Testicular (gonadal stromal) fibroma: case report and review of the literature.

A 25-year-old man presented with complaint of a painless enlargement in his left testis. The solid, encapsulated, circumscribed and grayish-white testicular mass displayed the characteristics of testicular fibroma histologically. It was composed of acellular collagenized plaques and hypercellular areas of fibroblastic spindle cells. Immunohistochemically, the neoplastic cells were positive for vimentin and smooth muscle actin, but not for cytokeratin, S-100 protein, desmin, CD99/MIC2 (a protein expressed by Sertoli cells and granulosa cells) and CD34. Only 18 cases of testicular (gonadal stromal) fibroma composed exclusively of spindle cells have been reported to date. An additional case of fibroma, which lacks definite neoplastic sex cord elements, and its differential diagnosis from other mesenchymal lesions of testis are discussed here, together with other cases in the literature.