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Objective:
This study aims to describe the radiologic appearance of musculoskeletal ancient schwannoma with pathologic correlation.

Materials and Methods:
We retrospectively reviewed available demographics, imaging and pathologic material from 15 cases of pathologically proven musculoskeletal ancient schwannoma (schwannoma with prominent cystic degeneration or hemorrhagic/necrotic components) from our archives. Evaluation included patient demographics/history and lesion location/size. Radiologic evaluation was performed by two musculoskeletal radiologists and one fellow with agreement by consensus. Imaging radiographs (n = 1), PET/bone scintigraphy (n = 1), ultrasonography (US, n = 4, Doppler n = 1), CT (n = 4), MR (n = 13) was evaluated for location and intrinsic characteristics and was correlated with pathology when available.

Results:
Patients included 62% men and 38% women (average age 54.6 years; age range 30 - 83 years). Common locations were the lower extremity (40%), upper extremity (7%), mediastinal/paraspinal (13%), and retroperitoneum (40%). In the extremities, lesions were most commonly intermuscular in location (88%) or subcutaneous (12%). The masses were commonly well-defined, with a complete/incomplete pseudocapsule in 64% of cases and with ill-defined margins in only 36% on MR. The mass was intimately related to the affected nerve in 50% of cases. However, no growth up or down the affected nerve was seen in any of the cases. The lesions were frequently of lower attenuation than muscle on CT (75%), hypoechoic on US (67%), and on MRI predominantly low/intermediate signal on T1-weighting (70%), and very high signal on T2 weighting (62%). Enhancement after contrast (CT or MRI) was most commonly peripheral and nodular (62%) and mild/moderate in degree (88%). Areas of cystic degeneration/hemorrhage/necrosis were present in 85% on MR. Cystic degeneration/hemorrhage/necrosis comprised a prominent amount of the lesion in 67%of cases on CT and MR, with fluid levels present on MR in 40% of cases. Intimate relationship with a peripheral nerve (often a large nerve or exiting/entering nerve) was relatively frequent, seen in 60% of cases overall (80% on MRI). However, other imaging features frequently associated with benign peripheral nerve sheath tumors (PNST) were relatively uncommon such as fascicular sign (20%) and muscle atrophy (20%).

Conclusion:
Musculoskeletal ancient schwannoma can simulate malignant PNST and other sarcomas owing to their large size and areas of cystic degeneration/hemorrhage/necrosis on imaging evaluation. Features suggesting a PNST are present in 60% of cases overall and in 80% of cases on MRI (most frequently with an intimate relationship to an entering/exiting nerve). Lack of ill-defined margin and no growth up/down the involved nerve, as well as knowledge of this diagnosis, can aid in distinction from malignant PNST. Biopsy must be directed at the often smaller solid component for accurate pathologic diagnosis.