A 35-year-old woman presents with severe pain during and after defecation for 3 weeks, along with visible blood on toilet paper. On examination, a longitudinal tear is seen in the anal canal at the 6 o'clock position. In contrast, her colleague has a chronic anal fistula with purulent discharge and a palpable external opening. Which feature best distinguishes an anal fissure from an anal fistula?

Explanation

## Distinguishing Feature: External Opening vs. Internal Tear **Key Point:** The hallmark discriminator between anal fissure and anal fistula is the presence of an external opening (fistula) versus an internal mucosal tear (fissure). ### Anal Fissure - Longitudinal mucosal tear in the anal canal - No external opening or tract - Severe pain (due to exposed internal sphincter) - Bright red bleeding - Typically at 6 o'clock (posterior) or 12 o'clock (anterior) position - Acute pain during/after defecation ### Anal Fistula - Abnormal tract connecting anal canal to perianal skin - **External opening visible on perianal skin** (pathognomonic) - Purulent or serosanguinous discharge - Chronic intermittent pain (less severe than fissure) - May have internal opening in anal canal - Often follows abscess drainage | Feature | Anal Fissure | Anal Fistula | |---------|--------------|---------------| | **External opening** | Absent | **Present** | | **Internal tract** | No | Yes | | **Discharge** | Blood only | Pus/serosanguinous | | **Pain severity** | Severe | Mild–moderate | | **Bleeding** | Bright red | Minimal | | **Etiology** | Trauma, constipation | Abscess, IBD | **Clinical Pearl:** A palpable external opening on perianal examination is diagnostic of fistula and immediately excludes fissure. **High-Yield:** On NEET PG, if the stem mentions an "external opening" or "tract," the answer is fistula. If it mentions "severe pain" and "tear," think fissure. **Tip:** Fissure = tear (no opening); Fistula = tract (has opening).