Types of Brain Injury
There are two broad classifications of traumatic brain injury: open and closed. Open head injury occurs when the skull is penetrated by a sharp instrument (such as a knife) or an explosive missile (such as a bullet or shell fragments). In penetrating head injuries, tissue damage will be found at the point of penetration and surrounding the path of the intruding object. Consequences of an open head injury can be swelling, lacerations from skull fragments, and vulnerability to infection and further injury.
Closed head injury is primarily caused by a blunt impact or blow to the head without penetrating the skull. The most common form of brain damage is caused by closed head injury. Consequences of a closed head injury can be swelling, increased intercranial pressure, and tissue compression.
More specific types of brain injury are:
A laceration or tearing of the brain, usually from a skull fracture or gunshot wound, results in rupture of large blood vessels with bleeding into the brain and subarachnoid space. This can result in hematomas, edema and increased intercranial pressure. Objects (e.g. bullets) can also ricochet within the skull, which can widen the area of damage.
A coup-contrecoup injury describes contusions that are both at the site of the impact and on the complete opposite side of the brain.
A contusion is a visible bruise (bleeding) on the brain.
Hematomas are a swelling or mass of blood in the brain caused by a break in a blood vessel. An epidural hematoma is above the dura mater, a subdural hematoma beneath the dura, subarachnoid between the arachnoid membrane and the pia mater, and intracerebral a hemmorrhage localized to one area of the brain.
Diffuse Axonal Injury (DAI) is caused by strong rotational forces of the head, such as with a car accident. The unmoving brain lags behind the movement of the skull, causing brain structures to tear. There is extensive tearing of nerve tissue throughout the brain which can disrupt the brain's regular communication and chemical processes. This "chemical cascade" can cause additional injury.
Concussions are caused when the brain receives trauma from an impact, sudden momentum or movement change. The blood vessels in the brain may stretch and cranial nerves may be damaged. A person may or may not experience a brief loss of consciousness (not exceeding 20 minutes). They may remain conscious, but feel "dazed"
Anoxic brain injury occurs when the brain does not receive any oxygen. Cells in the brain need oxygen to survive and function.
Hypoxic brain injury results when the brain receives some, but not enough oxygen.