Granular perineurioma: the first report of a rare distinctive subtype of perineurioma.

Perineurioma represents a relatively recently described neoplasm in the spectrum of benign peripheral nerve sheath tumors composed of perineurial cells staining immunohistochemically positive for epithelial membrane antigen. Although intraneural, extraneural and sclerosing perineurioma, rare variants of perineurioma, do occur, and knowledge of them is important in the differential diagnosis of mesenchymal tumors of different lines of differentiation and more importantly if their clinical course differs from that of other perineuriomas. We report herein the first case in the world literature of granular perineurioma arising in the dermal and subcutaneous tissues of the trunk of a 28-year-old female. The diagnosis was confirmed morphologically and immunohistochemically. More interestingly, 3 years later the patient complained of right lower extremity pain, for which magnetic resonance imaging studies showed an intraneural perineurioma confined to the sciatic nerve. The latter finding was confirmed both histopathologically and immunohistochemically to have exactly the same appearances of the original dermal and subcutaneous mass. Neoplastic cells stained positively for epithelial membrane antigen and for the newly described antibodies claudin-1 and glut-1. Interestingly, the granular component of this large tumor (4.5 cm in maximum diameter) was negative for S100, but positive for NKI-C3. The morphology, immunohistochemistry, and the clinical behavior for this tumor and the differential diagnoses are discussed.