Which of the following is the characteristic feature that distinguishes an entrance wound from an exit wound in firearm injuries?

Explanation

## Entrance vs Exit Wounds in Firearm Injuries ### Entrance Wound Characteristics **Key Point:** Entrance wounds have a distinctive **marginal abrasion collar** (also called abrasion rim) formed by the bullet scraping the epidermis as it penetrates the skin. This is the most reliable distinguishing feature. **High-Yield:** Entrance wounds are typically: - Smaller than exit wounds - Circular or oval in shape - Surrounded by an abrasion collar (dark, abraded margin) - May show soot/fouling and powder tattooing at close range - Have inverted (inturned) edges ### Exit Wound Characteristics **Key Point:** Exit wounds lack the abrasion collar because the bullet exits from inside outward, pushing tissue outward rather than scraping it. **High-Yield:** Exit wounds are typically: - Larger and more irregular than entrance wounds - Have everted (outturned) edges - Show beveling of bone (if through skull) - No abrasion collar - No soot or powder tattooing (unless intermediate target involved) ### Comparison Table | Feature | Entrance Wound | Exit Wound | |---------|---|---| | **Size** | Usually smaller | Usually larger | | **Abrasion collar** | Present (diagnostic) | Absent | | **Edges** | Inverted/inturned | Everted/outturned | | **Shape** | Circular/oval | Irregular | | **Soot/fouling** | May be present | Absent (unless ricochet) | | **Powder tattooing** | Present at close range | Absent | | **Bone beveling** | Beveling toward exit | Beveling toward entrance | ### Clinical Pearl **Mnemonic — ABRASION = Entrance:** The **A**brasion collar is the **A**nchor sign for identifying an **E**ntrance wound. ### Mechanism The abrasion collar forms because the bullet's kinetic energy and forward motion scrape away the superficial epidermis as it penetrates, creating a dark rim of abraded skin. This occurs only at entry because the bullet is moving *into* the tissue, not *out of* it.