Cutaneous sclerosing perineurioma of the digit.

An 11-year-old Japanese girl noticed a small nodule, with mild tenderness, on the right index finger 5 years before visiting our outpatient clinic. She had no familial history of neurofibromatosis or past history of traumatic injury at the site of the tumor. Physical examination revealed a slightly elevated, subcutaneous, nodular tumor in the volar aspect between the proximal and distal interphalangeal joints of the digit (Fig. 1A). By magnetic resonance imaging examination, the tumor showed low density on both T1- and T2-weighted images, and was located just adjacent to the tendon with no invasive signs. The tumor was extirpated; at operation, it was well circumscribed and mobile without adhesion to adjacent tendon or nerve, and was easily removed. Grossly, the tumor was a well-circumscribed, firm nodule (10 mm x 8 mm x 5 mm in size) (Fig. 1B). The cut surface was whitish, homogeneous, and solid without cystic lesions. Histologically, it was an unencapsulated, paucicellular dense, fibrous nodule with a concentric circular arrangement of collagen bundles (Fig. 2A). Amongst the fibrous bundles, a small number of ovoid/epithelioid or plump spindle cells were arranged in a corded, trabecular, or whorled (onion bulb-like) pattern (Fig. 2B); a storiform pattern was not noted. These cells were relatively uniform and had a somewhat elongated, slightly hyperchromatic nucleus with fine granular chromatin. Neither nuclear pleomorphism nor multinucleated cells were evident, and necrosis and mitotic figures were not observed. Periodic acid-Schiff (PAS) stain after diastase digestion highlighted the corded or whorled pattern of the tumor cells by encasing them. For immunohistochemical examination, formalin-fixed, paraffin-embedded serial tissue sections were stained by a labeled streptavidin-biotin method. The tumor cells were positive for vimentin and epithelial membrane antigen (EMA) (Fig. 3A), and negative for pan-cytokeratin, carcinoembryonic antigen (CEA), CD34, alpha-smooth muscle actin, desmin, and CD68. Type IV collagen and laminin (Fig. 3B) were detected along the cords or whorls of the tumor cells, similar to the staining pattern of the diastase-PAS reaction. Schwann cells and axonal components, immunoreactive for S100 protein and neurofilament, respectively, were focally detected just adjacent to the cords or whorls, although the tumor cells per se did not express these proteins. Consequently, the tumor was found to be perineurial in origin and was diagnosed as cutaneous sclerosing perineurioma.