(Radiographics. 1999;19:1098-1101.)
© RSNA, 1999
Neuroradiology Case of the Day1
Francis G. Greiner, MD and
Deepak Takhtani, MD
1 From the Department of Radiology, University of South Alabama Medical Center, Mobile (F.G.G., D.T.), and the Department of Radiology, University of South Alabama School of Medicine, 2451 Fillingim St, Mobile, AL 36617 (F.G.G.). From the 1998 RSNA scientific assembly. Received January 18, 1999; revision requested February 2 and received March 1; accepted March 12. Address reprint requests to F.G.G.
Index Terms: Brain, blood flow, 176.76 • Brain, diseases, 176.75 • Brain, infarction, 176.78 • Sinuses, superior sagittal, 176.75, 176.78 Veins, thrombosis, 176.75
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HISTORY
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A 19-year-old woman presented with a 3-week history of headaches and blurred vision and with new onset of weakness on the right side. Computed tomography (CT), magnetic resonance (MR) imaging, and digital subtraction arteriography were performed.
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FINDINGS
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Unenhanced and contrast material–enhanced CT of the brain demonstrated low attenuation in the left parietal and right frontal areas (Fig 1). A filling defect was seen within the superior sagittal sinus. MR imaging performed several hours later demonstrated an absence of the normal flow void in the midline of the superior sagittal sinus (Fig 2a). Axial MR images showed a persistent flow void and evidence of infarct in the areas that appeared abnormal at CT (Fig 2b–2d). Contrast-enhanced T1-weighted MR images demonstrated irregular enhancement, prominent venous enhancement, and a filling defect in the superior sagittal sinus (Fig 2d, 2e). Venous-phase digital subtraction arteriography showed no filling of the straight or superior sagittal sinus, although the vein of Galen was well visualized (Fig 3).
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Figure 1a. (a) Axial CT scan of the brain reveals a subtle area of low attenuation in the right frontal area and a second, more obvious region in the left parietal lobe (arrows). (b) Contrast-enhanced CT scan obtained at the same level demonstrates an "empty delta sign" (arrowhead) with additional enhancement that is gyriform and probably venous (arrows).
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Figure 1b. (a) Axial CT scan of the brain reveals a subtle area of low attenuation in the right frontal area and a second, more obvious region in the left parietal lobe (arrows). (b) Contrast-enhanced CT scan obtained at the same level demonstrates an "empty delta sign" (arrowhead) with additional enhancement that is gyriform and probably venous (arrows).
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Figure 2a. (a) Sagittal MR image does not demonstrate the flow void normally seen in the superior sagittal sinus. Instead, there is an area of irregular intermediate signal intensity within the sinus (arrows). (b) Axial intermediate weighted MR image demonstrates increased subcortical and cortical signal intensity in the areas that appeared abnormal at CT, a finding consistent with stroke. (c) Axial T2-weighted MR images help confirm stroke. As in a and b, the sagittal sinus has low signal intensity. (d) Axial contrast-enhanced T1-weighted MR image demonstrates prominent venous enhancement as well as irregular enhancement in the areas of infarct and slow-flowing veins (arrows). The superior sagittal sinus does not demonstrate normal filling (arrowhead). (e) Coronal contrast-enhanced T1-weighted MR image reveals prominent enhancement of the left parietal lobe infarct and an empty delta sign in the superior sagittal sinus (arrow).
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Figure 2b. (a) Sagittal MR image does not demonstrate the flow void normally seen in the superior sagittal sinus. Instead, there is an area of irregular intermediate signal intensity within the sinus (arrows). (b) Axial intermediate weighted MR image demonstrates increased subcortical and cortical signal intensity in the areas that appeared abnormal at CT, a finding consistent with stroke. (c) Axial T2-weighted MR images help confirm stroke. As in a and b, the sagittal sinus has low signal intensity. (d) Axial contrast-enhanced T1-weighted MR image demonstrates prominent venous enhancement as well as irregular enhancement in the areas of infarct and slow-flowing veins (arrows). The superior sagittal sinus does not demonstrate normal filling (arrowhead). (e) Coronal contrast-enhanced T1-weighted MR image reveals prominent enhancement of the left parietal lobe infarct and an empty delta sign in the superior sagittal sinus (arrow).
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Figure 2c. (a) Sagittal MR image does not demonstrate the flow void normally seen in the superior sagittal sinus. Instead, there is an area of irregular intermediate signal intensity within the sinus (arrows). (b) Axial intermediate weighted MR image demonstrates increased subcortical and cortical signal intensity in the areas that appeared abnormal at CT, a finding consistent with stroke. (c) Axial T2-weighted MR images help confirm stroke. As in a and b, the sagittal sinus has low signal intensity. (d) Axial contrast-enhanced T1-weighted MR image demonstrates prominent venous enhancement as well as irregular enhancement in the areas of infarct and slow-flowing veins (arrows). The superior sagittal sinus does not demonstrate normal filling (arrowhead). (e) Coronal contrast-enhanced T1-weighted MR image reveals prominent enhancement of the left parietal lobe infarct and an empty delta sign in the superior sagittal sinus (arrow).
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Figure 2d. (a) Sagittal MR image does not demonstrate the flow void normally seen in the superior sagittal sinus. Instead, there is an area of irregular intermediate signal intensity within the sinus (arrows). (b) Axial intermediate weighted MR image demonstrates increased subcortical and cortical signal intensity in the areas that appeared abnormal at CT, a finding consistent with stroke. (c) Axial T2-weighted MR images help confirm stroke. As in a and b, the sagittal sinus has low signal intensity. (d) Axial contrast-enhanced T1-weighted MR image demonstrates prominent venous enhancement as well as irregular enhancement in the areas of infarct and slow-flowing veins (arrows). The superior sagittal sinus does not demonstrate normal filling (arrowhead). (e) Coronal contrast-enhanced T1-weighted MR image reveals prominent enhancement of the left parietal lobe infarct and an empty delta sign in the superior sagittal sinus (arrow).
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Figure 2e. (a) Sagittal MR image does not demonstrate the flow void normally seen in the superior sagittal sinus. Instead, there is an area of irregular intermediate signal intensity within the sinus (arrows). (b) Axial intermediate weighted MR image demonstrates increased subcortical and cortical signal intensity in the areas that appeared abnormal at CT, a finding consistent with stroke. (c) Axial T2-weighted MR images help confirm stroke. As in a and b, the sagittal sinus has low signal intensity. (d) Axial contrast-enhanced T1-weighted MR image demonstrates prominent venous enhancement as well as irregular enhancement in the areas of infarct and slow-flowing veins (arrows). The superior sagittal sinus does not demonstrate normal filling (arrowhead). (e) Coronal contrast-enhanced T1-weighted MR image reveals prominent enhancement of the left parietal lobe infarct and an empty delta sign in the superior sagittal sinus (arrow).
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Figure 3. On a venous-phase digital substraction angiogram, the superior sagittal sinus demonstrates no filling (arrowheads). The vein of Galen demonstrates normal filling (arrow), whereas the straight sinus demonstrates only minimal filling, a finding consistent with thrombosis.
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DIAGNOSIS: Superior sagittal sinus thrombosis and infarcts.
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DISCUSSION
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The superior sagittal sinus is a midline venous channel located between the inner and outer dural laminae. It receives blood from many tributaries, including the cortical cerebral, meningeal, emissary, and scalp veins. The meningeal veins drain to lateral venous lacunae, which then form a chain of venous cavities on both sides of the superior sagittal sinus. These channels can provide a collateral drainage pathway that bypasses the thrombosis of the superior sagittal sinus (1).
Many predisposing factors have been implicated in the development of dural sinus thrombosis. Trauma, infection, tumors, dehydration, pregnancy, oral contraceptives, and hypercoagulable states are the most common causes of dural sinus thrombosis. Unusual causes of dural sinus thrombosis include Behçet disease, acquired immunodeficiency syndrome, ulcerative colitis, chemotherapy (particularly with asparaginase and cytarabine), the blastic crisis of chronic myelogenous leukemia, lupus (systemic lupus erythematosus), nephrotic syndrome, and jugular vein catheterization. An association of dural sinus thrombosis with pulmonary thromboembolism has also been described. In addition, dural sinus thrombosis is associated with congenital heart disease, antithrombin III deficiency, protein C resistance, protein S disease, and antiphospholipid syndrome. Nearly 20% of cases of dural sinus thrombosis are idiopathic. The mortality rate associated with this disease entity can be as high as 10%–30% (1–5).
Dural sinus thrombosis manifests with diverse clinical findings. Early symptoms often include headaches and lethargy. As the disease progresses, seizures, decreased mentation, focal deficits, and obtundation can occur. Strokes (often hemorrhagic) may develop secondary to poor venous drainage and increased intracranial pressure. These strokes are often bilateral and outside the normal arterial distribution, reflecting the different pattern of venous drainage. Quite often, the thrombosis has developed several days before the onset of symptoms (2,6).
Veno-occlusive disease of the brain most commonly affects the superior sagittal sinus, followed by the transverse, sigmoid, and straight sinuses. Dural sinus thrombosis leads to venous congestion, brain edema, and sulcal effacement. Hydrocephalus has been noted in some cases and is probably the result of decreased absorption of cerebrospinal fluid due to elevated dural pressure and altered cerebrospinal fluid flow dynamics.
Imaging findings in dural sinus thrombosis can be conveniently grouped into those related to (a) intraluminal thrombus (eg, empty delta sign, "cord sign"), (b) venous collateral flow, (eg, gyral and tentorial enhancement), (c) brain involvement (eg, hemorrhage, infarcts, edema), and (d) changes in flow dynamics, which are most evident at MR imaging (1).
CT, MR imaging, conventional angiography, and, more recently, CT venography have been used to detect dural sinus thrombosis. Unenhanced CT may demonstrate increased attenuation in thrombosed veins (cord sign) (7,8). This finding may be present in only 20% of cases and is nonspecific. After administration of contrast material, CT may demonstrate enhanced venous structures (Fig 1b) or enlargement of the thrombosed veins near the obstruction. The veins may become "shaggy" and irregular as small collateral vessels near the obstructed veins enhance.
The empty delta sign occurs when the thrombus fails to enhance within the dural sinus and is outlined by enhanced collateral channels in the falx. This sign is seen in only about 25%–30% of cases but is highly diagnostic for sagittal sinus thrombosis (1,7). False-positive causes of the empty delta sign include subdural hematoma, subdural empyema, and arachnoid granulations. If sagittal sinus thrombosis is suspected, one should look for outward bowing of the superior sagittal sinus wall, which is an abnormal finding. False-negative empty delta signs result from partial volume averaging effects, a small thrombus, or recanalized thrombus (8). Other nonspecific signs include reduced ventricular size secondary to increased intracranial pressure, subdural collections, and stroke (1,2).
MR imaging has several advantages over CT in the detection of sinus thrombosis. The flow voids routinely seen in the large veins and sinuses make visualization of venous thrombosis easier. The orthogonal planes routinely used also aid in identification of the abnormal areas. In late and chronic sinus thrombosis, the clot will demonstrate bright signal from methemoglobin with both T1- and T2-weighted sequences and will be readily visible (9).
The appearance of acute thrombus is somewhat more difficult to demonstrate at MR imaging. In hyperacute thrombosis, the clot has low signal intensity on both T1- and T2-weighted MR images. The effect is more pronounced on T2-weighted images; T1-weighted images may show low signal intensity rather than the normal flow void (Fig 2a). This effect can be complicated by flow-related enhancement, which may cause an increase in signal intensity on entry sections (10). At 3 weeks, the clot may have low signal with all sequences and may later recanalize with or without residual thrombus signal (11–14).
MR venography has been found to be reliable in the diagnosis of dural sinus thrombosis but is susceptible to error in cases involving velocity-encoding mismatch or slow flow (10). Direct signs of dural sinus thrombosis at MR venography include loss of vascular flow signal or a frayed appearance of the venous sinus. Indirect signs of thrombosis include the presence of collateral flow from extracranial vessels and prominent flow signal from the deeper medullary veins. Increased intracranial pressure can be indicated by visualization of the arterial system with a gradient-echo sequence despite presaturation at the carotid bifurcation (14,15). More recently, CT venography has shown promise in diagnosing dural sinus thrombosis and has been found to have a sensitivity equal to that of MR venography (16).
Treatment for dural sinus thrombosis generally involves heparin therapy, with over 70% of patients experiencing nearly full recovery. In individuals who are refractory to heparin therapy, direct lysis of the thrombosed sinus has been performed with the venous and direct puncture approach (6,17–19). Our patient underwent heparin therapy with recanalization of the sinus but experienced persistent right-sided weakness and stroke deficit.
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References
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HISTORY
FINDINGS
