Soft-tissue perineurioma. Evidence for an abnormality of chromosome 22, criteria for diagnosis, and review of the literature.

Reported herein are two examples of soft-tissue perineurioma (STP), one arising in the maxillary sinus and the other in subcutaneous tissue of the thigh. Electron microscopy and immunohistochemistry were performed in both cases. Based on our findings and a critical review of the literature, STPs are generally small, well-circumscribed but not encapsulated tumors. Histologically, most STPs resemble fibroblastic tumors, being composed of elongated, wavy cells. The immunohistochemical reactivity for epithelial membrane antigen, the lack of reactivity for S-100 protein, and the presence of ultrastructural features of perineurial cells are typical of this tumor. To explore the possibility that STP, like the intraneural variety of perineurioma, exhibits an abnormality of chromosome 22, we performed fluorescence in situ hybridization with a probe specific for the M-bcr locus, which maps to the chromosome band 22q11. In both our tumors, a high percentage of nuclei having only one M-bcr signal (44 and 96%) was observed. Our findings indicated deletion of part or all of chromosome 22 and support the view that both soft-tissue and intraneural perineurioma are part of a spectrum of perineurial neoplasia.