Hybrid granular cell tumor/perineurioma.

Hybrid peripheral nerve sheath tumors (PNSTs), which show hybrid features of more than one cell type normally found in a peripheral nerve sheath, are recently recognized clinical entities. Various composite tumors have been reported; however, granular cell tumor/perineurioma is a rare combination [1-4]. Since perineurial cells may be found in other types of PNSTs, it is important to determine if those are reactive, remnantal, or true neoplastic when a perineurial component of the PNST is identified. Main differential diagnoses include granular perineurioma and granular cell tumor with reactive perineurial cell hyperplasia, which show a lack of immunopositivity for S-100 in the granular cells and prominent perineurial cell proliferation throughout the tumor, respectively.