Neurotecoma celular. Presentación de dos casos Cellular neurothekeoma. Report of two cases

SUMMARY Cellular neurothekeoma is a rare benign cutaneous neoplasm of uncertain histogenesis arising usually on the upper body of children and young adults, with a female predominance. Neurothekeomas (myxoid, cellular and mixed variants) are classically regarded as forming part of a spectrum of tumors of putative nerve sheath origin. The lack of convincing evidence of neurosustentacular differentiation in cellular and mixed variants, however, has challenged this concept, and numerous authors state that they are different tumors that warrant a separate classification. This is the report of two cases of cellular neurothekeoma, in a 24-yearold man and a 9-year-old girl, with asymptomatic tumors occurring on the right shoulder and left knee respectively. Histologically, both cases are characterized by a proliferation of spindle and/or epithelioid cells involving reticular dermis, arranged in fascicles and nests surrounded by sclerotic collagen. One of the two cases show significant cytologic atypia and a notably plexiform pattern. Immunohistochemically, both cases are positive for vimentin, CD68, CD10, factor XIIIa and smoth muscle actin. In one of the two cases there is also immunoreactivity for neuron-specific enolase. The remainder of immunomarkers are negative, S-100 protein included. The immunohistochemical findings suggest fibrohistiocytic differentiation, so it probably warrants the separation of cellular neurothekeoma from myxoid neurothekeoma. In respect to the mixed neurothekeoma, this probably represents a myxoid variant of cellular neurothekeoma.