Studies on the cellular origin of neurothekeoma: clinical, light microscopic, immunohistochemical, and ultrastructural observations.

The clinical, histopathologic, and immunohistochemical features of 11 cases of neurothekeoma are reported. One case was examined by electron microscopy. The mean age of the patients was 27.1 years; the study comprised eight female and three male patients. Most lesions were nondescript papules and located on the upper part of the body, seven cases of neurothekeoma on the head. Eight cases were classified as cellular neurothekeoma on the basis of a striking fascicular pattern and three cases as myxomatous neurothekeoma because of prominent myxoid stromal change. All cellular neurothekeomas failed to express S-100 protein, whereas the three myxomatous types were strongly positive for this marker. Other than vimentin, there was no significant immunoreactivity with other immunohistochemical markers. Ultrastructural study of one case of cellular neurothekeoma was inconclusive for cell type although a perineurial origin could not be excluded. On the basis of these results, we conclude that cellular neurothekeoma differs from myxomatous neurothekeoma not only by clinical and histologic findings but also by immunoreactivity with S-100 protein. These findings also suggest the existence of two distinct subtypes of neurothekeoma and possible origin of the two variants of neurothekeoma from different cell types or at least variation in phenotypic expression of a common cell type. On the other hand, it cannot be excluded that these two variants are different stages in the natural history of neurothekeoma.