There are many different types of brain injuries, with many different causes, and a wide range of physical, psychological, emotional, and behavioral consequences. It is now recognized that even “mild” concussions can cause serious brain injuries, especially if they occur repeatedly. Profound brain damage can be fatal.
Traumatic brain injury (TBI), skull fracture, bruising or tearing of brain tissue, or blood clots or bleeding between the skull and brain—subdural hematoma and subarachnoid hemorrhage, respectively— can all damage the brain. A slight blow to the head or even a fall without hitting the head may be sufficient to tear blood vessels in the brain. TBI is the most common cause of coma and subarachnoid hemorrhage. Subarachnoid hemorrhage is an accumulation of blood that compresses the brain as the brain swells, damaging tissue. It occurs with 23%–39% of severe head injuries and is frequently fatal. It can also lead to stroke, seizures, or permanent brain damage. Cerebral edema is swelling caused by excessive fluid in the brain from TBI, stroke, or a tumor. Because the skull leaves very little room for brain swelling, cerebral edema is also referred to as elevated intracranial pressure (ICP). ICP can directly damage or destroy brain cells, displace brain tissue, or cause intracerebral hemorrhaging or disrupted blood flow that deprives the brain of oxygen. Edema can prevent fluids from exiting the brain, thereby increasing swelling and ICP. Cerebral edema can very quickly lead to temporary or permanent brain damage or death.
Concussion—the most common TBI—is considered a complex neurobehavioral syndrome. Concussion occurs when the brain jars against the skull with sufficient force to cause temporary loss of function in higher brain centers. The brain movement may be a sudden acceleration, deceleration, and/or rotation. Concussion can be caused by direct or indirect blows to the head or body, violent shaking, whiplash-type injuries, gunshot wounds, or shockwaves from explosions. The actual injury is usually on the opposite side of the head from the initial blow. Concussions may cause a brief loss of consciousness or a dazed feeling. They can also involve skull fracture, bleeding in the brain, diffuse axonal injury (tearing of nerve tissue), or cerebral edema, with temporary or permanent damage. It is not known exactly how brain cells are affected by concussion, but it appears to involve chemical changes that temporarily affect function. During this period of abnormal function, the brain is much more susceptible to a second injury. Although most concussions resolve on their own without lasting effects, even a very mild concussion followed by a second blow to the head before full recovery can have serious, long-lasting consequences—a condition known as second-impact syndrome. The second impact or recurrent TBI is more likely than the initial TBI to cause brain swelling and widespread damage.
There are other types of TBI:
Non-traumatic brain injuries are sometimes called acquired brain injuries. They can include injuries from:
Brain injuries can also occur before or during birth. For example, cerebral palsy can be caused by damage to the motor control centers in the brain before, during, or after birth, resulting in a spectrum of movement disorders.
Most people experience some form of head injury at least once in their lives, although most are not serious. Nevertheless, about 70% of all accidental deaths and most disabilities following trauma are due to brain injuries. Young children, males aged 15–24, and people over age 75 are most likely to suffer head trauma.
There are about 2.5 million TBIs in the United States each year, of which 75% are concussions or other relatively mild forms. Every year in the United States, TBI results in approximately 373,000 hospitalizations, more than 56,000 deaths, and 99,000 permanent disabilities. Sports-related concussion and other TBIs are now recognized as serious public-health concerns. Studies have shown that approximately one out of every five high-school football players suffers a concussion or more serious brain injury during their brief careers. Approximately 230,000 American military personnel suffered “mild” TBIs between 2001 and 2014, primarily from blasts. Falls account for about 40% of all non-combatrelated TBIs. Motor-vehicle accidents account for about 14%. Other common causes of TBIs are bicycle accidents, assaults, and workplace accidents. Firearms cause the most deaths from TBI, and the overall death rate for TBIs from bullets is 91%.
Signs and symptoms of brain injuries depend on the parts of the brain that are damaged. For example, damage to the frontal lobes can cause difficulties with attention, problem-solving, creativity, and other cognitive functions. Symptoms of brain injuries may include:
Symptoms of even a “mild” brain injury may persist for days or weeks. Up to 60% of people with mild brain injuries continue to experience a range of symptoms—post-concussion syndrome—for as long as six months or a year. The severity of symptoms appears to be significantly influenced by previous head injuries and their recovery times and the patient's age.
The neurological exam assesses:
Imaging of the brain by computed tomography (CT), magnetic resonance imaging (MRI), or positron emission tomography (PET), as well as electroencephalography (EEG) and other studies, may help diagnose brain injuries. Cerebral angiography is used to locate damaged blood vessels. However, CT, MRI, EEG, and routine neurologic evaluations may all be normal, because it is difficult to detect microscopic damage with diffuse axonal injuries. Mental status evaluations are particularly important when other neurologic and imaging results are normal. Sometimes small changes in memory or other intellectual abilities are the only indication of a problem.
Brain injuries such as concussions are managed with complete physical and mental rest until symptoms are completely gone. Returning to activities can worsen symptoms, prolong recovery, and put the patient at risk for second-impact syndrome. Normal activities are resumed very gradually in a stepwise manner.
Cerebral edema is commonly treated with corticosteroids, diuretics, glycerin, or other medications. Surgery may be required to measure or relieve ICP, close a vein, drain blood or fluid, or remove a clot. A penetrating head wound or skull fracture may also require surgery. Anticonvulsants can prevent or control seizures. Sedatives and medications for pain, nausea, and vomiting are administered as needed. Transcranial magnetic stimulation has had some success in reviving coma patients with severe TBI. Patients with severe brain injuries may need to relearn basic skills.
With proper rest and management, concussions usually resolve within a few weeks, without lasting neurologic effects. However, symptoms can sometimes last for months, and complete recovery from a more severe concussion may take years. Concussions that are not managed with physical and mental rest can lead to permanent problems. The risk of a second concussion is greater than the risk for the first concussion. Frequent concussions, as experienced by boxers and football and hockey players, can lead to chronic, progressive disorders such as CTE, Parkinson disease and other motor problems, Alzheimer's, disease, or post-traumatic dementia.
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