Low Anterior Resection for Rectal Carcinoma

Patient Selection and Preoperative Assessment

The National Comprehensive Cancer Network recommends low anterior resection (LAR) for tumors in the mid to upper rectum where adequate distal clearance can be achieved while preserving anal sphincter function 1, 2
Preoperative staging with pelvic MRI is essential to define locoregional clinical staging, detect extramural vascular invasion (EMVI), determine T substage, and assess distance to the circumferential resection margin (CRM) 3
Rigid rectoscopy and complete colonoscopy are required to exclude synchronous colonic tumors 3
For lower rectal tumors, abdominoperineal resection (APR) is typically required when the tumor directly involves the anal sphincter or levator muscles 1, 2

The primary goal of LAR is to achieve complete tumor removal with adequate margins while preserving sphincter function, with a minimum distal margin of 2 cm standard for adequate tumor clearance 4, 5
At least 6-8 regional lymph nodes should be examined for proper staging 4, 3
LAR extends 4-5 cm below the distal edge of the tumor for mid to upper rectal lesions 1, 2

Patient is placed in modified lithotomy position with Trendelenburg tilt, and access can be via open laparotomy, laparoscopic, or robotic approach 2, 6
Identify and ligate inferior mesenteric vessels at appropriate level, and mobilize the left colon and splenic flexure to ensure tension-free anastomosis 2, 6
Total Mesorectal Excision (TME) involves en bloc removal of the mesorectum with associated vascular and lymphatic structures, with sharp dissection along the mesorectal fascia to preserve autonomic nerves 1, 2, 6
Transect the rectum at least 2 cm distal to the tumor margin, with construction of a colonic pouch to replace the rectal reservoir improving functional outcomes 4, 5
Temporary diverting ileostomy or colostomy may be considered, especially for low anastomoses 2

Ensure complete mesorectal excision with intact mesorectal fascia to minimize local recurrence, and avoid injury to autonomic nerves to preserve urinary and sexual function 4, 3, 1, 2
Circumferential resection margin (CRM) is defined as positive if tumor is within 1 mm from the transected margin 1

Preoperative chemoradiotherapy should be considered for locally advanced rectal cancer (T3/T4 or node-positive) to reduce local recurrence 3, 6
Upper rectal cancers (>12 cm from the anal verge) above the peritoneal reflection should be treated as colon cancer 3

Quality assessment of the TME specimen is essential, including photographic documentation, and pathological examination should include assessment of proximal, distal, and circumferential margins in millimeters 3