Abstract
Adenomyoma is a benign tumor composed of endometrial glands, specialized endometrioid stroma, and smooth muscle. These tumors typically originate within the uterus. An extrauterine adenomyoma is an extremely rare entity. We present the case of a 56-year-old perimenopausal woman with a right adnexal mass, diagnosed histopathologically as an ovarian ligament adenomyoma. This report documents a fourth case of an extrauterine adenomyoma and only the second case in ovarian ligament. The differential diagnosis includes endometrioma, leiomyomatosis peritonealis disseminata, uterus-like mass lesion and extrauterine leiomyoma with entrapped endometrioid glands and stroma. Two theories for the etiology of adenomyoma have been proposed: (i) Mullerian duct fusion defect and (ii) metaplasia.