Nerve sheath myxoma (neurothekeoma) arising in the oral cavity: histological and immunohistochemical features of 3 cases.

This report describes the histological and immunohistochemical characteristics of 3 cases of nerve sheath myxoma (NSM)/neurothekeoma arising in the oral cavity. Histopathologically, 3 distinct variants were observed based on the amount of myxoid matrix: classic/hypocellular, cellular, and mixed types. Immunohistochemically, all types expressed strong immunoreactivity to S-100 protein (3/3), NSE (neuron-specific enolase) (3/3), and NGFR (nerve growth factor receptor) (3/3), whereas all cases were negative for SMA (smooth muscle actin) and FVIII. The number of Ki-67 positive cells was less than 5% in all lesions confirming the slow growing characteristics of NSM. The results suggest that NSMs of the oral cavity are true peripheral nerve sheath tumors and show close relationship to schwannoma.