Cutaneous intraneural perineurioma: a case report.

Perineuriomas are benign neoplasms composed of perineurial cells. Classically, perineuriomas are divided into 2 distinct clinicopathologic entities, known as intraneural and extraneural perineuriomas. Intraneural perineuriomas, first described as interstitial hypertrophic neuritis, involve the major nerve trunks, causing motor or sensory deficits. Here, we report a case of a 42-year-old man presenting a lesion on the second finger of the right hand. The patient did not refer any previous trauma, tenderness, or sensorial nerve deficit. Histologic analysis showed a plexiform dermal lesion composed of enlarged nerve fascicles due to proliferation of spindle perineurial cells, arranged in onion-bulb-like structures. The proliferating cells showed positive membranous staining for epithelial membrane antigen and were negative for S100 protein, which highlighted residual Schwann cells. Fluorescence in situ hybridization studies revealed the loss of one signal for chromosome 22 probe in 15% of the spindle cells. In our report, we present the first case of cutaneous intraneural perineurioma, a benign tumor, which expands the morphological spectrum of cutaneous neural lesions.