven, Belgium.)

View larger version (118K): [in this window] [in a new window] [Download PPT slide]   Figure 28c.  CJD. (a) Axial T2-weighted SE, (b) FLAIR and (c) DW echo-planar images. The hyperintensity of the caudate nuclei is obvious on the FLAIR and DW images. The left occipital cortical involvement is best appreciated on the DW image. (d) Histology specimen shows astrogliosis and microvesicular spongiform degeneration. (All images courtesy of Philippe Demaerel, MD, University Hospitals, Leuven, Belgium.)

View larger version (155K): [in this window] [in a new window] [Download PPT slide]   Figure 28d.  CJD. (a) Axial T2-weighted SE, (b) FLAIR and (c) DW echo-planar images. The hyperintensity of the caudate nuclei is obvious on the FLAIR and DW images. The left occipital cortical involvement is best appreciated on the DW image. (d) Histology specimen shows astrogliosis and microvesicular spongiform degeneration. (All images courtesy of Philippe Demaerel, MD, University Hospitals, Leuven, Belgium.)

View larger version (158K): [in this window] [in a new window] [Download PPT slide]   Figure 29a.  Acute stroke 4 hours after onset. (a) Axial T2-weighted fast SE (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial fast FLAIR (6000/105, 2200-msec inversion time, two signals averaged, 6-mm section thickness, 182 x 256 matrix), and (c) axial DW (sensitizing direction = z) multishot echo-planar (800/123, one signal acquired, 6-mm section thickness) images. The cortical involvement of acute stroke (arrow, c) looks similar to the cortical hyperintensities of CJD.

View larger version (106K): [in this window] [in a new window] [Download PPT slide]   Figure 29b.  Acute stroke 4 hours after onset. (a) Axial T2-weighted fast SE (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial fast FLAIR (6000/105, 2200-msec inversion time, two signals averaged, 6-mm section thickness, 182 x 256 matrix), and (c) axial DW (sensitizing direction = z) multishot echo-planar (800/123, one signal acquired, 6-mm section thickness) images. The cortical involvement of acute stroke (arrow, c) looks similar to the cortical hyperintensities of CJD.

View larger version (132K): [in this window] [in a new window] [Download PPT slide]   Figure 29c.  Acute stroke 4 hours after onset. (a) Axial T2-weighted fast SE (5000/128; two signals averaged; 6-mm section thickness; echo train length, 23; matrix, 230 x 512), (b) axial fast FLAIR (6000/105, 2200-msec inversion time, two signals averaged, 6-mm section thickness, 182 x 256 matrix), and (c) axial DW (sensitizing direction = z) multishot echo-planar (800/123, one signal acquired, 6-mm section thickness) images. The cortical involvement of acute stroke (arrow, c) looks similar to the cortical hyperintensities of CJD.

• Clinical presentation (typically acute onset in ischemic stroke).
  
• ADC values (decreased in acute stroke, approximately similar to those of white matter in CJD).
  

Differential Diagnosis of CJD, Progressive Multifocal Leukoencephalopathy, and Subacute Sclerosing Panencephalitis (SSPE)
Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease of immunocompromised patients caused by human papovaviruses. Subacute sclerosing panencephalitis (SSPE) occurs several years after measles infection. SSPE typically starts with mental and behavioral abnormalities, myoclonia, tremor, and seizures. Multifocal, hyperintense foci in white matter and the basal ganglia have been reported in PML and SSPE on T2-weighted images (75).

Hints for differential diagnosis:

• On T2-weighetd and FLAIR images, PML and SSPE are associated with white matter lesions, while CJD is not.
  
• The high-signal-intensity cortical lesions on DW images may be also a hallmark of CJD.
  

Background and Discussion
CJD is a rare, transmissible disease (caused by an agent called a "prion," to distinguish it from a virus) that is characterized by rapidly progressive dementia, ataxia, and myoclonus. The diagnostic triad—progressive dementia, myoclonic jerks, and periodic sharp-wave EEG activity—may be lacking in as many as 25%of patients. The pathologic features of CJD are microvesicular spongiform degeneration, astrocytic glioses, and neuronal loss.

MR imaging of sporadic CJD may show high signal intensities in the basal ganglia (putamen, caudate nucleus) and cortex. Finkenstaedt et al (76), using T2- and proton density-weighted images reported bilateral, symmetrically increased signal intensity in the putamen and caudate nucleus in 79%of CJD patients, compared with just 7%of non-CJD dementia patients. More recently, the same authors reported high signal intensities in the basal ganglia and cortex on DW images in five CJD patients (77). Increased signal intensity in the globus pallidus and thalamus on T2-weighted images was also reported (78).

DW imaging is more sensitive than T2- and proton density-weighted imaging in detecting cortical abnormalities (79). Demaerel et al also report the changing pattern of cortical involvement, with new lesions appearing and existing lesions becoming less obvious in a short period of time (79). They suggest that patients with suspected CJD and no abnormalities on T2- and proton density-weighted images may have cortical involvement on DW images. The reported ADC values are normal or elevated (0.84 and 1.17 x 10^-3 mm²/sec in the study of Demaerel et al [79], 0.74–0.83 in a case we studied (Fig 30).