An abrasion is an injury to the skin in which there is removal of the superficial epithelial layer of the skin (the epidermis) by friction against a rough surface, or destruction of the superficial layers by compression. Antemortem abrasions have a reddish-brown appearance (Figure 4.1) and heal without scarring. Abrasions produced after death are yellow and translucent with a parchment-like appearance. They are important to the forensic pathologist in that they indicate where a blunt instrument or a blunt force has interacted with the body. They may be the only external evidence of trauma to the body. Abrasions are not always present in areas of blunt force injury.

There are three types of abrasions:

1. Scrape or brush abrasions

2. Impact abrasions

3. Patterned abrasions

In scrape (brush) abrasions, the blunt object scrapes off the superficial layers of the skin, leaving a denuded surface. At times, these abrasions may be fairly deep, extending down to the dermis. In such instances, there may be leakage of fluids from vessels with deposit of a serosanguineous fluid on the surface of the abrasion. This dries, forming the familiar reddish brown scab. One of the most common types of scrape abrasions is the linear abrasion known as the scratch. Extensive scrape-like abrasions (graze or sliding abrasions) are seen in pedestrians who slide across the pavement (Figure 4.1 A) after being hit by a motor vehicle. Particles of gravel, dirt, or glass may be embedded in such wounds. An incision made into these areas usually fails to reveal underlying soft tissue hemorrhage (Figure 4.1B). Similar scrape abrasions may be produced when a victim's body is dragged over a rough surface. Nooses or ligatures can also produce scrape abrasions.

It is quite common to read in textbooks of the heaping up of epidermis at the distal end of a scrape abrasion, enabling one to determine the direction of movement of the blunt object or the body across a rough surface. The phenomenon is more theoretical than real and usually does not occur to a significant degree.

Figure 4.1 (A) Scrape-like abrasion from sliding across pavement. (B) Incision shows injury confined to epidermis.

Figure 4.2 Impact abrasions of right side of face.

In impact abrasions, the blunt force is directed perpendicular to the skin, crushing it. Such abrasions tend to be focal and are commonly seen overlying bony prominences where a thin layer of skin covers bone. Impact abrasions over the supraorbital ridge (eyebrow), zygomatic arch (cheekbone), and the side of the nose are commonly seen in individuals who are unconscious when they collapse, and strike their heads on the ground (Figure 4.2).

A patterned abrasion is a variation of an impact abrasion. Here, the imprint of either the offending object, such as a pipe, or intermediary material, such as clothing, is imprinted or stamped on the skin by the crushing effect of the blunt object (Figure 4.3).

Postmortem insect bites and diaper rash are occasionally misinterpreted as abrasions by the inexperienced physician (Figure 4.4A-B). Another artifact that can be confused with an abrasion is drying of the skin of the scrotum and, less commonly, of the vulva (Figure 4.4C). The skin in these areas seems to be very susceptible to drying, especially if exposed to the open air. It has a reddish brown or yellow coloration and may be interpreted as an abrasion.

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