Penetrating injury can be caused by missiles (high-velocity projectiles) or objects of lower velocity such as knives or bone fragments from a skull fracture that are driven into the brain. Head injuries caused by penetrating trauma are serious medical emergencies and may cause permanent disability or death.
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 centrifugal forces 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 (Vinas and Pilistis, 2004). 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 (Vinas and Pilistis, 2004). 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 enterance or exit wounds or packed up against the sides of the cavity formed by the missile (Vinas and Pilistis, 2004).