Endometrial stromal sarcoma located in the myometrium with a low-intensity rim on T2-weighted images: report of three cases and literature review.

Endometrial stromal sarcoma (ESS) most commonly grows from the uterine endometrium into the endometrial cavity; it is rarely located in the myometrium alone, where it may resemble degenerated leiomyoma on magnetic resonance imaging (MRI). We present three cases of intramyometrial ESS mimicking degenerated leiomyoma, all of which have a characteristic low-intensity rim on T2-weighted images. Histopathological examination revealed the rim to consist of fibrous tissue layers and/or a decrease in free water caused by distortion of myometrial tissue following tumor expansion. ESS should be included in the differential diagnosis of intramyometrial mass with low-intensity rim on T2-weighted image, especially if the mass shows degeneration with no or mild intratumoral hemorrhage.