A 32-year-old woman presents with severe anal pain during and after defecation for the past 3 weeks. She reports bright red blood on toilet paper and describes the pain as sharp and burning, lasting 1–2 hours after each bowel movement. On examination, a visible tear is noted in the posterior midline of the anal canal. Digital rectal examination is extremely painful and cannot be completed. She denies fever, perianal discharge, or a history of inflammatory bowel disease. What is the most likely diagnosis?

Explanation

## Diagnosis: Acute Anal Fissure **Key Point:** An acute anal fissure is a longitudinal tear in the anoderm (distal to the dentate line) that presents with severe pain out of proportion to the physical findings, bright red bleeding, and visible tear on inspection. ### Clinical Features of Acute Fissure | Feature | Acute Fissure | Chronic Fissure | |---------|---------------|----------------| | **Duration** | < 6 weeks | > 6 weeks | | **Pain severity** | Severe, sharp, burning | Severe but patient may adapt | | **Visible tear** | Clean, sharply demarcated | Indurated edges, sentinel pile, internal skin tag | | **Bleeding** | Bright red, minimal | Minimal or absent | | **Location** | 90% posterior midline, 10% anterior | Posterior > anterior | | **Sphincter tone** | Normal or mildly elevated | Markedly elevated (internal sphincter hypertonia) | ### Pathophysiology Most fissures occur in the posterior midline because: 1. The anoderm is thinnest posteriorly 2. Blood supply is poorest in the posterior commissure 3. Internal anal sphincter tone is highest posteriorly **High-Yield:** The combination of **severe pain**, **visible tear on inspection**, **bright red bleeding**, and **posterior midline location** is pathognomonic for acute anal fissure. ### Management of Acute Fissure 1. **Medical management (first-line):** - Stool softeners (docusate) - High-fiber diet - Sitz baths (15–20 min, 3–4 times daily) - Topical anesthetics (lignocaine 2%) - Topical sphincter relaxants: diltiazem 2% or nifedipine 0.5% (reduces internal sphincter pressure) 2. **Surgical intervention (if medical management fails after 6–8 weeks):** - Lateral internal sphincterotomy (gold standard) - Botulinum toxin injection (temporary, for high-risk patients) **Clinical Pearl:** The severe pain in acute fissure is due to internal anal sphincter spasm and mucosal ulceration, not the tear itself. This is why sphincter-relaxing agents are so effective. **Warning:** Digital rectal examination in acute fissure is often impossible due to pain and sphincter spasm — diagnosis is made on visual inspection alone.