A penetrating head injury, or open head injury, is a head injury in which, at minimum the dura mater — the outer layer of the meninges — is breached. Penetrating injuries can be caused by 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 frequently cause irreversable brain damage, permanent disability, or death.
A penetrating head injury involves "a wound in which an object breaches the cranium but does not exit it." In contrast, a perforating head injury is a wound in which the object passes through the head and leaves an exit wound. Tangential head injuries refer to incidents where an object induces trauma to the head in such a way that, while it may bounce off the skull, the impact nevertheless is forceful enough to push pieces of the skull into the brain.
Cause
thumb|right|upright|3-D CT scan showing a penetrating head injury by a screwdriver
thumb|An 1868 illustration showing the perforating head injury of [[Phineas Gage, a railroad worker who had a tamping iron driven through his skull in an 1848 accident.]]
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.
Pathophysiology
Though it is more likely to cause infection, penetrating trauma is similar to closed head injury such as cerebral contusion or intracranial hemorrhage. As in closed head injury, intracranial pressure is likely to increase due to swelling or bleeding, potentially crushing delicate brain tissue. Most deaths from penetrating trauma are caused by damage to blood vessels, which can lead to intracranial hematomas and ischemia, which can in turn lead to a biochemical cascade called the ischemic cascade. The injury in penetrating brain trauma is mostly focal (that is, it affects a specific area of tissue).
While blunt trauma to the head does not present a risk of shock due to hemorrhage, penetrating head trauma does.
Diagnosis and treatment
A person with a penetrating head injury may be evaluated using X-ray, CT scan, or MRI (MRI can only be used when the penetrating object would not be magnetic, because MRI uses magnetism and could move the object, causing further injury). A study published in 1991, which documented 314 individuals who had had penetrating cranial injuries caused by gunshot wounds, found that 73% died from their injuries at the scene of the incident, and a further 19% ultimately died later, thus indicating a total mortality rate of 92%. Up to 50% of patients with penetrating brain injuries get late-onset post-traumatic epilepsy.
See also
- Brain herniation
- Traumatic brain injury