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.