Penetrating Head Injury - Mechanisms

Mechanisms

In penetrating injury from high-velocity missiles, injuries may occur not only from initial laceration and crushing of brain tissue by the projectile but also from the subsequent cavitation. High-velocity objects create rotations and can create a shock wave that cause stretch injuries, forming a cavity that is three to four times greater in diameter than the missile itself. A pulsating temporary cavity is also formed by a high-speed missile and can have a diameter thirty times greater than that of the missile. Though this cavity is reduced in size once the force is over, the tissue that was compressed during cavitation remains injured. Destroyed brain tissue may either be ejected from entrance or exit wounds or packed up against the sides of the cavity formed by the missile.

Low-velocity objects usually cause penetrating injuries in the regions of the skull's temporal bones or orbital surfaces, where the bones are thinner and thus more likely to break. Damage from lower-velocity penetrating injuries is restricted to the tract of the stab wound, because the lower-velocity object does not create as much cavitation. However, low-velocity penetrating objects such as slow bullets may ricochet inside the skull, continuing to cause damage until they stop moving.