Hybrid Schwannoma/Perineurioma

Abstract

Hybrid schwannoma/perineurioma is a recently described benign nerve sheath tumor that typically manifests as a dermal tumor on the extremities and trunk. Occurrence outside the skin is uncommon. This article describes 10 cases of hybrid schwannoma/perineurioma arising in diverse anatomic locations. They all occurred in adult patients (age range 27-81 years, median 35 years) with a marked female predominance (2 males and 8 females). Of the 10 tumors, 7 were situated in the subcutis of trunk (n = 3), extremities (n = 2), neck (n = 1), and labium majus (n = 1) and 3 in the submucosa of nasal cavity, sigmoid colon, and rectum, respectively. Histologically, they were composed of intimately admixed plump spindle cells and elongated slender spindle cells forming storiform, lamellar or fascicular architecture. By immunohistochemistry, the tumor showed dual differentiation of schwannian cells (plump-spindled) and perineurial cells (slender-spindled), characterized by strong S100 protein expression in the former component and variable immunoreactivity of epithelial membrane antigen, claudin-1, and CD34 in the latter. Awareness of its morphological characteristics and potential occurrence in diverse sites may aid in the recognition of this rare tumor type.