Primary Goal of Low Anterior Resection (LAR)
The primary goal of LAR is to achieve complete tumor removal with adequate surgical margins while preserving anal sphincter function, thereby avoiding a permanent colostomy and maintaining quality of life. 1
Oncologic Objectives
The fundamental oncologic goals of LAR include:
- Complete tumor resection with adequate margins - A minimum distal margin of 2 cm is standard for adequate tumor clearance 1
- Total mesorectal excision (TME) - En bloc removal of the mesorectum with associated vascular and lymphatic structures using sharp dissection along the mesorectal fascia 1, 2
- Adequate lymph node harvest - At least 6-8 regional lymph nodes should be examined for proper staging 1
- Negative circumferential resection margin (CRM) - The CRM is considered positive if tumor is within 1 mm from the transected margin 1
Functional Preservation Goals
LAR specifically aims to preserve sphincter function, which distinguishes it from abdominoperineal resection (APR):
- Sphincter preservation - LAR maintains anal sphincter integrity and creates a colorectal or coloanal anastomosis to preserve intestinal continuity 2
- Avoidance of permanent colostomy - This represents a paradigm shift in rectal cancer management, as permanent stomas significantly impact body image, micturition symptoms, and sexual function 3, 2
- Quality of life maintenance - Preservation of anorectal function prevents deteriorations in bowel urgency, frequency, incontinence, and bowel movement clustering that can occur after more radical procedures 3
Patient Selection for LAR
LAR is indicated when specific anatomic criteria are met:
- Tumor location - Mid to upper rectal lesions where LAR extends 4-5 cm below the distal edge of the tumor 1, 2
- Adequate distal clearance - Sufficient distance from the anal sphincter to achieve negative margins while preserving sphincter function 3, 2
- Intact anal function - Baseline sphincter competence must be present 2
When these criteria cannot be met—specifically when the tumor directly involves the anal sphincter or levator muscles—APR with permanent colostomy becomes necessary 3, 2.
Clinical Outcomes Supporting LAR Goals
The evidence demonstrates that LAR successfully achieves its dual goals:
- Oncologic efficacy - Five-year overall survival exceeds 80% with local recurrence rates of approximately 7-10% when proper TME technique is used 4, 5
- Sphincter preservation success - Long-term preservation of anal sphincter function can be achieved in more than 90% of appropriately selected patients 4
- Superior outcomes compared to APR - Patients treated with LAR demonstrate better local control and overall survival compared to those treated with APR 2
Critical Technical Considerations
To achieve these goals, specific technical principles must be followed:
- Complete mesorectal excision with intact mesorectal fascia - This minimizes local recurrence risk 1
- Preservation of autonomic nerves - Careful dissection preserves urinary and sexual function 1
- Tension-free anastomosis - Mobilization of the left colon and splenic flexure ensures adequate reach 1
- Consideration of colonic pouch construction - This replaces the rectal reservoir and improves functional outcomes 1
Common Pitfalls to Avoid
- Inadequate distal margin - While historically 5 cm margins were advocated, current evidence supports 2 cm as adequate, but this must not be compromised 1
- Incomplete TME - Failure to achieve complete mesorectal excision with intact fascia increases local recurrence risk 1
- Nerve injury - Damage to autonomic nerves compromises the functional preservation goal 1
- Inappropriate patient selection - Attempting LAR when adequate margins cannot be achieved or when sphincter function is already compromised leads to poor outcomes and may necessitate conversion to permanent stoma 6
The 18% overall rate of eventual permanent stoma after LAR (due to anastomotic complications or local recurrence) underscores the importance of careful patient selection and meticulous surgical technique 6.