Shining light in a dark landscape: MRI evaluation of unusual localization of endometriosis

Endometriosis is a disease distinguished by the presence of endometrial tissue outside the uterine cavity with intralesional recurrent bleeding and resulting fibrosis. The most common locations for endometriosis are the ovaries, pelvic peritoneum, uterosacral ligaments, and torus uterinus. Typical symptoms are secondary dysmenorrhea and cyclic or chronic pelvic pain. Unusual sites of endometriosis may be associated with specific symptoms depending on the localization. Atypical pelvic endometriosis localizations can occur in the cervix, vagina, round ligaments, ureter, and nerves. Moreover, rare extrapelvic endometriosis implants can be localized in the upper abdomen, subphrenic fold, or in the abdominal wall. Magnetic resonance imaging (MRI) represents a problem-solving tool among other imaging modalities. MRI is an advantageous technique, because of its multiplanarity, high contrast resolution, and lack of ionizing radiation. Our purpose is to remind the radiologists the possibility of atypical pelvic and extrapelvic endometriosis localizations and to illustrate the specific MRI findings. Endometriotic tissue with hemorrhagic content can be distinguished from adherences and fibrosis on MRI imaging. Radiologists should keep in mind these atypical localizations in patients with suspected endometriosis, in order to achieve the diagnosis and to help the clinicians in planning a correct and complete treatment strategy.