What is the primary characteristic that distinguishes an entrance wound from an exit wound in a gunshot injury?

## Distinguishing Entrance from Exit Wounds ### Key Morphological Features **Key Point:** The **abrasion collar** (also called the contusion collar) is the most reliable single feature to identify an entrance wound. It is formed by the bullet scraping away the epidermis as it enters the skin under pressure. **High-Yield:** The abrasion collar: - Is present in the majority of entrance wounds - Forms due to the bullet's mechanical pressure and friction against the skin - Is typically absent in exit wounds (though exceptions exist in tangential exits) - Is visible even in contact and close-range shots ### Comparison of Entrance vs. Exit Wounds | Feature | Entrance Wound | Exit Wound | |---------|----------------|------------| | **Abrasion collar** | Usually present | Absent (usually) | | **Size** | Often smaller | Often larger (due to temporary cavity) | | **Edges** | Bevelled inward (funnel-shaped) | Bevelled outward; may be stellate or irregular | | **Tissue tags** | Directed inward | Directed outward | | **Soot/powder** | May be present (range-dependent) | Absent | | **Tattooing** | Present (intermediate range) | Absent | **Clinical Pearl:** Exit wounds are often larger and more irregular because the temporary cavity expands outward, and the bullet may have deformed or fragmented by the time it exits. **Mnemonic:** **ABET** = **A**brasion collar (entrance), **B**evelled inward (entrance), **E**xit is bevelled outward, **T**issue tags point outward (exit).