A 48-year-old man with a 10-year history of chronic anal fissure (posterior midline) presents for surgical evaluation after failure of medical management with topical diltiazem and stool softeners for 8 weeks. On examination, the fissure has indurated edges, a sentinel pile at the anal verge, and an internal skin tag. Internal anal sphincter pressure is markedly elevated on manometry. He is concerned about postoperative incontinence. What is the most appropriate surgical intervention?

Explanation

## Diagnosis: Chronic Anal Fissure — Surgical Management **Key Point:** Lateral internal anal sphincterotomy (LIAS) is the gold-standard surgical treatment for chronic anal fissure refractory to medical management. It divides the internal anal sphincter to reduce hypertonicity and improve blood flow to the fissure. ### Why Lateral Internal Anal Sphincterotomy? **High-Yield:** The pathophysiology of chronic fissure centers on **internal anal sphincter hypertonia**, which: 1. Reduces blood flow to the posterior commissure (already poorly perfused) 2. Perpetuates pain and prevents healing 3. Maintains the cycle of spasm and ulceration Lateral sphincterotomy directly addresses this mechanism by reducing sphincter pressure. ### Surgical Technique & Safety Profile ```mermaid flowchart TD A[Chronic anal fissure<br/>refractory to medical Rx]:::outcome --> B{Surgical intervention<br/>indicated?}:::decision B -->|Yes| C[Lateral internal<br/>anal sphincterotomy]:::action C --> D[Divide internal sphincter<br/>laterally, 1/2 to 2/3 length]:::action D --> E[Healing rate 90-95%]:::outcome D --> F[Incontinence risk < 5%]:::outcome B -->|No| G[Continue medical Rx]:::action ``` ### Comparison of Surgical Options | Procedure | Mechanism | Healing Rate | Incontinence Risk | Indications | |-----------|-----------|--------------|-------------------|-------------| | **Lateral internal sphincterotomy** | Divide internal sphincter laterally | 90–95% | < 5% | **Gold standard for chronic fissure** | | **Fissurectomy + primary closure** | Excise fissure, close defect | 60–70% | Variable | Rarely used; high recurrence | | **Anoplasty/advancement flap** | Advance healthy tissue over fissure | 80–90% | < 2% | Alternative for anterior fissure or failed LIAS | | **External sphincterotomy** | Divide external sphincter | Not recommended | High (> 20%) | **Contraindicated — risk of severe incontinence** | **Clinical Pearl:** Lateral sphincterotomy is performed on the lateral side (3 or 9 o'clock position) rather than posteriorly to avoid damaging the external sphincter and minimize incontinence risk. The internal sphincter is divided for approximately half to two-thirds of its length. ### Outcomes of Lateral Internal Sphincterotomy - **Healing rate:** 90–95% - **Recurrence:** 5–10% - **Incontinence (any degree):** 5–10% (usually transient) - **Incontinence (significant):** < 1–2% - **Patient satisfaction:** > 90% **Warning:** External anal sphincterotomy is contraindicated because it carries a high risk of permanent fecal incontinence (> 20%). The external sphincter is responsible for voluntary continence; dividing it causes unacceptable morbidity. ### Why Other Options Are Incorrect **Fissurectomy with primary closure:** - Does not address the underlying sphincter hypertonia - High recurrence rates (30–40%) - No longer recommended as monotherapy **Anoplasty with advancement flap:** - Reserved for anterior fissures or failed LIAS - More complex, longer operative time - Not first-line for posterior fissure **External anal sphincterotomy:** - Unacceptable incontinence rates - Only mentioned as a "trap" option in exams