One type of brain injury is a traumatic brain injury (TBI), in which sudden trauma impacts the skull, causing damage to the brain. In the United States, about 1.7 million people each year experience a TBI, according to the Centers for Disease Control and Prevention (CDC). Two categories of TBI exist: a closed injury and a penetrating injury. With a closed injury, the trauma does not penetrate the skull. The force from this trauma causes the brain to move, which results in bruising (contusion) and bleeding (hemorrhage) in the brain. With a penetrating injury, the trauma causes the skull to break and an object can directly damage the brain tissue. The leading causes of a TBI according to the CDC include falls (35.2 percent), motor vehicle accidents (17.3 percent), being struck by an object or being struck against an object (16.5 percent), and assaults (10 percent).
When the nerves in the brain become stretched or torn due to the impact, a type of brain injury called diffuse axonal injury (DAI) may occur. The Ohio State University Medical Center explained that with a DAI, the torn nerves die and the damage can affect multiple areas of the brain. Bleeding in the brain can damage the brain, whether it results from an impact to the brain or it is from a burst cerebral aneurysm. A cerebral aneurysm, which is a bulge that forms on the artery's wall in the brain, grows slowly and can rupture. This type of aneurysm can form due to damage to the artery's wall after a head injury, high blood pressure or be congenital. Bleeding in the brain can occur over the surface of the brain (subarachnoid hemorrhage), into the brain tissue (intracerebral hemorrhage) and in the ventricles of the brain (intraventricular hemorrhage). Some patients may have a hematoma, which is a collection of blood in the brain. The Ohio State University Medical Center noted that a hematoma can form right after sustaining a head injury or after some time. The different types of hematoma include an intracerebral hematoma, in which the collection of blood is inside the brain tissue; a subdural hematoma, in which the collection of blood is between the dura mater (the outermost meninges covering the brain) and the brain; and an epidural hematoma, in which the collection of blood is between the skull and the dura mater.
Another type of brain injury is a hypoxic-anoxic injury (HAI), in which oxygen to the brain becomes disrupted. With a hypoxic brain injury, there is a partial lack of oxygen, while with an anoxic brain injury, there is a total lack of oxygen, according to the Family Caregiver Alliance. Oxygen flow to the brain can be disrupted by exposure to certain toxins, such as carbon monoxide. Conditions that increase a person's risk of developing anoxic brain damage include cardiac arrest, drug use, electrical shock, heart attack, stroke, choking and suffocating, according to the NYU Langone Medical Center. The Better Health Channel added that diseases that affect the brain, such as Parkinson's disease, Alzheimer's disease and multiple sclerosis can also result in a brain injury.