V4 - Beyond Malignancy: A Multidisciplinary Surgical Approach to Rectal Endometriosis

CME Eligible

Purpose/Background: Endometriosis is a chronic gynecologic inflammatory condition that typically causes chronic pelvic pain. Bowel endometriosis affects 37% of patients with deep infiltrating endometriosis and most commonly involves the rectum and sigmoid colon. Typical symptoms include dyschezia, changes in bowel habits and, in severe cases, bowel obstruction and infertility. Surgical intervention is indicated in symptomatic patients who are refractory to medical management or with evidence of bowel stenosis. Surgical techniques include bowel shaving for superficial lesions with minimal muscularis involvement to discoid resection for lesions with muscularis or submucosal involvement. Bowel nodules >3cm and involving >50% of bowel circumference are typically managed with a segmental resection.

Rectal endometriosis poses a diagnostic challenge, as its clinical presentation and imaging characteristics can closely mimic colorectal malignancy. We present a case of a rectal mass initially suspected to represent clinical T4 rectal adenocarcinoma that was ultimately diagnosed as rectal endometriosis following a stepwise diagnostic and therapeutic evaluation with a multidisciplinary approach.

Methods/Interventions: A 43-year-old female presented with worsening pelvic pain and small perianal abscess to an outside hospital and CT abdomen/pelvis was concerning for a 6x2cm upper rectovaginal mass. A follow-up rectal MRI showed a 7cm spiculated tumor in the mid-rectum with extramural extension into the lower uterine segment, concerning for a T4 rectal adenocarcinoma without lymphadenopathy. No metastatic disease was noted. Tumor markers CEA and CA-125 were 1.8 ng/mL and 75.8 U/mL, respectively. After an initial colonoscopy with rectal mass biopsies showed normal colonic mucosa, the patient was referred for a second opinion and underwent repeat flexible sigmoidoscopy with endoscopic ultrasound-guided transrectal biopsy and final pathology revealed endometriosis.

The patient was referred to Gynecology for further evaluation and underwent a robotic-assisted partial proctectomy with stapled end-to-end anastomosis, total laparoscopic hysterectomy, right oophorectomy, and systematic endometriosis excision.

Results/Outcomes: Pathology resulted in transmural endometriosis of the rectum with free margins.

Conclusion/Discussion: Rectal masses have a wide differential; here, it was misdiagnosed as a malignant tumor given the initial clinical manifestations, imaging, endoscopic findings and nondiagnostic pathological examination. Further biopsies under endoscopic ultrasound ultimately confirmed the diagnosis of endometriosis and ensured appropriate preoperative planning. This case highlights the importance of confirming the diagnosis of rectal masses to ensure a standard treatment approach is followed.