Formation of Nerve Twig‐like Nests and Schwannoma in an Unusual Case of Neurofibroma

A case of unusual neurofibroma in an 18-year-old Japanese male is reported. The histology of the tumor was characterized by nerve twig-like nests intermingled with fascicular bundles. In the central portion, the tumor also contained a lobular lesion showing features characteristic of schwannoma. Immunohistochemically, the tumor cells in both the nests and the lobular lesion demonstrated a mostly positive reaction for S-100 protein. S-100 protein-positive and -negative cells were observed in equal numbers in the fascicular bundles surrounding the nests. This unusual nerve sheath tumor in which the S-100 protein-positive cells form both nerve twig-like nests and lobular schwannoma has not been reported previously. The origin of the S-100 protein-positive cells in the two lesions is also discussed.