# Magnetic Resonance Roadmap in Detecting and Staging Endometiosis: Usual and Unusual Localizations
## 3 Localization
### Deep Infiltrating Endometrosis (DIE)
#### 3.2.5 Rectosigmoid Colon  
The presence of endometriosis nodules in the context of the rectal wall generally causes pain (dyspareunia and chronic pain localized posteriorly), dyskinesia and protorragia, the  
Figure 4: Retrocerical endometriosis plaque, intestinal localization, kissing ovaries with bilateral ovarian endometriosis. **(A,B)** Axial T2 WI; **(C)** Coronal T2 WI. Hypointense retrocerical plaque (white arrowhead in **(A)**) localized in the uterine torus with involvement of the utero-sacral ligaments. Adhesions involve both ovaries with bilateral endometriosis (white arrows), which are prolapsed in a retro-uterine position and adhered to the utero-sacral ligaments and the recto-sigmoid junction. There is also an eccentric anterior parietal thickening in the recto-sigmoid junction suggestive of intestinal endometriosis lesion (white dotted arrow in **(A)**).  
Figure 3: Right uterosacral ligament localization in a 43-year-old female. The right uterosacral ligament appears thickened at uterine insertion (white arrow).  
intensity of which depends on the degree of infiltration. Sometimes, rectal endometriosis is associated with an extensive involvement of the recto-vaginal septum with fibrosis that fills the Douglas pouch [41].  
In more than half the cases, rectal lesions are associated with a second intestinal localization.  
The rectum and rectum-sigmoid junction are the most involved sites due to their intraperitoneal position and proximity to the uterus and ovaries [35]. Other intestinal localizations will be described in the following paragraph on atypical localizations.  
On an MRI, lesions appear as irregular thickness or nodules within the intestinal serosa or muscularis propria, hypointense at T2 WI. They rarely affect the submuc or the mucosa, and if infiltrated, we can observe edema and swelling in the area [7] (Figures 5 and 6).  
Figure 5: External adenomyosis and intestinal endometriosis localization in 49-year-old female with story of multiple laparoscopy surgery. Sagittal T2 WI shows a hypointense ill-defined subserosal mass in the posterior myometrium with hyperintense foci (long white arrow), suggestive for external adenomyosis, that cause retracting phenomena towards the anterior wall of the rectum. Additionally, there is deep endometriosis of the posterior compartment with hypointense nodule involving the serous and muscular layers of the anterior wall of the rectum (short white arrow).  
Figure 6: Retrocervical localization, intestinal mushroom cap sign and isthmocele in a 40-years old female. Retrocervical endometriosis localization (white dotted arrow), intestinal “mushroom cap sign” (white arrows) and isthmocele (black arrow).  
What is also important for the radiologist to report, besides the depth and length of the plaques, is the distance between the lesion and the anal margin, as this can affect the type of surgery to be conducted [46]. In severe cases, the MRI shows a circular involvement resulting in a clinical condition of occlusive or sub-occlusive stenosis [47].