Cutaneous perineurioma: a poorly recognized tumour often misdiagnosed as epithelioid histiocytoma

Aims Eleven cases of cutaneous perineurioma were studied to further characterize the histological features of this entity. Methods and results The histological and immunocytochemical features of 11 cases of cutaneous perineurioma were studied and detailed by two pathologists. Clinical data were obtained from the referring clinician. Seven patients were female and four were male with ages ranging from 19 to 67 years (median 41 years). Six lesions arose on the leg. Macroscopically lesions ranged from 4 mm to 14 mm in maximum diameter (median 7 mm). Diagnostic histological features included a nonencapsulated but sharply demarcated tumour with a dumbbell architecture. The tumour cells were spindle‐shaped with delicate inconspicuous cytoplasm and arranged in sheets, whorls or with a vague fascicular pattern. Epithelioid cells with moderate amounts of eosinophilic cytoplasm were frequently admixed with the spindle cells. One tumour had trabeculae of cells embedded within a dense collagenous stroma as described in sclerosing perineurioma. One case displayed a prominent myxoid stroma. Three further cases contained small foci of fibrosis or myxoid change suggesting a morphological spectrum exists in cutaneous perineurioma. Mitoses were exceptionally rare and necrosis and significant cytonuclear pleomorphism was not found. All tumours were epithelial membrane antigen (EMA) positive. Six cases showed focal positivity for factor XIIIa. Follow‐up ranged from 5 months to 6 years (median 1 years). No tumour recurred or metastasized. Conclusions The histological appearance of this tumour is broader than hitherto realized. Several cases in this series were misdiagnosed histologically and cutaneous perineuriomas may be more common than currently appreciated.