Presentation
Persistent left hip and groin pain after feeling a "pop" an experiencing sharp pain while exercising several weeks ago. The pain progressed over a couple of weeks to the point she can no longer walk.
Patient Data
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The left proximal femur has a well-defined lytic lesion with thin sclerotic margins, extending radially from the intertrochanteric region to involve the femoral neck, greater trochanter, and subtrochanteric region. A trans-cervical fracture line is present through this lesion, with some hypertrophic/buttressing bone at the fracture site medially.
The sacroliliac joints have sclerosis along their iliac margins bilaterally. Essure contraceptive coils are present.
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Re-demonstration of the findings seen on radiographs, showing a lytic lesion in the left proximal femur, with a well-defined sclerotic rim, but with multiple areas of severe cortical thinning and cortical violation, as well as homogeneous soft-tissue attenuation. The fracture line is also well characterized, extending through the remaining portion of the posterior cortex of the femoral neck.
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A lobulated lesion is present in the left femoral neck and intertrochanteric region, which is isointense to muscle on T1 and heterogeneously hyperintense on T2/STIR. A portion of this lesion extends beyond the osseous confines of the anterior and lateral femoral neck, up to 1cm, in the region that cortical violation was present on CT. A small amount of fluid-like signal (edema) extends along the adjacent intermuscular fascial planes. A small hip joint effusion is present. All other intraosseous marrow signal is normal, and no satellite lesions or enlarged lymph nodes are identified.
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Benign spindle cell neoplasm of neural/nerve origin.
Immunohistochemistry:
- Ki-67: <2%
- S-100: positive
Diagnosis: Pathologic changes indicate bone schwannoma.
Case Discussion
Intraosseous schwannomas are rare, representing <1% of primary bone tumors. They tend to occur in the mandible (arising from the inferior alveolar nerve), however can occur in almost any bone, and tend to occur in or near nutrient canals.
Radiographically, intraosseous schwannomas tend to present with benign, cyst-like features, and on MR they typically show features similar to those seen here, with isointense signal to muscle on T1 and heterogeneously hyperintense T2 signal. As these characteristics are not unique, predicting this histologic entity in the differential diagnosis is difficult, however should at least be considered in appropriate cases.
In the past, this entity has routinely been referred to as an intraosseous neurilemmoma.
Special thanks to Dr. Cristina Costales for the photomicrographs.
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