MR imaging of malignancies arising in endometriomas and extraovarian endometriosis

Cancers that arise in ovarian or extraovarian endometriosis are a distinct disease category with a histologic profile different from that of the more common epithelial ovarian cancers and with a better prognosis. Because the malignant transformation of endometriomas is rarely associated with lymphadenopathy or peritoneal carcinomatosis, a high index of suspicion on the part of the radiologist is necessary to establish a timely diagnosis of endometriosis-related ovarian cancers and allow appropriate oncologic management. Although imaging is not currently performed for surveillance of endometriosis, magnetic resonance (MR) imaging is often performed when surgical treatment is under consideration. An optimal MR imaging protocol for the detection of cancer arising in an endometrioma includes a review of subtraction images derived from unenhanced and contrast material-enhanced T1-weighted datasets. Subtraction images provide improved conspicuity of enhancing mural nodules--which are the most sensitive MR imaging sign of malignancy in ovarian endometriosis--against the background of the high-signal-intensity endometriotic cyst. Cancers arising in extraovarian endometriosis typically manifest as solid lesions with intermediate signal intensity on T1- and T2-weighted images, enhancement after the intravenous administration of a gadolinium-based contrast material, and restricted diffusion on diffusion-weighted images and apparent diffusion coefficient (ADC) maps. The signal intensity of myometrium, or, if the uterus is absent, that of the small bowel wall, is used as an internal reference standard for lesion signal intensity. Lesions are considered to have restricted diffusion if they show signal hyperintensity relative to the reference structure on diffusion-weighted images and hypointensity or isointensity relative to that structure on ADC maps. For definitive diagnosis, histopathologic analysis is required.