[Cotyledonoid dissecting leiomyoma of the uterus. A malignant-looking benign tumor].

The cotyledonoid dissecting leiomyoma of the uterus, or Stenberg tumor, is a rare variant of a smooth muscle benign tumor, classified in the group presenting an unusual growth pattern; clinically, it affects women in reproductive age. We report the case of a 43 year-old woman, who turned up at the Centro Estatal de Atencion Oncologica (State Cancer Care Center) in Morelia, Michoacan, presenting abnormal uterine bleeding and uterine fibroid of major elements. When performing a palpatory bimanual exam, a loose uterus of approximately 7 by 6 inches was identified; it ached when moving. The laboratory tests reported normal parametriums; the ultrasound showed, however, uterine fibroids of major elements. The uterus was enlarged due to a tumor of exophytic growth, which resembles placental cotyledons extended over the uterine surface, composed by smooth muscle nodules that dissected the uterine wall, and with infiltrative appearance in parametriums and the myometrial wall. Despite this microscopic aggressive appearance, a number of ultrastructuctural studies and immunohistochemical techniques proved its benign nature. This can help patients who want to preserve fertility avoid radical surgery.