[110] Schwannoma of Bone: A Clinicopathologic and Radiologic Study

BW Scheithauer, CM Ida, O Yapicier, JA Carney, DE Wenger, CY Inwards, F Bertoni, RJ Spinner, KK Unni. Mayo Clinic, Rochester, MN; Istituto Ortopedico Rizzoli, Bologna, Italy

Background: Schwannoma of bone is a rare neoplasm occuring most commonly in the jaws,temporal bone and sacrum. Although apparently arising in bone, they actually arise from nerves traversing bone within intraosseous foramina. Herein, we characterize the clinicopathologic features of 17 schwannomas originating within the substance of bone and radiologically mimicking other, more frequent primary bone tumors.
Design: Of 217 schwannomas involving bone and either operated at our Institution or seen in consultation between the years of 1974 to 2004, 17 were apparently primary in bone. Tumors excluded were a) situated in soft tissue and causing secondary bone erosion or b) within nerve foramina of the jaws, temporal bone or sacrum, and c) lesions histologically reclassified. Immunohistochemical studies directed against S-100 protein, collagen IV, HMB-45, Melan A and Ki-67 antigen were performed.
Results: In our series, schwannomas of bone represented 1% of primary bone tumors seen over a 30 year-period. Median patient age was 40 yrs (range, 9-56), with a slight female predilection (F:M=1:0.7). Long bones (71%), particularly the diaphysial region, were most often affected. Pain was the most frequent complaint. Of the 17 lesions, 13 were conventional schwannomas, two with degenerative atypia (ancient schwannoma), 1 was cellular and 3 were melanotic, 2 being psammomatous. Aside from the 2 psammomatous melanotic schwannomas that occurred in Carney complex, the remaining lesions were solitary and sporadic having no association with neurofibromatosis or schwannomatosis. Mitoses ranged from 0 to 2 /10HPF. No necrosis was observed. Immunostaining included S-100 protein and pericellular collagen IV in all tumors tested. MIB1 index was uniformly low. All melanotic tumors were also immunoreactive for HMB45 and Melan A. Follow-up information was available in 11 cases (64%) and ranged from 4 to 19 yrs. One conventional schwanoma recurred at 4 yrs; the patient is tumor-free at 9 yrs. No patient developed metastases or died of disease.
Conclusions: As schwannoma of bone is rare, it is often not included in the differential diagnosis of primary osseous spindle cell tumors. Awareness of its occurrence, particularly of the cellular and melanotic variants should preclude histologic misdiagnosis and overtreatment. Like their far more common extraosseous counterparts, schwannoma of bone behaves in a benign fashion and is successfully treated by local excision alone.
Category: Bone & Soft Tissue

Monday, March 22, 2010 1:00 PM

Poster Session II # 4, Monday Afternoon


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