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DOI: 10.1148/rg.273065031
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Pitfalls in MR Image Interpretation Prompting Referrals to an Orthopedic Oncology Clinic1

Gregory Scott Stacy, MD and Larry B. Dixon, MD

1 From the Department of Radiology, University of Chicago Hospitals, 5841 S Maryland Ave, MC 2026, Chicago, IL 60637. Recipient of a Certificate of Merit award for an education exhibit at the 2005 RSNA Annual Meeting. Received March 17, 2006; revision requested August 14 and received August 25; accepted August 28. Authors have no financial relationships to disclose.

Figure 1A
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  		Figure 1a.  Normal hematopoietic (or red) marrow in a 21-year-old woman with knee pain and no additional medical problems. (a) Coronal T1-weighted MR image shows patchy regions of intermediate signal intensity (arrows) in the distal femur. These regions have signal intensity higher than that in nearby skeletal muscle (*), and this characteristic is suggestive of residual red marrow. (b) Coronal T2-weighted fat-suppressed MR image shows a patchy area (arrow) with signal intensity similar to that of skeletal muscle (*). MR images from 1%–2% of patients referred to the Orthopaedic Oncology Clinic showed similar features that are characteristic of residual red marrow but that were misinterpreted as potential malignancy.

 

Figure 1B
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  		Figure 1b.  Normal hematopoietic (or red) marrow in a 21-year-old woman with knee pain and no additional medical problems. (a) Coronal T1-weighted MR image shows patchy regions of intermediate signal intensity (arrows) in the distal femur. These regions have signal intensity higher than that in nearby skeletal muscle (*), and this characteristic is suggestive of residual red marrow. (b) Coronal T2-weighted fat-suppressed MR image shows a patchy area (arrow) with signal intensity similar to that of skeletal muscle (*). MR images from 1%–2% of patients referred to the Orthopaedic Oncology Clinic showed similar features that are characteristic of residual red marrow but that were misinterpreted as potential malignancy.

 

Figure 2A
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  		Figure 2a.  Fatigue fracture in a 25-year-old woman runner with low back pain. Coronal T1-weighted (a) and coronal T2-weighted fat-suppressed (b) MR images show edema in the left sacral ala as well as a linear band (arrow) that extends through the region of edema, a typical finding of stress fracture. MR images from nearly 2% of patients referred to the Orthopaedic Oncology Clinic showed features characteristic of stress fracture or stress reaction that were misinterpreted as a potential malignancy.

 

Figure 2B
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  		Figure 2b.  Fatigue fracture in a 25-year-old woman runner with low back pain. Coronal T1-weighted (a) and coronal T2-weighted fat-suppressed (b) MR images show edema in the left sacral ala as well as a linear band (arrow) that extends through the region of edema, a typical finding of stress fracture. MR images from nearly 2% of patients referred to the Orthopaedic Oncology Clinic showed features characteristic of stress fracture or stress reaction that were misinterpreted as a potential malignancy.

 

Figure 3A
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  		Figure 3a.  Metatarsal stress fracture in a 53-year-old woman with forefoot pain. (a) Short-axis T1-weighted fat-suppressed MR image, obtained after the intravenous administration of a gadolinium chelate, shows enhancement of the marrow of the fourth metatarsal (arrowhead) as well as the surrounding soft tissues (arrow). (b) Sagittal T1-weighted MR image shows mild and poorly defined low-signal-intensity edema (arrowhead) in the marrow of the distal fourth metatarsal, with a slight angulation of the dorsal cortex (arrow), findings suggestive of a stress fracture. Follow-up radiographs (not shown) revealed callus formation at the site, a finding that helped confirm the diagnosis. Stress fractures and stress reaction often result in relatively mild marrow edema on T1-weighted images, compared with more pronounced marrow and soft-tissue edema on T2-weighted images. Marrow and soft-tissue enhancement after gadolinium administration also is fairly common.

 

Figure 3B
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  		Figure 3b.  Metatarsal stress fracture in a 53-year-old woman with forefoot pain. (a) Short-axis T1-weighted fat-suppressed MR image, obtained after the intravenous administration of a gadolinium chelate, shows enhancement of the marrow of the fourth metatarsal (arrowhead) as well as the surrounding soft tissues (arrow). (b) Sagittal T1-weighted MR image shows mild and poorly defined low-signal-intensity edema (arrowhead) in the marrow of the distal fourth metatarsal, with a slight angulation of the dorsal cortex (arrow), findings suggestive of a stress fracture. Follow-up radiographs (not shown) revealed callus formation at the site, a finding that helped confirm the diagnosis. Stress fractures and stress reaction often result in relatively mild marrow edema on T1-weighted images, compared with more pronounced marrow and soft-tissue edema on T2-weighted images. Marrow and soft-tissue enhancement after gadolinium administration also is fairly common.

 

Figure 4A
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  		Figure 4a.  Myelodysplastic syndrome in a 43-year-old woman with ankle pain. (a) Lateral ankle radiograph shows a poorly defined region of lucency (arrowheads) centrally within the distal tibia. (b) Sagittal T1-weighted MR image shows a curvilinear band of low signal intensity (arrowhead) that surrounds a central region of fat signal intensity (*). (c) Sagittal T2-weighted fat-suppressed MR image shows a high-signal-intensity curvilinear band that surrounds a low-signal-intensity central region of necrotic bone. Note the double line sign (arrow), a feature that is virtually pathognomonic of osteonecrosis. Images from 2%–3% of patients referred to the Orthopaedic Oncology Clinic showed findings characteristic of osteonecrosis but interpreted as potential malignancy. MR imaging should allow a confident diagnosis in most cases.

 

Figure 4B
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  		Figure 4b.  Myelodysplastic syndrome in a 43-year-old woman with ankle pain. (a) Lateral ankle radiograph shows a poorly defined region of lucency (arrowheads) centrally within the distal tibia. (b) Sagittal T1-weighted MR image shows a curvilinear band of low signal intensity (arrowhead) that surrounds a central region of fat signal intensity (*). (c) Sagittal T2-weighted fat-suppressed MR image shows a high-signal-intensity curvilinear band that surrounds a low-signal-intensity central region of necrotic bone. Note the double line sign (arrow), a feature that is virtually pathognomonic of osteonecrosis. Images from 2%–3% of patients referred to the Orthopaedic Oncology Clinic showed findings characteristic of osteonecrosis but interpreted as potential malignancy. MR imaging should allow a confident diagnosis in most cases.

 

Figure 4C
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  		Figure 4c.  Myelodysplastic syndrome in a 43-year-old woman with ankle pain. (a) Lateral ankle radiograph shows a poorly defined region of lucency (arrowheads) centrally within the distal tibia. (b) Sagittal T1-weighted MR image shows a curvilinear band of low signal intensity (arrowhead) that surrounds a central region of fat signal intensity (*). (c) Sagittal T2-weighted fat-suppressed MR image shows a high-signal-intensity curvilinear band that surrounds a low-signal-intensity central region of necrotic bone. Note the double line sign (arrow), a feature that is virtually pathognomonic of osteonecrosis. Images from 2%–3% of patients referred to the Orthopaedic Oncology Clinic showed findings characteristic of osteonecrosis but interpreted as potential malignancy. MR imaging should allow a confident diagnosis in most cases.

 

Figure 5
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  		Figure 5.  Sarcomatous degeneration of bone in a 57-year-old man with right knee pain that did not respond to physical therapy. Anteroposterior radiograph of the knee shows sclerotic lesions typical of multifocal osteonecrosis (arrowheads). Destruction of the lateral cortex of the proximal tibia (arrow) is indicative of sarcomatous degeneration, a finding that was confirmed at MR imaging. This patient was appropriately referred to the Orthopaedic Oncology Clinic.

 

Figure 6
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  		Figure 6.  Paget disease of bone in a 64-year-old woman. Lateral radiograph of the distal forearm shows the advancing lytic front typical of the "active" phase of disease (arrowhead) and cortical and trabecular thickening characteristic of the "sclerotic" phase (arrow), as well as bowing and generalized expansile remodeling of the distal radius. Patients with images that showed characteristic features of Paget disease in unusual locations (eg, bones of the upper extremity) occasionally were referred to the Orthopaedic Oncology Clinic with a presumptive diagnosis of neoplasm.

 

Figure 7A
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  		Figure 7a.  Paget disease of bone in a 50-year-old woman. (a) Axial T1-weighted MR image of the pelvis shows abnormally low-signal-intensity marrow in the left ilium (arrowhead) and thickened cortex (arrow). (b) Axial CT image of the pelvis better illustrates the cortical thickening (arrow), a finding typical of Paget disease. Approximately 1% of patients referred to the Orthopaedic Oncology Clinic had abnormalities at MR imaging that could have been easily diagnosed as Paget disease at radiography or CT.

 

Figure 7B
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  		Figure 7b.  Paget disease of bone in a 50-year-old woman. (a) Axial T1-weighted MR image of the pelvis shows abnormally low-signal-intensity marrow in the left ilium (arrowhead) and thickened cortex (arrow). (b) Axial CT image of the pelvis better illustrates the cortical thickening (arrow), a finding typical of Paget disease. Approximately 1% of patients referred to the Orthopaedic Oncology Clinic had abnormalities at MR imaging that could have been easily diagnosed as Paget disease at radiography or CT.

 

Figure 8A
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  		Figure 8a.  Fibroxanthoma (nonossifying fibroma) in a 16-year-old girl. (a) Lateral radiograph of the knee shows a mixed lucent and sclerotic intramedullary lesion (arrowheads) along the posterior cortex of the distal femur. The sclerotic margin and multilocular appearance are typical of a fibroxanthoma. (b) Sagittal T2-weighted MR image of the knee shows areas of heterogeneous signal intensity (arrowheads) within the lesion. Images from 2%–3% of patients referred to the Orthopaedic Oncology Clinic showed features characteristic of fibroxanthoma but interpreted as a potential malignancy. Several of these patients arrived with only MR images and probably would not have been referred if a radiograph had been obtained for correlation.

 

Figure 8B
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  		Figure 8b.  Fibroxanthoma (nonossifying fibroma) in a 16-year-old girl. (a) Lateral radiograph of the knee shows a mixed lucent and sclerotic intramedullary lesion (arrowheads) along the posterior cortex of the distal femur. The sclerotic margin and multilocular appearance are typical of a fibroxanthoma. (b) Sagittal T2-weighted MR image of the knee shows areas of heterogeneous signal intensity (arrowheads) within the lesion. Images from 2%–3% of patients referred to the Orthopaedic Oncology Clinic showed features characteristic of fibroxanthoma but interpreted as a potential malignancy. Several of these patients arrived with only MR images and probably would not have been referred if a radiograph had been obtained for correlation.

 

Figure 9
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  		Figure 9.  Enchondroma in a 40-year-old woman. Coronal T1-weighted MR image of the knee shows a small lobulated lesion (arrow) in the medullary cavity of the proximal tibia, a typical appearance of a benign enchondroma. Patients with a small, painless, lobulated lesion such as this need not be referred to an orthopedic oncologist.

 

Figure 10
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  		Figure 10.  Rheumatoid arthritis in a 61-year-old man. Coronal T2-weighted fat-suppressed image of the ankle shows a high-signal-intensity lesion with a surrounding hypointense rim (large arrow) in the inferior aspect of the talar body, features that represent an area of subcortical erosion with adjacent bone marrow edema. Several smaller areas of erosion in the calcaneus (small arrows) and high-signal-intensity synovitis in the tarsal sinus (*) support a diagnosis of erosive inflammatory arthritis rather than a neoplasm. Subchondral erosions and degenerative cysts, particularly larger (1–3-cm) lesions with adjacent edema and enhancement, were commonly misinterpreted as a neoplasm and resulted in needless referrals to the Orthopaedic Oncology Clinic. This case demonstrates the importance of recognizing an arthritic process.

 

Figure 11A
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  		Figure 11a.  Popliteal cyst with ossified loose bodies in a 64-year-old woman. (a) Sagittal T2-weighted MR image of the knee shows an apparent mass with small internal foci of low signal intensity (arrowhead) posterior to the medial femoral condyle. (b) Axial intermediate-weighted fat-suppressed MR image shows round foci of low signal intensity (arrowhead) in the popliteal cyst. The "neck" of the cyst extends between the tendons of the semi-membranosus muscle (small arrow) and the medial head of the gastrocnemius muscle (large arrow). (c) Lateral radiograph shows ossified loose bodies (arrow) that correspond to the round low-signal-intensity foci seen on MR images. This case emphasizes the importance of knowing the bursal anatomy and correlating MR images with radiographs.

 

Figure 11B
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  		Figure 11b.  Popliteal cyst with ossified loose bodies in a 64-year-old woman. (a) Sagittal T2-weighted MR image of the knee shows an apparent mass with small internal foci of low signal intensity (arrowhead) posterior to the medial femoral condyle. (b) Axial intermediate-weighted fat-suppressed MR image shows round foci of low signal intensity (arrowhead) in the popliteal cyst. The "neck" of the cyst extends between the tendons of the semi-membranosus muscle (small arrow) and the medial head of the gastrocnemius muscle (large arrow). (c) Lateral radiograph shows ossified loose bodies (arrow) that correspond to the round low-signal-intensity foci seen on MR images. This case emphasizes the importance of knowing the bursal anatomy and correlating MR images with radiographs.

 

Figure 11C
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  		Figure 11c.  Popliteal cyst with ossified loose bodies in a 64-year-old woman. (a) Sagittal T2-weighted MR image of the knee shows an apparent mass with small internal foci of low signal intensity (arrowhead) posterior to the medial femoral condyle. (b) Axial intermediate-weighted fat-suppressed MR image shows round foci of low signal intensity (arrowhead) in the popliteal cyst. The "neck" of the cyst extends between the tendons of the semi-membranosus muscle (small arrow) and the medial head of the gastrocnemius muscle (large arrow). (c) Lateral radiograph shows ossified loose bodies (arrow) that correspond to the round low-signal-intensity foci seen on MR images. This case emphasizes the importance of knowing the bursal anatomy and correlating MR images with radiographs.

 

Figure 12A
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  		Figure 12a.  Ganglion of the Guyon canal in a 38-year-old man. (a) Axial T2-weighted MR image of the wrist shows a lobulated homogeneous mass (arrowhead) with fluid signal intensity volar to the hook of the hamate. (b) Axial T1-weighted fat-suppressed image of the wrist after intravenous administration of a gadolinium chelate shows only peripheral enhancement of the mass (arrowhead), a feature typical of a ganglion. Nearly 2% of patients referred to the Orthopaedic Oncology Clinic arrived with MR images that showed characteristic features of a juxta-articular cyst or ganglion that was misinterpreted as a potential malignancy. The signal intensity and enhancement patterns usually allow a confident diagnosis.

 

Figure 12B
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  		Figure 12b.  Ganglion of the Guyon canal in a 38-year-old man. (a) Axial T2-weighted MR image of the wrist shows a lobulated homogeneous mass (arrowhead) with fluid signal intensity volar to the hook of the hamate. (b) Axial T1-weighted fat-suppressed image of the wrist after intravenous administration of a gadolinium chelate shows only peripheral enhancement of the mass (arrowhead), a feature typical of a ganglion. Nearly 2% of patients referred to the Orthopaedic Oncology Clinic arrived with MR images that showed characteristic features of a juxta-articular cyst or ganglion that was misinterpreted as a potential malignancy. The signal intensity and enhancement patterns usually allow a confident diagnosis.

 

Figure 13A
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  		Figure 13a.  Synovial sarcoma in an 18-year-old man. (a) Axial T2-weighted fat-suppressed MR image of the knee shows a relatively homogeneously hyperintense mass (arrowhead) deep to the medial retinaculum. The mass mimics a large cyst. (b) Axial T1-weighted fat-suppressed MR image of the knee, obtained after the intravenous administration of a gadolinium chelate, shows diffuse enhancement of the mass (arrowhead), a finding indicative of a solid tumor. This patient was appropriately referred to the Orthopaedic Oncology Clinic.

 

Figure 13B
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  		Figure 13b.  Synovial sarcoma in an 18-year-old man. (a) Axial T2-weighted fat-suppressed MR image of the knee shows a relatively homogeneously hyperintense mass (arrowhead) deep to the medial retinaculum. The mass mimics a large cyst. (b) Axial T1-weighted fat-suppressed MR image of the knee, obtained after the intravenous administration of a gadolinium chelate, shows diffuse enhancement of the mass (arrowhead), a finding indicative of a solid tumor. This patient was appropriately referred to the Orthopaedic Oncology Clinic.

 

Figure 14A
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  		Figure 14a.  Muscle strain injury in a 20-year-old man. (a) Axial T2-weighted MR image of the thigh shows a mass with high signal intensity (arrowhead) within the rectus femoris. (b) Axial T1-weighted MR image shows the location of the high-signal-intensity mass (arrowhead) adjacent to the distal tendon (arrow) of the rectus femoris muscle, findings compatible with a subacute hematoma from a previous myotendinous strain injury. The low-signal-intensity rim that partially surrounds the hematoma represents hemosiderin deposition. Knowledge of the MR imaging appearance of hematomas should allow the avoidance of a mistaken diagnosis of malignancy in most cases.

 

Figure 14B
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  		Figure 14b.  Muscle strain injury in a 20-year-old man. (a) Axial T2-weighted MR image of the thigh shows a mass with high signal intensity (arrowhead) within the rectus femoris. (b) Axial T1-weighted MR image shows the location of the high-signal-intensity mass (arrowhead) adjacent to the distal tendon (arrow) of the rectus femoris muscle, findings compatible with a subacute hematoma from a previous myotendinous strain injury. The low-signal-intensity rim that partially surrounds the hematoma represents hemosiderin deposition. Knowledge of the MR imaging appearance of hematomas should allow the avoidance of a mistaken diagnosis of malignancy in most cases.

 

Figure 15A
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  		Figure 15a.  Avulsion injury and tendon retraction in a 58-year-old woman. (a) Axial T2-weighted MR image of the proximal thigh shows an apparent mass with a rim of high signal intensity (arrowhead) in the posterior soft tissues. Note the absence of the normal hamstring musculature. (b) Coronal T2-weighted fat-suppressed MR image shows the retracted hamstring musculature surrounded by fluid (arrowhead).

 

Figure 15B
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  		Figure 15b.  Avulsion injury and tendon retraction in a 58-year-old woman. (a) Axial T2-weighted MR image of the proximal thigh shows an apparent mass with a rim of high signal intensity (arrowhead) in the posterior soft tissues. Note the absence of the normal hamstring musculature. (b) Coronal T2-weighted fat-suppressed MR image shows the retracted hamstring musculature surrounded by fluid (arrowhead).

 

Figure 16A
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  		Figure 16a.  Avulsion injury in a 15-year-old boy. (a) Anteroposterior radiograph of the right hip shows lobulated ossification (arrow) along the proximal ischium. (b) Coronal T2-weighted MR image of the pelvis shows high-signal-intensity edema within the right ischium (arrowhead) as well as at the origin of the hamstring musculature (arrow). (c) Transverse CT image through the pelvis shows an avulsion fracture (arrowhead) arising from the right ischium at the hamstring origin. Healing avulsion injuries in children may mimic an ossifying neoplasm on radiographs; MR imaging or CT may be useful for follow-up evaluation.

 

Figure 16B
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  		Figure 16b.  Avulsion injury in a 15-year-old boy. (a) Anteroposterior radiograph of the right hip shows lobulated ossification (arrow) along the proximal ischium. (b) Coronal T2-weighted MR image of the pelvis shows high-signal-intensity edema within the right ischium (arrowhead) as well as at the origin of the hamstring musculature (arrow). (c) Transverse CT image through the pelvis shows an avulsion fracture (arrowhead) arising from the right ischium at the hamstring origin. Healing avulsion injuries in children may mimic an ossifying neoplasm on radiographs; MR imaging or CT may be useful for follow-up evaluation.

 

Figure 16C
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  		Figure 16c.  Avulsion injury in a 15-year-old boy. (a) Anteroposterior radiograph of the right hip shows lobulated ossification (arrow) along the proximal ischium. (b) Coronal T2-weighted MR image of the pelvis shows high-signal-intensity edema within the right ischium (arrowhead) as well as at the origin of the hamstring musculature (arrow). (c) Transverse CT image through the pelvis shows an avulsion fracture (arrowhead) arising from the right ischium at the hamstring origin. Healing avulsion injuries in children may mimic an ossifying neoplasm on radiographs; MR imaging or CT may be useful for follow-up evaluation.

 

Figure 17A
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  		Figure 17a.  Posttraumatic heterotopic ossification in a 15-year-old boy. (a) Anteroposterior radiograph of the left hip shows soft-tissue ossification (arrows) overlying the superolateral acetabulum and proximal femur. (b) Axial T1-weighted MR image of the hip shows a mass (arrowhead) of heterogeneous signal intensity in the approximate location of the rectus femoris muscle. (c) Axial T2-weighted MR image reveals that the mass (arrowhead) is of heterogeneously high signal intensity. (d) Axial T1-weighted MR image obtained after the intravenous administration of a gadolinium chelate shows enhancement of the mass (arrowhead). (e) Axial CT image reveals peripheral ossification of the mass (arrowhead), a typical feature of myositis ossificans traumatica. Myositis ossificans may mimic a soft-tissue sarcoma on MR images, but CT often reveals the true nature of the mass.

 

Figure 17B
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  		Figure 17b.  Posttraumatic heterotopic ossification in a 15-year-old boy. (a) Anteroposterior radiograph of the left hip shows soft-tissue ossification (arrows) overlying the superolateral acetabulum and proximal femur. (b) Axial T1-weighted MR image of the hip shows a mass (arrowhead) of heterogeneous signal intensity in the approximate location of the rectus femoris muscle. (c) Axial T2-weighted MR image reveals that the mass (arrowhead) is of heterogeneously high signal intensity. (d) Axial T1-weighted MR image obtained after the intravenous administration of a gadolinium chelate shows enhancement of the mass (arrowhead). (e) Axial CT image reveals peripheral ossification of the mass (arrowhead), a typical feature of myositis ossificans traumatica. Myositis ossificans may mimic a soft-tissue sarcoma on MR images, but CT often reveals the true nature of the mass.

 

Figure 17C
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  		Figure 17c.  Posttraumatic heterotopic ossification in a 15-year-old boy. (a) Anteroposterior radiograph of the left hip shows soft-tissue ossification (arrows) overlying the superolateral acetabulum and proximal femur. (b) Axial T1-weighted MR image of the hip shows a mass (arrowhead) of heterogeneous signal intensity in the approximate location of the rectus femoris muscle. (c) Axial T2-weighted MR image reveals that the mass (arrowhead) is of heterogeneously high signal intensity. (d) Axial T1-weighted MR image obtained after the intravenous administration of a gadolinium chelate shows enhancement of the mass (arrowhead). (e) Axial CT image reveals peripheral ossification of the mass (arrowhead), a typical feature of myositis ossificans traumatica. Myositis ossificans may mimic a soft-tissue sarcoma on MR images, but CT often reveals the true nature of the mass.

 

Figure 17D
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  		Figure 17d.  Posttraumatic heterotopic ossification in a 15-year-old boy. (a) Anteroposterior radiograph of the left hip shows soft-tissue ossification (arrows) overlying the superolateral acetabulum and proximal femur. (b) Axial T1-weighted MR image of the hip shows a mass (arrowhead) of heterogeneous signal intensity in the approximate location of the rectus femoris muscle. (c) Axial T2-weighted MR image reveals that the mass (arrowhead) is of heterogeneously high signal intensity. (d) Axial T1-weighted MR image obtained after the intravenous administration of a gadolinium chelate shows enhancement of the mass (arrowhead). (e) Axial CT image reveals peripheral ossification of the mass (arrowhead), a typical feature of myositis ossificans traumatica. Myositis ossificans may mimic a soft-tissue sarcoma on MR images, but CT often reveals the true nature of the mass.

 

Figure 17E
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  		Figure 17e.  Posttraumatic heterotopic ossification in a 15-year-old boy. (a) Anteroposterior radiograph of the left hip shows soft-tissue ossification (arrows) overlying the superolateral acetabulum and proximal femur. (b) Axial T1-weighted MR image of the hip shows a mass (arrowhead) of heterogeneous signal intensity in the approximate location of the rectus femoris muscle. (c) Axial T2-weighted MR image reveals that the mass (arrowhead) is of heterogeneously high signal intensity. (d) Axial T1-weighted MR image obtained after the intravenous administration of a gadolinium chelate shows enhancement of the mass (arrowhead). (e) Axial CT image reveals peripheral ossification of the mass (arrowhead), a typical feature of myositis ossificans traumatica. Myositis ossificans may mimic a soft-tissue sarcoma on MR images, but CT often reveals the true nature of the mass.

 

Figure 18A
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  		Figure 18a.  Inflammatory myopathy in a 39-year-old man. (a) Axial T1-weighted fat-suppressed MR image of the arm shows enhancement of the brachialis muscle (arrowhead), a finding that mimics a mass. (b) Sagittal T1-weighted fat-suppressed MR image shows diffuse enhancement of the distal brachialis muscle (arrowheads); the muscle maintains its normal contour, and no mass is evident, two features that oppose a diagnosis of neoplasm. Muscle injury may have a similar appearance on MR images.

 

Figure 18B
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  		Figure 18b.  Inflammatory myopathy in a 39-year-old man. (a) Axial T1-weighted fat-suppressed MR image of the arm shows enhancement of the brachialis muscle (arrowhead), a finding that mimics a mass. (b) Sagittal T1-weighted fat-suppressed MR image shows diffuse enhancement of the distal brachialis muscle (arrowheads); the muscle maintains its normal contour, and no mass is evident, two features that oppose a diagnosis of neoplasm. Muscle injury may have a similar appearance on MR images.

 

Figure 19
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  		Figure 19.  Lipoma in a 49-year-old woman. Axial T1-weighted MR image shows a mass (arrowhead) in the musculature of the medial aspect of the right arm. The mass had homogeneous signal intensity characteristic of fat on all MR images, a finding indicative of a lipoma. Liposarcoma should not be included in the differential diagnosis.

 

Figure 20
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  		Figure 20.  Well-differentiated liposarcoma in a 63-year-old woman. Axial T1-weighted MR image of the arm shows a predominantly fatty mass (arrowhead) with prominent septa. Focal areas with signal that is slightly hypointense to that of fat are indicative of nonadipose elements (*). Although such findings might be representative also of a benign lipoma with nonadipose elements, referral to an orthopedic oncologist is appropriate.

 




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