This case highlights severe endometriosis and its overlapping appearance with pelvic or rectal malignancy. The degree of thickening of the anterior rectum is particularly noteworthy on CT and could be mistaken for rectal adenocarcinoma.

Endometriosis is defined as endometrial tissue outside the uterus and can impact the ovary, pelvic ligaments, rectosigmoid colon, bladder, cul-de-sac, or surgical scars. It can manifest as superficial/non-invasive implants, ovarian endometrioma or deep/infiltrating which is defined by > 5mm subperitoneal invasion. It can present as pain, dysmenorrhea, dyspareunia, or with infertility.

The presence of T1 hyperintensity in the endometrioma and few smaller foci indicates the presence of blood products. In contrast, deep endometriosis is characterized by fibromuscular hyperplasia¹. Thus, the larger, infiltrative component involving rectovaginal septum is characterized by dark (hypointense) signal on T2, indicating smooth muscle and fibrous proliferation with relative lack of blood products.