Definitions of LAR and TME in Rectal Cancer Surgery
LAR (Low Anterior Resection) is a sphincter-preserving surgical procedure that removes the rectum while maintaining anal function, typically used for mid-to-upper rectal cancers, while TME (Total Mesorectal Excision) is the standardized surgical technique involving en bloc removal of the mesorectum with its surrounding fascia, lymphatics, and vessels through sharp dissection.
Low Anterior Resection (LAR)
LAR is the treatment of choice for lesions in the mid to upper rectum, involving resection extended 4 to 5 cm below the distal edge of the tumor, followed by creation of a colorectal anastomosis 1. This approach:
- Preserves sphincter function and avoids permanent colostomy when anatomically feasible
- Requires adequate distal clearance while maintaining anal continence
- May be combined with coloanal anastomosis when anal function is intact and distal clearance is adequate 1
The procedure can be performed via multiple approaches including open laparotomy, laparoscopy, robot-assisted surgery, or transanal techniques 2.
Total Mesorectal Excision (TME)
TME is the gold standard surgical technique recommended for all transabdominal rectal cancer resections 1. The technique involves:
- En bloc removal of the mesorectum including associated vascular and lymphatic structures, fatty tissue, and mesorectal fascia as a complete "tumor package" 1
- Sharp dissection designed to spare autonomic nerves 1
- Radical removal of lymphatic drainage regions of tumors located above the level of the levator muscles 1
Key Technical Principles
The TME approach recognizes that lymphatic drainage patterns vary by tumor location:
- Distal tumors: Both upward and lateral lymphatic drainage
- Proximal tumors: Predominantly upward mesorectal drainage 1
Wide TME is recommended to facilitate adequate lymphadenectomy and improve the probability of achieving negative circumferential margins 1.
Combined Application
LAR is routinely performed using TME technique for optimal oncologic outcomes 1. When the tumor directly involves the anal sphincter or levator muscles, or when margin-negative resection would result in incontinence, an abdominoperineal resection (APR) with TME is performed instead, necessitating permanent colostomy 1.
The quality of TME specimens should be scored according to standardized criteria from the Dutch Rectal Cancer TME Trial 1.