Müllerian adenosarcoma arising from rectal endometriosis.

A Müllerian adenosarcoma is an extremely rare tumor characterized by a stromal component of usually low-grade malignancy and by a benign glandular epithelial component. A Müllerian adenosarcoma occurs mainly in the uterus, but also in extrauterine locations. Extrauterine Müllerian adenosarcomas are thought to arise from endometriotic deposits. A 36-year-old female presented to Daegu Catholic University Medical Center with a symptom of loose stool for several months. The imaging studies revealed a rectal mass, so she underwent a laparoscopic low anterior resection. Although extemporary pathology revealed an inflammatory myofibroblastic tumor, the final histologic diagnosis was a Müllerian adenosarcoma arising from rectal endometriosis. To our knowledge, except a concomitant rectal villotubular adenoma, cases of Müllerian adenosarcomas arising the rectal wall are rare. An adenosarcoma arising from endometriosis should be considered in the differential diagnosis of a pelvic mass, even one appearing in rectal wall, because ectopic endometrial tissue exists everywhere.