What is lateral internal sphincterotomy?

What is Lateral Internal Sphincterotomy?

Lateral internal sphincterotomy (LIS) is a surgical procedure that involves cutting a portion of the internal anal sphincter muscle through a small incision on the side of the anus to reduce sphincter hypertonia and allow chronic anal fissures to heal. 1, 2

Surgical Technique

• The procedure is performed through a stab incision over the intersphincteric plane, typically using electrocautery 2
• The length of sphincter division should match the length of the fissure 2
• The procedure can be performed under local anesthesia on an outpatient basis without requiring preoperative studies, bowel preparation, or antibiotic prophylaxis 3
• The division is made laterally (on the side) rather than posteriorly to minimize complications 4

Mechanism of Action

• LIS works by permanently reducing internal anal sphincter hypertonia, which is the primary pathophysiologic mechanism underlying chronic anal fissures 3
• By decreasing the resting pressure of the internal sphincter, the procedure improves blood flow to the fissure site and allows healing 3
• Some evidence suggests that fibrosis of the internal anal sphincter contributes to chronic fissure pathogenesis, and LIS addresses this by cutting the fibrotic portion 1

Clinical Efficacy

• LIS is considered the gold standard surgical treatment for chronic anal fissures that fail conservative management, with healing rates of 90-98% 2, 3
• Recurrence rates are low, ranging from 1.3% to 7.5% 1, 3
• The procedure can be successfully repeated on the contralateral side if fissures recur after initial sphincterotomy, with 98% healing rates 2

Complications and Risks

• The overall complication rate is approximately 4%, with the most concerning being incontinence 1
• Gas incontinence occurs in 0.4-7.5% of patients initially, though this often improves over time (dropping to 5% at six months) 1, 3
• Other complications include delayed healing (3%), perianal abscess (0.6%), hematoma (2.5%), and hemorrhage (2.5%) 1, 3
• Manual anal dilatation should be avoided entirely as an alternative, as it carries a 30% temporary and 10% permanent incontinence rate 5

Important Considerations

• Patients may develop neuropathic dysesthesia and altered sensations after LIS, which typically represent pelvic floor muscle tension rather than structural sphincter damage 5, 6
• These sensory complications are often underrecognized but can affect both continence sensations and sexual function 5, 6
• Botulinum toxin injection represents a safer alternative to LIS, achieving 75-95% cure rates with no risk of permanent incontinence or sexual dysfunction 6

Tailored Approaches

• Calibrated sphincterotomy divides the sphincter based on manometry results: 20% division for mild hypertonia (50-60 mmHg), 40% for moderate (60-80 mmHg), and 60% for severe (>80 mmHg) 7
• Minimal LIS techniques that cut only the fibrotic portion show excellent outcomes with only 0.4% gas incontinence rates 1