What are the steps and principles of low anterior resection (LAR) surgery for carcinoma of the rectum?

Low Anterior Resection for Rectal Carcinoma: Steps and Principles

Low anterior resection (LAR) with total mesorectal excision (TME) is the standard surgical procedure for mid to upper rectal cancers, providing optimal oncological outcomes while preserving sphincter function. 1, 2

Patient Selection and Preoperative Assessment

• LAR is indicated for tumors in the mid to upper rectum where adequate distal clearance (4-5 cm below tumor edge) 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) 1
• Rigid rectoscopy and complete colonoscopy are required to exclude synchronous colonic tumors 1
• For lower rectal tumors, abdominoperineal resection (APR) is typically required when the tumor directly involves the anal sphincter or levator muscles 1, 2

Principles of Low Anterior Resection

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

Surgical Steps of Low Anterior Resection

1. Patient Positioning and Access

   • Patient is placed in modified lithotomy position with Trendelenburg tilt 2
   • Access can be via open laparotomy, laparoscopic, or robotic approach 1, 2

2. Vascular Control and Mobilization

   • Identify and ligate inferior mesenteric vessels at appropriate level 2
   • Mobilize the left colon and splenic flexure to ensure tension-free anastomosis 4

3. Total Mesorectal Excision (TME)

   • TME involves en bloc removal of the mesorectum with associated vascular and lymphatic structures 1, 2
   • Sharp dissection along the mesorectal fascia ("holy plane") to preserve autonomic nerves 1
   • Complete excision of the mesorectum for tumors of the lower and middle third of the rectum 1

4. Rectal Transection

   • Transect the rectum at least 2 cm distal to the tumor margin 1, 3
   • For mid-rectal tumors, transection typically occurs 4-5 cm below the distal tumor edge 1, 2

5. Anastomosis Creation

   • Colorectal or coloanal anastomosis can be performed using stapling devices or hand-sewn techniques 5, 4
   • Construction of a colonic pouch to replace the rectal reservoir improves functional outcomes 1
   • Ensure tension-free anastomosis with good blood supply 4

6. Diverting Stoma Consideration

   • Temporary diverting ileostomy or colostomy may be considered, especially for low anastomoses 5, 4

Technical Considerations and Pitfalls

• Ensure complete mesorectal excision with intact mesorectal fascia to minimize local recurrence 1
• Avoid injury to autonomic nerves to preserve urinary and sexual function 1, 2
• Circumferential resection margin (CRM) is defined as positive if tumor is within 1 mm from the transected margin 1
• Anastomotic leak rates can be high (up to 48% in very low anastomoses), necessitating careful technique and consideration of diverting stoma 5

Special Considerations

• For tumors in the lower third of the rectum, intersphincteric resection may be an option to avoid APR in selected patients 5
• Preoperative chemoradiotherapy should be considered for locally advanced rectal cancer (T3/T4 or node-positive) to reduce local recurrence 1
• Upper rectal cancers (>12 cm from the anal verge) above the peritoneal reflection should be treated as colon cancer 1

Postoperative Considerations

• Quality assessment of the TME specimen is essential, including photographic documentation 1
• Pathological examination should include assessment of proximal, distal, and circumferential margins in millimeters 1
• Functional outcomes may include altered bowel habits, urgency, and decreased resting anal pressure 5

LAR with TME provides good oncological outcomes with 5-year disease-free survival rates of 78-83% and local recurrence rates as low as 7% when performed with appropriate technique 6.