MRI pelvis as a problem-solving diagnostic tool in clinically and histologically unsuspecting case of rectal wall endometriosis

A 30-year-old woman presented to the gastroenterology department with complaints of constipation, abdominal pain, hematochezia, 4-5 kg weight loss, and vaginal spotting for 5 months. Her rectal examination did not reveal any abnormality. Pelvic examination showed a bulky, hard cervix that was bleeding to the touch and a polypoidal growth in the posterior fornix. Colonoscopy showed an anterior rectal wall lesion with nodular mucosa. A clinical diagnosis of pelvic malignancy was made and biopsies were taken from the rectal wall and vaginal fornix growth which showed non-specific inflammation.

CT abdomen revealed asymmetric anterior rectal wall thickening with mild enhancement, contiguous with the cervix causing obliteration of pouch of Douglas(POD) (Figure 1a). After the administration of positive rectal contrast, polypoidal/frond-like rectal mucosal projections were seen from the anterior rectal wall (Figure 1b). CT suggested the possibility of endometriosis. However, because of the high clinical suspicion of malignancy and non-diagnostic biopsy reports, MRI pelvis with contrast was performed for confirmation.

MRI pelvis revealed poorly circumscribed, spiculated, heterogenous T2 hypointense soft tissue thickening obliterating the POD (yellow arrows in Figure 2a), involving posterior vaginal fornix, showing numerous tiny T1 and T2 hyperintense cystic foci within (Figure 2b, 2c). It is flush with the posterior wall of the cervix and uterocervical junction anteriorly. Posteriorly, there is contiguous hemicircumferential T2 hypointense anterior rectal wall thickening replacing the muscularis propria with intact overlying rectal mucosa which is thrown into numerous folds seen as polypoidal/frond-like mucosal protrusions into the rectal lumen (Figure 3a). Superiorly, the soft tissue thickening is adherent to the left ovary. There were a few associated T1 hyperintense left ovarian cysts with T2 shading (yellow asterisk in Figure 3a). These imaging findings were highly suggestive of deep infiltrating pelvic and rectal wall endometriosis.

Background

Endometriosis is defined as the presence of endometrial glands and/or stroma outside the uterine cavity. Endometriosis is categorized into ovarian endometriosis, superficial endometriosis(also known as peritoneal endometriosis), and deep infiltrating endometriosis(DE). DE is the most severe form of the disease and is histologically defined as endometriosis infiltrating the retroperitoneum or the wall of pelvic organs by at least 5 mm[1]. Bowel involvement accounts for 4-37% of the women presenting with DE; rectum and sigmoid involvement contribute up to 85% of all intestinal lesions[2,3]. Intestinal endometriosis most commonly affects serosa or muscularis propria; mucosa often exhibits non-specific inflammatory infiltration, ulceration, cryptitis, or architectural changes[4].

Clinical Perspective

Intestinal endometriosis patients often present with non-specific symptoms including abdominal/pelvic pain, gastrointestinal bleeding, altered bowel habits, dyschezia, dysmenorrhoea, dyspareunia, and infertility. Symptoms might be cyclical or might not be related to menstruation. Imaging helps in diagnosis and delineating the extent and severity of the disease. In our case, there was strong clinical suspicion of pelvic malignancy and multiple biopsies from the cervix, vaginal fornix and rectal wall showed non-specific inflammatory changes with no features of dysplasia or malignancy.

Imaging Perspective

TVS is the first line of investigation when patients present primarily with gynecologic symptoms which have up to 95% sensitivity and 100% specificity in diagnosing colorectal involvement. It is characterized by hypoechoic linear thickening, nodules, or masses involving the posterior pelvis (uterosacral ligaments, vagina, cervix, and rectosigmoid). Bowel wall involvement is characterized by hypoechoic thickening of muscularis propria with overlying intact hyperechoic submucosa and mucosa[5]. MDCT with rectal enema is not considered the primary imaging modality in diagnosing recto-sigmoid endometriosis due to limitations such as ionizing radiation and the need for intravenous iodinated contrast[6]. CT shows enhancing poorly defined solid lesions causing bowel wall thickening with similar extramural enhancing nodules adjacent to the bowel loop obscuring the intervening planes, suggesting the presence of extrinsic bowel lesions. MR imaging demonstrates good specificity(97.8%) and accuracy(94.9%) in the prediction of rectosigmoid endometriosis[7]. The typical MRI findings of deep pelvic endometriosis involving the rectum depend on the depth of rectal wall involvement, only serosal involvement appears as T2 hypointense thickening in the cul-de-sac abutting anterior rectal wall with loss of fat plane on the serosa and deeper involvement of muscularis propria is characterized by low to intermediate signal intensity wall thickening in a fan-shaped configuration with the mucosa and submucosa appearing bright at the growing edge on T2 sequence(“mushroom cap” sign) and obliteration of perienteric fat planes between uterus and rectum. It can show punctate foci of T1 hyperintensity within the T2 hypointense fibrotic thickening representing regions of hemorrhage[8]. Infiltration of submucosa may be difficult to assess on MRI, as submucosal thickening may be caused by oedema and not necessarily endometrial tissue[9].

Outcome

After multiple non-contributory superficial biopsies which showed non-specific inflammatory cells, MRI pelvis revealed findings highly suggestive of rectal wall endometriosis, further confirmed by endoscopic ultrasound-guided final needle aspiration biospy. Treatment of deep pelvic endometriosis involves a multidisciplinary approach with surgical planning aiming to radically remove all endometriosis lesions. Surgical options include rectal shaving or discoid resection (conservative approach) or segmental bowel resection. The latter is recommended when there is >50% bowel circumference involved (or) when the nodules are larger than 3cm[10]. Long-term hormonal therapy may be considered for patients who are not surgical candidates. In our case patient opted for hormonal therapy before going for surgery.

Take home message. Teaching point

One must have a high index of suspicion of intestinal endometriosis in reproductive age group women when imaging shows the above findings although colonoscopy may show normal or non-specific findings. Pelvic MRI is helpful for a definitive diagnosis like in our case where superficial biopsies were non-contributory.