Abstract

Perineurioma is a rare benign peripheral nerve sheath tumor which stains positive for EMA but negative for S-100 and neurofilament. Mostly located within the subcutis or deep soft tissue, with few tumors arising primarily in the dermis. Despite the reports in the literature, perineurioma remains a little-known tumor. Further, the variability in the morphologic patterns inherent in these tumors, not infrequently leads to diagnostic pitfalls. Herein, we describe seven unusual cases perineuriomas with a comprehensive description of the diverse morphological, immunohistochemical and molecular features.

Institutional review identified 7 unusual cases of perineurioma diagnosed in 2022. Cohort information, including clinicopathologic features, immunohistochemical and molecular features were recorded. Median age was 44 years (16-66) with four males and three females. All showed banal spindled proliferation with good circumscription. Most were positive for EMA/CD34 +/-SMA and negative for S-100 and Desmin. One case was misdiagnosed as DFSP, triggering wide excision and another case of intraneural perineurioma as traumatic neuroma. Molecular analyses available on 2 cases (Case 1 negative for sarcoma gene fusion panel with no NTRK1, NTRK2 or NTRK3 gene fusions and case 3 with mutations in PRGFB).

Tumors showed a spectrum between sclerosing and the ‘usual’ perineurioma with most (85.7%) showing positivity for EMA. Careful attention to the histomorphology will avoid unnecessary tests and catastrophic diagnostic pitfalls.