# Magnetic Resonance Roadmap in Detecting and Staging Endometiosis: Usual and Unusual Localizations
## 3 Localization
### Deep Infiltrating Endometrosis (DIE)  
DIE occurs if the endometrial tissue has penetrated at least 5 mm beyond the surface of the peritoneum. It is the most aggressive form of endometriosis, often associated with a symptomatology that may not benefit from medical therapy alone. DIE is often associated with conditions of infertility. The role of the radiologist and the MRI, in this case, is to provide indications to the surgeon on the location of the lesions and their extension in order to correctly plan surgery.  
Recently, the ENDOVALIRM group has examined the literature and has established an MRI lexicon consensus in the management of DIE [39].  
According to them, the pelvis should be divided into the following nine compartments, with each one containing specific structures:  
- Right and left anterolateral compartments: distal round ligament;  
- Anterocentral: proximal round ligament and bladder;  
- Right and left mediolateral: parametrium, ureter, uterine artery and pelvic wall (external iliac and/or obturator vessels);  
- Mediocentral: torus, proximal uterosacral ligaments, posterior vaginal fornix, rectovaginal septum, anterior mesorectum and external adenomyosis;  
- Right and left posterolateral: distal uterosacral ligaments, sacro-reclal-genital septum and pelvic wall (sacral roots, sciatic nerve, internal iliac vessels);  
\begin{table}
\begin{tabular}{c c c c} \hline  & Localization & MRI Sign & MRI findings \\ \hline Ovary & Ovarian endometrioma & T1 high signal multiplicity & Multiple high signal cyst on T1 WI \\  & & T2 shading & Marked gradation or shading on T2 WI \\  & & T2 dark spot sign & Well-defined markedly hypointense foci \\  & & & within the cyst on T2 WI \\ \hline Deep infiltrating & Posterior & & Hypointense nodular lesions (T1/T2 WI) \\ endometriosis & cul-de-sac-obliteration & & Soft tissue thickening with irregular, \\  & & & indistinct or stellate margins (T1/T2 WI) \\  & & & Elevated posterior vaginal fornix on \\  & & & T1/T2 WI \\  & & & Intestinal / rectum tethering towards \\  & & & uterus on T2 WI \\  & & & Fibrotic plaques or nodules covering the \\  & & & serosal surface of the uterus on T2 WI \\  & & & Retrouterine fibrous mass on T2 WI \\  & & & T2 WI low-intensity thickening or mass \\  & & & with regular/irregular margins \\  & & & Bilateral ovaries located on top of the uterus \\  & & & Thickened and irregular with a \\  & & & nodular appearance \\  & & & Focal thickening of the rectal wall \\  & & & \\  & & & Hypointense nodules on T1/T2 WI \\  & & & Hypointense solid mass on T2 WI \\ \hline Extra pelvic & & & with/Without hyperintense hemorrhagic \\ endometriosis & Abdominal wall & & cyst on T1 WI \\  & & & Hyperintense nodules on T1 WI \\ \hline \end{tabular}
\end{table}
Table 1: The table schematically represents the main localizations of DIE, MRI sign and their appearance in each of the sequences [7,8,14,16].  
Posterocentral: rectum and rectosigmoid junction.  
They also assigned a tenth compartment to extrapelvic lesions (sigmoid colon, cecum, ileum, appendix, extrapelvic ureters, abdominal wall and inguinal regions).  
In our review, we focus on the main structures involved in DIE, specifically on related symptomatology and MRI appearance.