Neurothekeoma of Gallager and Helwig (dermal nerve sheath myxoma variant): report of a case with electron microscopic and immunohistochemical studies.

A patient presented with a frontal nodule of the scalp. Histopathological examination revealed a myxomatous multilobulate tumor composed of epithelioid cells with variable pleomorphism. Perineurium-like structures were seen but only around isolated lobules located at the tumor periphery. Electron microscopy revealed polygonal cells and cells with elongated cytoplasmic processes. Many cells had myelinoid figures. A basement membrane-like lamina was noted around some cells. Some of the tumor cells were immunoreactive for myelin basic protein. This finding suggests that the tumor cells are of schwannian type. Neurothekeoma of Gallager and Helwig is a rare, probably benign tumor with fairly distinctive histopathologic characteristics. It appears to be a variant of dermal nerve-sheath myxoma.