Difference Between Low Anterior Resection and Sigmoidectomy
A low anterior resection (LAR) is a surgical procedure specifically for rectal or rectosigmoid cancers that preserves the anal sphincter, while sigmoidectomy is a more limited resection of the sigmoid colon that does not extend into the rectum.
Anatomical Differences
Low Anterior Resection (LAR)
- Targets the rectum or rectosigmoid junction
- Extends distally into the rectum, often to within 2-5 cm of the anal verge
- Requires total mesorectal excision (TME) when treating rectal cancer
- Preserves the anal sphincter complex
- Often requires a more extensive pelvic dissection
Sigmoidectomy
- Targets only the sigmoid colon
- Does not extend into the rectum
- Involves resection of the sigmoid colon with its associated mesocolon
- No involvement of the mesorectum
- Less extensive pelvic dissection required
Indications
Low Anterior Resection
- Primary indication is rectal cancer or rectosigmoid cancer
- Tumors located above the puborectal muscle (approximately 2 cm above) 1
- Requires adequate distal margin (1-2 cm for well-differentiated tumors, >2 cm for poorly differentiated tumors) 1
Sigmoidectomy
- Sigmoid colon cancer
- Sigmoid diverticulitis
- Sigmoid volvulus 2
- Other benign sigmoid pathologies
Technical Considerations
Low Anterior Resection
- Requires mobilization of the rectum with preservation of pelvic autonomic nerves
- Often includes total mesorectal excision for rectal cancer
- Anastomosis is typically lower in the pelvis (colorectal or coloanal)
- Often requires a temporary diverting stoma to protect the anastomosis 2
- More technically challenging due to the narrow confines of the pelvis
Sigmoidectomy
- Involves resection of the sigmoid colon only
- Anastomosis is typically higher (colocolic)
- Usually does not require a protective stoma
- Technically less demanding than LAR
Functional Outcomes
Low Anterior Resection
- Associated with Low Anterior Resection Syndrome (LARS) in approximately 60% of patients (40% major LARS, 20% minor LARS) 3
- LARS symptoms include:
- Increased frequency of bowel movements
- Urgency
- Incontinence
- Difficulty emptying
- Clustering of stools
- Functional outcome is related to the length of the remaining rectal stump 3
Sigmoidectomy
- Generally better functional outcomes than LAR
- Lower rates of bowel dysfunction
- Studies show significantly less difficulty in emptying (32% vs 71%) and incomplete evacuation (32% vs 66%) compared to LAR 4
Surgical Approach Considerations
Both procedures can be performed via:
- Open surgery
- Laparoscopic approach
- Robotic-assisted approach
The choice between these approaches depends on:
- Surgeon expertise
- Patient factors
- Tumor characteristics
- Available resources
Postoperative Care and Complications
Low Anterior Resection
- Higher risk of anastomotic leak due to lower pelvic anastomosis
- Risk of urinary and sexual dysfunction due to potential nerve damage
- Often requires longer hospital stay
- May require management of temporary stoma and eventual stoma reversal
Sigmoidectomy
- Lower risk of anastomotic complications
- Shorter hospital stay (average 4 days) 5
- Less risk of urinary and sexual dysfunction
- Faster return to normal bowel function
Special Considerations
When deciding between these procedures, surgeons must consider:
- Tumor location and stage
- Patient's age and comorbidities
- Anorectal function
- Need for sphincter preservation
- Quality of life implications
For rectal obstruction, a stoma is often preferred over stenting, particularly when neoadjuvant therapy is planned 2. This allows for proper staging and appropriate oncologic treatment without compromising final outcomes.
In emergency settings such as sigmoid volvulus, sigmoidectomy with primary anastomosis or Hartmann procedure may be performed depending on the viability of the colon and the patient's condition 2.
Remember that preservation of pelvic autonomic nerves and careful surgical technique can significantly improve postoperative bowel function in both procedures 4.