Low Anterior Resection (LAR) - Detailed Overview

Definition and Context

Fascial Anatomy - The Foundation of Safe Dissection

Fascial relationships of the rectum: (A) male, (B) female - Fischer's Mastery of Surgery

• Fascia propria of the rectum - thin visceral fascia enveloping the rectum and mesorectum; the correct dissection plane is outside this layer
• Denonvilliers' fascia - bilaminar layer anterior to the rectum, separating it from the prostate/seminal vesicles (male) or vagina (female); included with the specimen in cancer surgery
• Presacral (Waldeyer's) fascia - covers the anterior sacrum; dissection deep to this risks catastrophic bleeding from the presacral venous plexus
• Rectosacral fascia - connects presacral fascia at ~S4 to the posterior-inferior rectum; divided close to the presacral fascia during TME
• Lateral stalks - fibrous condensations connecting the rectum to the pelvic sidewall; the middle rectal artery traverses them in ~25% of cases

Pre-operative Evaluation

• Endorectal ultrasound (ERUS) or MRI for staging and defining the circumferential resection margin (CRM)
• Distance from the anorectal ring determines feasibility of LAR vs. abdominoperineal resection (APR)
• Patients with levator or external sphincter involvement are not candidates for sphincter-preserving LAR
• Assessment of fecal continence, comorbidities, and prior radiation
• If patient is at high risk for anastomotic leak, pre-operative marking of a potential stoma site by a Wound, Ostomy, Continence nurse (WOCN)
• For distal tumors: a clear resection margin of ≥2 cm distal bowel is the standard goal; <1 cm may be acceptable for low rectal tumors after chemoradiotherapy (CRT)
• Neoadjuvant CRT (typically 5-FU based + 50.4 Gy radiation) is standard for stage II-III rectal cancers

Surgical Technique (Laparoscopic LAR - Standard Approach)

Step 1 - Patient Positioning and Room Setup

• Modified lithotomy (Lloyd-Davies) position, thighs roughly level with the abdominal wall to avoid interference with lower quadrant instruments
• Surgeon stands on the right side, assistant on the right, scrub nurse on the left
• Camera initially placed left of the patient's hips; moves cephalad as dissection progresses
• Steep Trendelenburg with left side up for left colon and rectal mobilization

Step 2 - Port Placement and Exploration

• 30-degree laparoscope via supraumbilical port
• Three 5-mm trocars: suprapubic, right lower lateral quadrant, left lower lateral quadrant - all lateral to epigastric vessels
• Abdominal exploration to confirm pathology and rule out peritoneal disease

Step 3 - Mobilization of the Left Colon

• Patient in steep Trendelenburg, left side up
• Peritoneum lateral to sigmoid colon is retracted medially, the left peritoneal reflection opened along the white line of Toldt using cautery or scissors
• Left ureter identified at the base of the sigmoidal fossa on the medial aspect - maintaining correct retroperitoneal plane exposes Gerota's fascia
• Splenic flexure mobilization performed if needed for a tension-free anastomosis

Step 4 - Vascular Pedicle Ligation (High Tie)

• Right and perirectal peritoneum scored cephalad to expose the origin of the superior hemorrhoidal and sigmoidal vessels
• Windows developed on either side of the vascular pedicle; both ureters confirmed out of the field
• For cancer: high ligation of the inferior mesenteric artery (IMA) at the aortic bifurcation (or just below the left colic take-off for upper rectal tumors)
• Divided using vascular stapler, Harmonic scalpel, or LigaSure

Step 5 - Mobilization of the Rectum (TME)

• Care to never penetrate the mesorectal fascia (fascia propria)
• Posterior plane: Table tilted right-side up, sigmoid retracted anteriorly and to the right. The presacral space is developed with sharp dissection to the pelvic floor. The hypogastric nerves are identified and gently swept toward the sacrum
• Left lateral plane: Left lateral dissection continued along the lateral aspect of the rectum, meeting the presacral plane
• Anterior plane: Dissection taken above the peritoneal reflection; in cancer, the Denonvilliers' fascia is included with the specimen (anterior plane kept close to posterior vaginal wall / seminal vesicles)
• The lateral stalks are divided to allow deep pelvic exposure for mid-to-low rectal tumors
• Dissection carried to the levator ani level
• Flexible sigmoidoscopy confirms the optimal level of transection

Step 6 - Excision of the Rectum

• Mesorectum divided with LigaSure or Harmonic scalpel, perpendicular to the bowel wall (to avoid a "coning" effect that compromises distal mesorectal clearance)
• Rectum transected with a laparoscopic articulating linear stapler introduced through a small suprapubic incision or hand-port
• Specimen extracted through the supraumbilical incision
• Distal margin: at least 2 cm distal bowel clearance; at least 4 cm distal mesorectal clearance below the tumor

Step 7 - Anastomosis (Colorectal / Coloanal)

1. A purse-string suture is placed in the proximal colon resection margin, and the circular stapler anvil is tied in place
2. Proximal colon returned to the abdomen; incision closed; pneumoperitoneum re-established
3. Circular stapler (25-29 mm) inserted transanally; trocar advanced across (or just in front of) the rectal staple line under laparoscopic visualization
4. Anvil coupled to the shaft; device fired, creating an end-to-end anastomosis
5. Leak test: pelvis filled with saline, rectum insufflated with air via flexible scope, proximal colon occluded with alligator clamp - air bubbles indicate a leak requiring suture reinforcement or diversion

• Extended LAR is used for distal rectal lesions several cm above the sphincter
• Anterior dissection extended to the rectovaginal septum in women, distal to seminal vesicles/prostate in men
• Options: colonic J-pouch (preferred for first 1-2 years function), side-to-end anastomosis (anvil 3-4 cm from stapled end), or straight coloanal anastomosis
• J-pouch and side-to-end anastomosis significantly improve postoperative bowel function for the first 1-2 years without increasing anastomotic complications (supported by multiple RCTs)

Step 8 - Defunctioning Stoma (Selective)

• Low rectal anastomosis (<5 cm from sphincters)
• Neoadjuvant radiotherapy
• Male sex (independent risk factor for leak)
• Technically difficult or tension on anastomosis
• Evidence of leak on intraoperative testing
• Immunosuppression, poor nutritional status

Approaches

Complications

Intraoperative

• Ureteral injury - from failure to identify/protect ureters during vascular ligation or rectal mobilization
• Presacral venous bleeding - life-threatening; occurs when dissection goes deep to presacral fascia; torn vessels retract into sacral foramina making control extremely difficult
• Hypogastric nerve injury - sexual and bladder dysfunction
• Splenic injury during flexure mobilization

Early Postoperative

Late Complications

• Anastomotic stricture - managed by serial dilatation
• Stoma reversal complications (if DLI created)

Low Anterior Resection Syndrome (LARS)

• Increased stool frequency and fragmentation
• Fecal urgency and clustering
• Fecal incontinence
• Incomplete evacuation
• Gas incontinence

1. Loperamide (first-line antidiarrheal)
2. Rectal irrigation (transanal irrigation to aid emptying)
3. Biofeedback / pelvic floor physiotherapy - effective for mild-moderate LARS
4. Sacral nerve stimulation (SNS/Interstim) - 71% success rate at 15 months follow-up (systematic review of 7 studies)
5. End colostomy - for intractable, progressive fecal incontinence

Genitourinary Dysfunction

• Male: Erectile dysfunction, absent/retrograde ejaculation (hypogastric plexus at L5/S1, pelvic parasympathetics at S2-S4)
• Female: Dyspareunia, reduced orgasm
• Bladder: Difficulty emptying, incontinence (injury to inferior hypogastric plexus)

Oncologic Outcomes

• Standard LAR with TME achieves local recurrence rates of <10% compared to >25% with blunt dissection
• Quality of the TME specimen (complete, nearly complete, or incomplete) is a major determinant of local recurrence
• Circumferential resection margin (CRM): positive CRM (≤1 mm) is associated with significantly worse local recurrence and overall survival
• Neoadjuvant CRT downstages T3/T4 tumors, increases R0 resection rates, and reduces local recurrence

Key Surgical Principles Summary

1. Correct fascial plane (outside fascia propria, inside presacral fascia)
2. Protect autonomic nerves (hypogastric nerves posterolateral, pelvic parasympathetics lateral/anterior)
3. Protect ureters throughout dissection
4. Perpendicular mesorectal transection to avoid coning
5. Tension-free, well-vascularized anastomosis - check with leak test
6. Intraoperative colonoscopy to confirm tumor clearance and anastomotic integrity
7. Selective DLI for high-risk anastomoses