Expect the unexpected: Endometriosis mimicking a rectal carcinoma in a post-menopausal lady

A 50-year-old post-menopausal lady presented with complaints of pain in the left lower abdomen since 1-year. She had altered bowel habits and mucus in stools but no blood in it with a history of anorexia and unquantified weight loss. Clinical examination was non-contributory. A computed tomography (CT) scan picked up a 4.5 cm × 3 cm × 4.5 cm enhancing mass in the rectosigmoid region. The fat planes between the mass and the left ovary/uterus were lost [Figure 1a and b ]. A colonoscopy found a polypoidal mass at 18 cm with intact mucosa [ Figure 1c ]. A biopsy from it on two occasions did not reveal a malignancy. Thereafter, an ultrasound-guided fine-needle aspiration cytology (FNAC) was done which too was inconclusive. The carcinoembryonic antigen was 4.7 ng/ml. (a and b) Axial and coronal section of computed tomography scan showing the growth in rectosigmoid with loss of planes with uterus and ovary. (c) Endoscopic view showing the mass. (M: Mass, U: Uterus, O: Ovary) With a presumptive diagnosis of a rectal gastrointestinal tumor (GIST), the patient was taken up for surgery with a tentative plan of laparoscopic anterior resection and an en bloc resection. Per op, a growth was seen at the rectosigmoid which had infiltrated the left ovary [ Figure 2a ]. The uterus was uninvolved. She underwent a laparoscopic anterior resection with an en bloc left oophorectomy with double-stapled colorectal anastomosis [ Figure 2b ] and a covering loop ileostomy. The post-operative recovery was uneventful. The histopathology reported foci of endometrial glands and stroma in the bowel, ovary and adjoining lymph nodes, consistent with endometriosis [Figure 2c and d ]. She has completed 6 months follow-up and is doing well. Her bowel continuity has been restored. (a) Laparoscopic view showing the mass infiltrating the ovary. (b) The rectum being divided at the level of peritoneal reflection in preparation for a double stapled colorectal anastomosis. (c) Photomicrograph showing benign endometrial glands and stroma embedded in muscularis propria of the rectosigmoid (H and E, ×100). (d) Photomicrograph showing Endometriosis in lymph node (H and E, ×40)

When an elderly patient presents with a rectal mass along with and altered bowel habit, the diagnosis seems straightforward, a rectal cancer. However, at times, the ultimate diagnosis could turn out to be different. Endometriosis affecting the bowel is known, and the most common segment of involvement is the rectum and sigmoid colon.[ 1 ] However, endometriosis is rare in a post-menopausal lady.[ 2 ] We report an unusual case of a post-menopausal lady, with no past history of endometriosis or hormone replacement therapy (HRT), who had a rectal endometriosis that mimicked a rectal carcinoma.

In a patient of reproductive age group presenting with a rectal mass and an attempted biopsy is inconclusive for malignancy, we should consider a diagnosis of endometriosis. In ­post-menopausal patients, though rare, it may still be worthwhile to entertain this diagnosis.

Endometriosis is defined as the presence of functional endometrial tissue outside the uterine cavity. It is an estrogen-dependent disease and thus occurs exclusively in fertile women.[ 2 ] When seen in post-menopausal women, it is usually associated with HRT.[ 3 ] Their occurrence is rare in post-menopausal women not on HRT. The prevalence of endometriosis is only 6-10% and of all these cases, only 2-5% are post-menopausal women.[ 4 ] The etiopathogenesis of endometriosis in post-menopausal women is attributed to the coelomic metaplasia theory. Another plausible explanation for this occurrence is the endometrial stem cells from vascular endometrial cell transportation which can occur when the endometriosis appears in sites that would not have come in contact with the retrograde menstrual flow.[ 5 ] Endometriosis often involves the ovary and the pelvic peritoneum, but in 9-12% it could involve extragonadal sites. When it involves the intestine, the most common site of involvement is the sigmoid colon and rectum (85%), followed by distal ileum (7%). Caecum (3.6%) and the appendix (3%) are involved the least.[ 1 ] Our patient is the rare post-menopausal lady with no HRT who developed an extragonadal endometriosis involving the rectosigmoid. The presentation of intestinal endometriosis depends on the segment of bowel involved. In the most common rectosigmoid variety, they usually present with altered bowel habits and pain. Rectal bleeding can occur when the endometriosis penetrates to the mucosa or when severe colonic fibrosis results in ischemia. All these could very well be features of malignancy too, as was the case in our patient. Colonic endometriosis may present as an emergency with perforation peritonitis. Small bowel involvement may present as intestinal obstruction or vague abdominal pain and bloating.[ 6 ] Radiological and endoscopic diagnostics are essential in the investigation of such cases. Most endometriosis involving intestine are superficial deposits and may not involve the mucosa. Colonoscopy will only be able to pick up lesions which involve the mucosa or cause a large enough bulge when the mucosa is uninvolved. A biopsy can be taken if the mucosa is involved, but most yield a report of chronic inflammation and only occasionally is a definitive diagnosis made.[ 6 ] CT scans can pick up the mass lesions, but a magnetic resonance imaging is said to be the most sensitive imaging technique for intestinal endometriosis.[ 7 ] It is important to understand that these evaluations may not clinch a definitive diagnosis and rule out a malignancy conclusively. The gold standard in the management of these cases is diagnostic laparoscopy or laparotomy.[ 6 ] A biopsy can be taken and sent for frozen section. Once a confirmation of endometriosis is received further management will depend on the clinical scenario. Most patients with significant symptoms and involvement of muscularis propria or those with diagnostic dilemma are best managed by surgery. Once the muscularis is involved, the endometriotic tissue in the muscularis undergoes muscle cell hyperplasia and fibrosis, which make it resistant to medical treatment.[ 8 ] The options in a rectosigmoid endometriosis are either an anterior resection or a low anterior resection along with en bloc resection of adjacent pelvic organs depending on the extent and best-accomplished laparoscopically. If the patient is minimally symptomatic, the lesion is superficial and patient desires future pregnancy, then medical management may be offered and response assessed. Medical management could be in the form of danazol, high-dose progestins, or GnRH agonists, all of which have shown equivalent efficacy.[ 9 ] Aromatase inhibitors anastrozole and letrozole have also shown results in this subset of post-menopausal patients.[ 10 ] If a definitive pre-operative diagnosis can be made, then a period of medical therapy before surgery may decrease inflammation and vascularity which may render the surgery easier. The presence of endometriosis in pelvic lymphnodes is uncommon but is more often associated in bowel endometriosis. This may be a result of lymphovascular invasion or a metaplastic process. Our case mimicked a rectal cancer because of similar radiological and colonoscopic findings in the back ground of the clinical presentation combined with the inability of the biopsy/FNAC to clinch a pre-operative diagnosis. With a large submucosal tumor, a strong possibility was a GIST. So we took up the patient for surgery. Even on laparoscopy, it seemed to us as if it were a rectosigmoid growth which had infiltrated the ovary and hence an anterior resection with en bloc left oophorectomy was done. The histopathology took us by surprise.