Deep pelvic endometriosis: don’t forget round ligaments. Review of anatomy, clinical characteristics, and MR imaging features Benedetta Gui, Anna Lia Valentini, Valeria Ninivaggi, Marzia Marino, Marta Iacobucci, Lorenzo Bonomo Department of Bioimaging and Radiological Sciences, Catholic University of the Sacred Heart, Agostino Gemelli Hospital, Largo Agostino Gemelli 8, Rome, Italy Abstract Deep infiltrating endometriosis is an important gyneco- logic disease that may develop during the reproductive years and is responsible for severe pelvic pain. Deep pelvic endometriosis can affect the retrocervical region, uterosacral ligament, rectum, rectovaginal septum, va- gina, urinary tract, and other extraperitoneal pelvic sites. Surgery remains the best therapeutic treatment for af- fected patients and an accurate preoperative evaluation of the extension of endometriotic lesions is essential for a successful outcome. However, many atypical locations for deep pelvic endometriosis exist although still lesser known to both gynecologists and radiologists such as endometriosis of the round ligaments of the uterus (RLUs). In this article, we review embryology and anatomy of the RLUs as well clinical characteristics associated with these endometriotic locations. In addi- tion, we describe magnetic resonance (MR) imaging protocol, normal MR imaging appearances of the RLUs and the most common abnormal findings of endometri- otic involvement of these ligaments at MR imaging. Radiologists should always keep in mind the RLUs as a possible site of deep pelvic endometriosis localization and should not forget to carefully look for them on MR images. Key words: Round ligament of the uterus—Deep infiltrating endometriosis—MRI Endometriosis is the presence of functional endometrial glands and stroma outside the uterine cavity and affects approximately 10 to 20% of reproductive—age women [1]. Pain is the cardinal symptom of endometriosis; the patients may have various types of pain such as dys- menorrhea, dyspareunia, pain during defecation, or uri- nating. Menstrual irregularities and infertility are also commonly present. According to Siegelmen et al. [2] there are three forms of pelvic endometriosis: (1) superficial peritoneal lesions; (2) ovarian endometrioma; (3) deep (or solid infiltrating) endometriosis (DIE), which is histologically defined as a lesion that extends more than 5 mm into the subperito- neal space and/or that affects the wall of pelvic organs and ligaments [1, 2]. DIE predominantly affects posterior structures such as uterine torus and uterosacral ligaments (69.2%) and the vagina (14.5%) as well as other sites as alimentary tract (9.9%) and urinary tract (6.4%)[3]. Uterine liga- ments may also be affected by DIE with reported vari- able frequency, between 0.3 and 14%, depending on the authors, for the round ligaments [1, 4, 5]. The standard treatment of DIE is a complete surgical excision of endometriotic implants; presurgical accurate localization of the lesions is extremely important for successful outcomes. The round ligaments of the uterus (RLUs) are an atypical location for endometriosis and the diagnosis is rarely considered pre-operatively. Symptoms are non- specific, and thus disease at this site is overlook resulting in incomplete surgical excision. MR imaging is an excellent method for identifying and mapping multiple deeply infiltrating endometriotic lesions, given its large field of view, multiplanar capa- bility and high contrast resolution without the use of Correspondence to: Benedetta Gui; email: bgui@rm.unicatt.it ª Springer Science+Business Media New York 2014 Abdominal Imaging Abdom Imaging (2014) DOI: 10.1007/s00261-014-0091-3