Fibrofolliculoma with ancient/pseudosarcomatous features.

Fibrofolliculoma is a benign skin lesion that, when multiple, can be part of the Birt-Hogg-Dube syndrome. We report on a case of solitary fibrofolliculoma arisen on the nose of a 63-year-old woman, with peculiar histological and immunohistochemical features. The lesion was characterized by the presence of bizarre multinucleated perifollicular stromal cells, positive for factor XIIIa, in a background of CD34-positive cells, and by a peripheral population of CD34-positive spindle cells organized in fascicles haphazardly infiltrating the deep dermis, and surrounded by scattered factor XIIIa-positive dendrocytes. We consider the bizarre perifollicular cellular component as an 'ancient' feature of fibrofolliculoma, hypothesis corroborated by the co-expression of CD34 and factor XIIIa, whereas the peripheral spindle cell fascicles represent a pseudosarcomatous proliferation of CD34-positive cells, normally surrounding adnexal structures, stimulated by factor XIIIa-positive dendrocytes.