Dissecting Leiomyomas of the Uterus Other Than Cotyledonoid Dissecting Leiomyomas

We report eight cases of benign uterine smooth muscle neoplasms with unusual growth patterns and intramural dissection. All the patients in our series were of reproductive age or perimenopausal (range, 36-51 years) and had an enlarged uterus or a pelvic mass, with the exception of one lesion that was found incidentally in a patient treated for uterine prolapse. Three also had abnormal uterine bleeding. On gross examination, the lesions had an unusual appearance and were often lobulated and irregular with indistinct margins. On microscopic examination of all the lesions in this study, a dominant benign smooth muscle tumor was associated with intramural dissection of the myometrium by fascicles of neoplastic smooth muscle. Of the eight cases showing intramural dissection, four were intramural dissecting leiomyomas; three were examples of intravenous leiomyomatosis; and one was a multinodular leiomyoma with hydropic degeneration. We excluded cotyledonoid dissecting leiomyomas from the study. In two of the three cases of intravenous leiomyomatosis, extrauterine extensions in continuity with the intramural components were noted at surgery and on gross examination. Intramural dissection of the myometrium by a benign smooth muscle tumor is one additional possibility to be considered in the differential diagnosis of leiomyosarcoma and low-grade stromal sarcoma.