In which case is a low anterior resection (LAR) typically performed for rectal cancer?

Low Anterior Resection for Rectal Cancer

Low anterior resection is performed for cancer in the rectosigmoid junction (option d), as these tumors are located in the upper portion of the rectum. 1

Anatomical Considerations for Surgical Decision-Making

• Low anterior resection (LAR) is the treatment of choice for lesions in the mid to upper rectum, including the rectosigmoid junction, as recommended by the National Comprehensive Cancer Network 1
• For tumors in the lower rectum (options a, b, c, and e), other surgical approaches are typically required, such as abdominoperineal resection or coloanal anastomosis 1
• Cancers distal to the dentate line (option e) would require abdominoperineal resection as sphincter preservation is not possible 1
• Cancers involving the internal anal sphincter fibers (option c) would also not be suitable for LAR due to the need for sphincter removal 1

Technical Considerations for Low Anterior Resection

• To achieve satisfactory tumor clearance with LAR, a safe margin of at least 2 cm between the lower end of the tumor and the rectal stump must be maintained 1
• Patients with tumors located 2 cm above the puborectal muscle by digital examination can undergo low anterior resection 2
• For differentiated cancers and localized tumors of stage T2 or less, distal surgical margins should be at least 1 cm from the tumor 2
• For poorly differentiated cancers and tumors of stage T3 or greater, distal surgical margins should be more than 2 cm with total mesorectal excision (TME) 2

Contraindications for Low Anterior Resection

• LAR is contraindicated in patients with poor anorectal function and advanced age 2
• Cancer starting from the dentate line and extending 8 cm proximally (option a) would typically require abdominoperineal resection rather than LAR 1
• Cancer 5 cm proximal to the dentate line (option b) may be considered for ultralow anterior resection with coloanal anastomosis rather than standard LAR, especially if it's in the lower third of the rectum 3, 4

Functional Outcomes After Low Anterior Resection

• Patients undergoing LAR, particularly ultralow anterior resection, often experience significant bowel dysfunction including fecal incontinence 4, 5
• Risk factors for major Low Anterior Resection Syndrome (LARS) include advanced age (>70), male sex, ultralow anterior resection, and chemoradiation therapy 4
• The 5-year survival rate for patients undergoing LAR with coloanal anastomosis is approximately 73%, with pelvic recurrence rates around 11% at 5 years 6

Common Pitfalls and Caveats

• Attempting LAR for tumors too close to the dentate line can compromise oncological outcomes and lead to poor functional results 1, 5
• Inadequate distal margins increase the risk of local recurrence, which is a primary cause of requiring permanent colostomy after attempted sphincter preservation 6
• While sphincter preservation is desirable, severe fecal incontinence after ultralow anterior resection can be more debilitating than a well-functioning colostomy 5
• Pelvic recurrence after LAR is associated with histopathologic markers of aggressive disease rather than short distal margins 6