Perianal mammary-type myofibroblastoma.

We report a unique case of an extramammary mammary-type myofibroblastoma of the perianal region. The patient was a 40-year old female with no significant past history, who presented with a right side painless perianal mass. Gross examination of the excised mass showed a well-circumscribed, apparently encapsulated, nodular mass weighing 30 g and measuring 5 cm. in the greatest dimension. The cut surface showed solid, yellow homogenous tissue. Microscopically, the neoplasm was composed of bland spindled cells generally arranged into short fascicles with abundant myxoid stroma. The cells stained strongly for desmin and CD34. To our knowledge, a review of the literature discloses only ten cases of extramammary, mammary-type myofibroblastoma.