Common causes of head injuries include falls, motor vehicle crashes, assaults, and mishaps during sports and recreational activities.
The thick, hard bones of the skull help protect the brain from injury. Also, the brain is surrounded by layers of tissue (meninges) containing cerebrospinal fluid, which cushions the brain. Consequently, most bumps and knocks on the head do not injure the brain. Head injuries that do not affect the brain are considered minor.
Head injuries may cause brain injury (traumatic brain injury, or TBI).
Head injuries include the following:
The brain may not be damaged even when external injuries are severe.
Common causes of head injuries are falls (especially in older adults and young children), motor vehicle crashes, assaults, and mishaps during sports or recreational activities. Mishaps in the workplace (for example, while operating machinery) and firearms also cause head injuries. In 2013, the most common cause of TBIs was falls.
Often, injury is caused by direct impact. However, the brain can be damaged even if the head has not been hit. For example, violent shaking or sudden deceleration can damage the soft brain as it collides with the rigid skull. In such cases, there may be no visible injuries to the head.
A bump may appear on the head. If the scalp is cut, bleeding may be profuse because the scalp has many blood vessels close to the skin surface. Consequently, a scalp injury may appear to be more serious than it is.
Severe head injury
People may have some of the same symptoms as occur with minor head injury. Some symptoms, such as headache, may be more severe.
Also, symptoms often start with a period of unconsciousness that begins at the time of impact. How long people remain unconscious varies. Some people awaken in seconds, while others do not awaken for hours or even days. On awakening, people often are drowsy, confused, restless, or agitated. They may also vomit, have seizures, or both. Balance and coordination may be impaired. Depending on which area of the brain is damaged, the ability to think, control emotions, move, feel, speak, see, hear, and remember may be impaired—sometimes permanently.
Clear fluid or blood may drain from the nose, ears, or both if a person has a fracture at the base of the skull.
Herniation: The Brain Under Pressure
Bleeding or swelling in the brain can cause pressure that forces the brain downward in the skull. The result may be a herniation, in which brain tissue is forced through a small natural opening in the relatively rigid sheets of tissue that separate the brain into right and left compartments and into upper and lower compartments. (These dividers are extensions of the outer layer of tissue covering the brain, the dura mater.) Herniation compresses brain tissue and thus damages it.
The most common type of herniation is a transtentorial herniation. Part of the temporal lobe is forced through the tentorial notch—the opening in the sheet of tissue between the temporal lobe and cerebellum. The pupil of the eye may become dilated and may not constrict in response to light. A transtentorial herniation can have catastrophic consequences, including paralysis, stupor, coma, abnormal heart rhythms, disturbances or cessation of breathing, cardiac arrest, and death.
An injured brain may bleed or swell because fluid accumulates (called cerebral edema). This bleeding and swelling gradually increase the pressure on the brain because the skull cannot expand to accommodate any increase in its contents. As the pressure increases, the person's symptoms worsen and new symptoms appear. The first symptoms of increased pressure within the skull (intracranial pressure) include worsening headache, impaired thinking, a decreased level of consciousness, and vomiting. Later, the person may become unresponsive. The pupils may widen (dilate).
Eventually (usually within a day or two of injury), the increased pressure may force the brain downward, causing a herniation of the brain—an abnormal protrusion of brain tissue through a natural opening between the compartments of the brain. Herniation of the brain can cause coma or even death if too much pressure is put on the brain stem, the lower part of the brain, which controls such vital functions as heart rate and breathing.
Minor head injury
Diagnosis of minor head injuries is based on a person's symptoms and results of the examination.
Injured people are checked for symptoms that indicate brain function could be worsening. These symptoms include the following:
These symptoms may develop hours or sometimes days after the original injury. If these symptoms occur, prompt medical attention is essential.
If a head injury causes loss of consciousness, even briefly, immediate evaluation by a doctor is necessary. If doctors observe symptoms or findings that indicate possible brain injury, computed tomography (CT) or sometimes magnetic resonance imaging (MRI) is done. CT is usually done first because it can detect accumulated blood (hematomas), bruises (contusions), skull fractures, and sometimes widespread nerve damage (diffuse axonal injury). MRI may be useful later to check for diffuse axonal injury, injury to the brain stem (which controls levels of consciousness and vital body functions), and less obvious brain injuries. MRI can also help doctors predict prognosis.
Skull x-rays are rarely helpful.
RECOGNIZING A SERIOUS HEAD INJURY
Most head injuries are not serious. A serious head injury can be recognized based on certain symptoms. Many of these symptoms indicate that brain functioning is worsening. If any of them occur, medical attention should be sought immediately.
Severe head injury
Diagnosis and treatment of severe head injuries are done at the same time.
If the injury may affect other parts of the body (for example, after a motor vehicle crash) or the person is unconscious, an ambulance or 911 (in the United States) should be called.
When the person who may have a severe head injury reaches the hospital, doctors and nurses do a physical examination to determine whether the injury is serious. First, they check vital signs, including heart rate, blood pressure, and breathing. A person who is not breathing adequately may need a ventilator.
Doctors then quickly check the following:
When doctors are sure that the person is not in immediate danger, a complete neurologic examination is done. This examination may help doctors determine the severity and location of the injury.
Doctors examine infants and children thoroughly to check for bleeding in the retina, located at the back of the eye, and other signs of shaken baby syndrome or child abuse.
Doctors periodically check the person to determine whether the person is improving or getting worse.
CT is done to check for possible brain damage. Sometimes MRI is done in addition to CT. X-rays of the skull are usually unnecessary. They can identify skull fractures but reveal very little about brain damage. X-rays or CT of the neck is done when necessary to determine whether the neck is broken.
If doctors suspect that blood vessels are damaged, angiography, CT angiography, or magnetic resonance angiography may be done to obtain detailed images of the blood vessels.
Minor head injury
Most people who have had a minor head injury recover completely, particularly if symptoms of postconcussion syndrome do not develop.
Symptoms of postconcussion syndrome are common during the week after brain injury. They often resolve during the second week. However, sometimes symptoms persist for months or, rarely, years. People who have had a concussion seem to be more susceptible to another one, particularly if the new injury occurs before symptoms from the previous concussion have completely gone away (as may happen in sports-related concussions, often when an athlete who resumes playing too quickly).
Severe head injury
For adults who have had a severe head injury, most recovery occurs within the first 6 months, although some improvement may continue for up to several years. Children tend to recover more fully, regardless of the injury's severity, and they continue to improve for a much longer time.
The eventual consequences of a severe head injury range from complete recovery to permanent problems or disabilities of varying degrees to death.
Common long-term problems include the following:
Recovery of memory after loss of consciousness due to a severe head injury depends on how quickly consciousness is regained. People who regain consciousness in the first week are most likely to recover their memory.
Rarely, a seizure disorder develops after a severe head injury. It usually starts soon after the injury but may develop up to 4 years later.
The type and severity of disabilities depend on where and how badly the brain was damaged. Different areas of the brain control specific functions. Some functions, such as vision and control of arm and leg movements, are controlled by unique areas on one side of the brain. Damage to any of these areas usually causes impairment of the corresponding function and thus permanent disability.
Undamaged areas of the brain sometimes take over functions that were lost when another area was damaged, resulting in partial recovery. However, as people age, the brain becomes less able to shift functions from one area to another. For example, language skills are handled by several parts of the brain in young children but are concentrated on one side of the brain (the left hemisphere) in adults. If the left hemisphere's language areas are severely damaged before age 8, the right hemisphere can assume near-normal language function. However, damage to language areas during adulthood results in permanent disability.
Rehabilitation after a brain injury can help people minimize the effect of most disabilities on function.
Minor head injury
If a head injury is minor and causes no symptoms other than pain at the site of injury, mild analgesics such as acetaminophen may be used. Aspirin or any other nonsteroidal anti-inflammatory drug should not be taken because these drugs may worsen any bleeding in the brain or skull. Doctors use stitches (sutures) or medical staples to close cuts and then apply gauze or bandages.
If people did not lose consciousness or lost it only briefly and if their examination results are normal, they may be discharged home as long as a family member or friend can check them for certain symptoms every few hours during the first 24 hours after the injury. The family member or friend should bring them to the hospital if any of the following potentially serious symptoms develop:
If people have lost consciousness for longer than a few moments or have abnormal examination results, they are usually kept in the emergency department or hospital for observation.
Children who have had a minor head injury may be allowed to sleep, but they should be awakened every few hours and checked for symptoms.
People, including children, are admitted to the hospital if doctors suspect brain damage based on symptoms or CT findings. Children are also admitted to the hospital if they were unconscious even briefly or had a seizure or if child abuse is suspected.
Severe head injury
If the injury may affect other parts of the body (for example, after a motor vehicle crash) or if the person is unconscious, an ambulance should be called. When emergency personnel are moving a person who has had a severe head injury, they take great care to avoid making the injuries worse. The neck should be assumed to be broken until proved otherwise. In such cases, the person's head, neck, and spine are stabilized. Usually, the person is put in a hard neck collar, strapped to a firm board, and carefully padded to prevent movement.
People with severe head injuries are admitted to the hospital, usually to an intensive care or critical care unit.
The first priority is to keep blood pressure and levels of oxygen and carbon dioxide in the blood at desirable levels. If the head injury is severe, the areas of the brain that control breathing may be affected. Also, the reflex that protects the windpipe (trachea) may not be functioning. (This reflex prevents saliva and other substances in the mouth from being inhaled.) For these reasons, a breathing tube is usually inserted through the mouth into the windpipe to help people breathe while doctors treat other problems, such as swelling in the brain. If the head injury is very severe, mechanical ventilation may be used.
Doctors control blood pressure and minimize the amount of brain swelling by adjusting the amount of intravenous fluids given and sometimes by giving intravenous drugs that increase fluid excretion (diuretics, such as mannitol and furosemide) or a concentrated salt solution (hypertonic saline). The concentrated salt solution may help minimize brain swelling more effectively than diuretics. Managing oxygen and carbon dioxide levels in the blood can help relieve pressure within the skull caused by swelling and ensure that the brain is getting enough oxygen. Doctors can control these levels by adjusting the amount of oxygen given and the rate and depth of breaths given by the ventilator. The head of the bed may be raised to prevent excessive pressure within the skull and brain.
A small pressure gauge may be implanted inside the skull to measure pressure within the skull and to determine how well the treatments are preventing or treating pressure elevation within the brain. Alternatively, a catheter may be inserted into one of the spaces (ventricles) within the brain. The ventricles contain cerebrospinal fluid, which flows over the surface of the brain between the layers of tissue that cover the brain (meninges). The catheter can be used to monitor the pressure and to drain cerebrospinal fluid, reducing the pressure within the skull. Sometimes doctors need to surgically open the skull to relieve the pressure.
Pain is treated. Opioid pain relievers may be needed. People may need to be sedated because too much muscle activity can be harmful. Fever is treated. If seizures occur, anticonvulsants are given.
Doctors closely monitor the function of other organs, such as the kidneys, heart, lungs, and intestine because severe head injury can impair function of those organs.