What is Low Anterior Resection
Low anterior resection (LAR) is a sphincter-preserving surgical procedure for rectal cancer in which the diseased portion of the rectum is removed through an abdominal approach, followed by reconstruction with a colorectal or coloanal anastomosis, preserving anal sphincter function. 1, 2, 3
Anatomical Definition and Indications
Low anterior resection is the treatment of choice for tumors located in the mid to upper rectum, typically more than 6 cm from the anal verge. 1, 2, 3 The procedure can also be performed for lower rectal tumors when sphincter preservation is technically feasible without compromising oncologic margins. 3
The key anatomical considerations include:
- Tumor location: Must be at least 2 cm above the puborectal muscle on digital examination 4
- Distal margin requirements: At least 2 cm on unfixed specimens for adequate oncologic clearance 3
- Sphincter involvement: The tumor must not directly invade the anal sphincter complex or levator muscles 3
Technical Components
The procedure mandates total mesorectal excision (TME) with sharp dissection along the avascular plane to achieve local recurrence rates below 10%. 1, 3 This requires:
- Intact mesorectal fascia preservation 3
- Examination of at least 12 lymph nodes for proper staging 1, 3
- Circumferential resection margin greater than 1 mm from the mesorectal fascia 3
- For upper rectal tumors, a 5 cm mesorectal margin distal to the tumor 3
Reconstruction Options
After resection, bowel continuity is restored through:
- Colorectal anastomosis: For mid-rectal tumors with adequate distal rectum remaining 1
- Coloanal anastomosis: For lower rectal tumors requiring resection closer to the anal sphincter 1, 2
- Temporary diverting ileostomy: Frequently created to protect the anastomosis, particularly in high-risk cases, though this significantly impacts quality of life until closure 5, 6
Perioperative Management
Mechanical bowel preparation should not be used routinely, except when a diverting ileostomy is planned. 5 When TME with diverting stoma is performed, mechanical bowel preparation may be necessary, though evidence is limited. 5
For locally advanced disease (T3/T4 or node-positive), preoperative chemoradiotherapy (50.4 Gy with 5-FU) is preferred over postoperative treatment, with surgery performed 6-8 weeks after completion. 1, 3
Postoperative Considerations
Pelvic drains should not be used routinely after low anterior resection. 5 Transurethral catheters can be safely removed on postoperative day 1, even with epidural analgesia. 5, 1
Patients require surveillance colonoscopy at 1 year after surgery, then at 3-year intervals. 5 For patients who did not undergo total mesorectal excision or had transanal local excision, additional local surveillance with flexible sigmoidoscopy or endoscopic ultrasound every 3-6 months for the first 2-3 years is recommended due to higher local recurrence risk. 5
Common Complications
Low anterior resection syndrome (LARS) is a highly prevalent complication characterized by incontinence, frequency, urgency, and feelings of incomplete emptying that significantly impacts quality of life. 7, 8, 9 This results from an interplay between mechanical sphincter damage and neural pathway disruption. 9 Treatment includes transanal irrigation, pelvic floor rehabilitation, and biofeedback, with definitive stoma considered only for therapy-refractory LARS persisting beyond 2 years. 9
Critical Distinction from Abdominoperineal Resection
Low anterior resection differs fundamentally from abdominoperineal resection (APR) in that LAR preserves the anal sphincter and avoids a permanent colostomy. 3 APR should be reserved exclusively for very low tumors that directly involve the anal sphincter complex where sphincter preservation is technically impossible. 3