Prenatal magnetic resonance imaging assisting in differentiating between large degenerating intramural leiomyoma and complex adnexal mass during pregnancy.

We present an unusual case in which a 36-year-old patient was referred due to increasing upper left quadrant abdominal pain and a possible left adnexal mass at 22 weeks' gestation. Ultrasonography demonstrated a multiseptated cystic mass, with solid components measuring 12 cm in diameter. A thin sonolucency was thought to separate the mass from the uterus and thus the mass was considered consistent with an adnexal mass, possibly a mucinous cystadenoma. A large degenerating leiomyoma could not be ruled out with certainty and magnetic resonance (MR) imaging was performed which depicted a thin band of myometrium encompassing the complex mass and was therefore diagnostic of a degenerating uterine leiomyoma. We discuss the contribution of MR imaging in the noninvasive diagnosis of undetermined solid pelvic masses visualized ultrasonographically.