Teaching Case

A 52-year-old asymptomatic female patient with no significant past medical history presented for a routine colonoscopy screening. During the colonoscopy a submucosal lesion was detected on the anterior wall of the middle rectum. No biopsy was done at the time and an MRI was requested for further investigation.

MRI depicts a 3 cm submucosal lesion on the anterior wall of the rectum, located 8.5 cm from the anal verge. The lesion has circumscribed smooth margins with intermediate signal intensity on T1-weighted images (Fig. 1), low-signal on T2-weighted images (Fig. 2a, 2b) and low-signal intensity on diffusion weighted imaging with high b-value (Fig. 3). Intravenous gadolinium post contrast study revealed no contrast uptake (Fig. 5). An endoscopic ultrasound-guided fine needle aspiration biopsy was suggested (Fig. 6). There was also a small nodular focus, deep on the recto-uterine pouch, of high signal intensity on T1-weighted fat-saturated images (Fig. 4).

Submucosal rectal tumours are frequently asymptomatic lesions discovered incidentally. There are numerous benign and malignant tumours that can present as submucosal rectal lesions, such as leiomyoma, gastrointestinal stromal tumour, primary lymphoma and melanoma [1]. Non-tumoral lesions like endometriosis can also present as a submucosal lesion and congenital cystic lesions, such as the tailgut cyst and duplication cysts, must also be considered as a differential diagnosis [2, 3]. An important differential diagnosis is the presence of an extra-intestinal mass directly invading the rectum, including gynaecologic malignancies [1].

Endometriosis is a condition in which endometrial tissue is found outside the uterus. Most commonly affects the ovaries, but it can affect any organ of the pelvic peritoneum and even infiltrate gastrointestinal tract, urinary tract or spread to extra-abdominal locations [4].
Patients can be asymptomatic or present with chronic pelvic pain and/or infertility or even with unusual symptoms such as cyclic rectal bleeding, haematuria or haemoptysis depending on which organs are affected.
Although laparoscopy or surgery and histological verification are the gold standard for diagnosis, imaging still plays a major role, particularly MR imaging which is highly accurate in the detection of endometriotic cysts, implants and adhesions [4].

Our patient presented with an asymptomatic incidental finding on colonoscopy screening. There were no clinical clues for the diagnosis. Biopsy was initially avoided before imaging studies to avoid biopsy of vascular lesions, which could cause haemorrhagic complications, or extra-intestinal lesions which can directly invade the rectum wall.

Most typical imaging findings of endometriosis are those of lesions that contain blood products and therefore present with high signal intensity on T1-Weighted fat-saturated imaging. These lesions can present as ovarian masses, adhesions or endometriotic deposits on any pelvic organ. The gastrointestinal tract is affected on 12-37% of women with endometriosis [4].

Our patient had no previous diagnosis of endometriosis and presented with a submucosal tumour with intermediate signal on T1 and low-signal on T2. When considering the differential diagnosis of submucosal tumours we focused mainly on leiomyoma, endometriosis and primary lymphoma, since all these lesions can show similar signal intensity characteristics and low contrast uptake, although both lymphoma and leiomyoma usually have higher T2 signal intensity.
A small focus, deep on the recto-uterine pouch, of high signal intensity on T1-weighted fat-saturated images was suspected of being an endometriotic depositum on the rectovaginal septum.
Endoscopic ultrasound-guided fine needle aspiration biopsy showed endometrial cells confirming the diagnosis of endometriotic submucosal rectal implant.