[50] Hybrid Schwannoma/Perineurioma: Analysis of 39 Distinctive Benign Nerve Sheath Tumors

JL Hornick, EA Bundock, CDM Fletcher. Brigham & Women's Hospital, Harvard Medical School, Boston, MA

Background: Several years ago, our group presented a small series of benign nerve sheath tumors showing hybrid features of schwannoma and soft tissue perineurioma. The purpose of this study was to further characterize a large series of these lesions.
Design: 39 cases received between 1994 and 2008 were retrieved from authors' consult and surgical pathology files. Clinical details and follow-up were obtained from referring pathologists. H&E sections were re-examined, and immunohistochemistry was performed. On 10 cases, double staining with EMA (HRP) and S100 (Alk Phos) was performed.
Results: 21 patients were female, and 18 male (mean age 38 years; range 2-85; 70% 2nd-5th decades). Most patients presented with a painless nodule. The tumors arose in a wide distribution: 16 lower limb; 12 upper limb; 6 head & neck; 4 trunk; 1 colon. None of the patients showed signs of neurofibromatosis (NF). Tumor size ranged from 0.7-17.5 cm (mean 3 cm). Most tumors involved superficial subcutis (8 also dermis); only 2 were intramuscular. Histologically, the tumors were usually well-circumscribed but unencapsulated, and composed of spindle cells with plump, tapering nuclei and palely eosinophilic cytoplasm with indistinct cell borders, arranged in a storiform, whorled, and/or lamellar architecture. Only one tumor showed infiltrative margins. One tumor showed a plexiform growth pattern. Antoni A and B zonation and hyaline vessels were absent. Six tumors showed focally myxoid stroma, and 10 showed scattered cells with degenerative nuclear atypia. Mitoses ranged from 0-4 per 30 HPF; 29 had no mitoses. All tumors showed staining for S100 and EMA; 97% were positive for CD34, 85% for GFAP, and 78% for claudin-1. Twelve tumors contained rare NFP-positive axons. Double staining for EMA and S100 revealed parallel layers of alternating S100 and EMA-positive cells with no co-expression of antigens by the same cells. Most tumors were composed of 60-70% Schwann cells and 30-40% perineurial cells. After a mean follow-up of 24 months (range: 6-60 months), 1 tumor recurred locally, following incomplete excision.
Conclusions: Benign nerve sheath tumors showing predominantly schwannian cytomorphology and perineurioma-like architecture are composed of an admixture of both cell types. These tumors usually arise in the dermis and subcutis and occur over a wide age range and anatomic distribution. Degenerative nuclear atypia (akin to ancient schwannoma and atypical neurofibroma) is relatively common. Hybrid schwannoma/perineuriomas have no association with NF and rarely recur.
Category: Bone & Soft Tissue

Tuesday, March 10, 2009 9:30 AM

Poster Session III # 6, Tuesday Morning