Traumatic Brain Injury
A traumatic brain injury (TBI) is defined as a blow to the head or a penetrating head injury that disrupts the normal function of the brain. TBI can result when the head suddenly and violently hits an object or when an object pierces the skull and enters brain tissue. Symptoms of a TBI can be mild, moderate or severe, depending on the extent of damage to the brain. Mild cases may result in a brief change in mental state or consciousness, while severe cases may result in extended periods of unconsciousness, coma or even death.
Causes include falls, vehicle collisions, and violence. Brain trauma occurs as a consequence of a sudden acceleration or deceleration within the cranium or by a complex combination of both movement and sudden impact. In addition to the damage caused at the moment of injury, a variety of events following the injury may result in further injury. These processes include alterations in cerebral blood flow and the pressure within the skull. Some of the imaging techniques used for diagnosis include computed tomography and magnetic resonance imaging (MRIs).
Traumatic brain injury can have wide-ranging physical and psychological effects. Some signs or symptoms may appear immediately after the traumatic event, while others may appear days or weeks later.
- Loss of consciousness
- Dilated pupils
- Vision changes (blurred vision or seeing double, not able to tolerate bright light, loss of eye movement, blindness)
- Cerebrospinal fluid (CSF) (which may be clear or blood-tinged) coming out of the ears or nose
- Dizziness and balance problems
- Breathing problems
- Slow pulse
- Slow breathing rate, with an increase in blood pressure
- Ringing in the ears or changes in hearing
- Cognitive difficulties
- Inappropriate emotional responses
- Speech difficulties (slurred speech, inability to understand and/or articulate words)
- Difficulty swallowing
- Body numbness or tingling
- Droopy eyelid or facial weakness
- Loss of bowel control or bladder control
When discussing TBI, the term "mass lesion" is often used. This refers to an area of localized injury that may cause pressure within the brain. The most common mass lesions related to TBI are hematomas and contusions.
A hematoma is a blood clot within the brain or on its surface. Hematomas may occur anywhere within the brain. An epidural hematoma is a collection of blood between the dura mater (the protective covering of the brain) and the inside of the skull. A subdural hematoma is a collection of blood between the dura mater and the arachnoid layer, which sits directly on the surface of the brain.
A cerebral contusion is bruising of brain tissue. When examined under a microscope, cerebral contusions are comparable to bruises in other parts of the body. They consist of areas of injured or swollen brain mixed with blood that has leaked out of arteries, veins or capillaries. Contusions are seen most commonly at the base of the front parts of the brain, but they may occur anywhere.
An intracerebral hemorrhage (ICH) describes bleeding within the brain tissue, which may be related to other brain injuries, especially contusions. The size and location of the hemorrhage helps determine whether it can be removed surgically.
TBI can produce microscopic changes that cannot be seen on CT scans that are scattered throughout the brain. This category of injuries is called diffuse brain injury, which may occur with or without an associated mass lesion.
Diffuse axonal injury refers to impaired function and gradual loss of some axons, which are the long extensions of a nerve cell that enable such cells to communicate with each other even if they are located in parts of the brain that are far apart. If enough axons are injured in this way, then the ability of nerve cells to communicate with each other and to integrate their function may be lost or greatly impaired, possibly leaving a patient with severe disabilities.
Another type of diffuse injury is ischemia, or insufficient blood supply to certain parts of the brain. It has been shown that a decrease in blood supply to very low levels may occur commonly in a significant number of TBI patients. This is crucial because a brain that has just undergone a traumatic injury is especially sensitive to even slight reductions in blood flow. Changes in blood pressure during the first few days after head injury can also have an adverse effect.
No treatment is required for most linear skull fractures, which are simple breaks or "cracks" in the skull. Of greater concern is the possibility that forces strong enough to cause a skull fracture may also have caused some damage to the underlying brain. Fractures of the base of the skull are problematic if they cause injury to nerves, arteries or other structures. If a fracture extends into the sinuses, there may be leakage of cerebrospinal fluid (CSF) from the nose or ears. Most leaks will stop spontaneously. Sometimes, however, it may be necessary to insert a lumbar drain, which is a long, thin, flexible tube that is inserted into the CSF space in the spine of the lower back. This provides an alternate route for CSF drainage so that the dural tear that is responsible for the CSF leak in the base of the skull has time to seal.
Depressed skull fractures are those in which part of the bone presses on or into the brain. These may require surgical treatment. The damage caused by depressed skull fractures depends upon the region of the brain in which they are located and also upon the possible coexistence of any associated diffuse brain injury.
Like all trauma patients, persons with TBI need to undergo a systematic yet rapid evaluation in the emergency room. Cardiac and pulmonary function is assessed first. Next, a quick examination of the entire body is performed, followed by a complete neurological examination. The neurological examination includes an assessment utilizing the Glasgow Coma Scale (GCS). In addition to the GCS, the ability of the pupils to become smaller in bright light is also tested. In patients with large mass lesions or with high intracranial pressure (ICP), one or both pupils may be very wide or "blown". The presence of a wide or dilated pupil on only one side suggests that a large mass lesion may be present on the same side as the dilated pupil. Brainstem reflexes including gag and corneal (blink) may also be tested.
Many patients with moderate or severe head injuries are taken directly from the emergency room to the operating room. In many cases, surgery is performed to remove a large hematoma or contusion that is significantly compressing the brain or raising the pressure within the skull. After surgery, these patients are usually observed and monitored in the intensive care unit (ICU).
Other head-injured patients may not go to the operating room immediately, but instead are taken from the emergency room to the ICU. Contusions or hematomas may enlarge over the first hours or days after head injury, so some patients are not taken to surgery until several days after an injury. Delayed hematomas may be discovered when a patient's neurological exam worsens or when their ICP increases. On other occasions, a routine follow-up CT scan that was ordered to determine if a small lesion has changed in size indicates that the hematoma or contusion has enlarged significantly. In many cases, removing the lesion before it enlarges and causes neurological damage may be the safest approach for the patient.
At surgery, the hair over the affected part of the head is usually shaved. After the scalp incision is made, the bone that is removed is usually taken out in a single piece or flap, which is then replaced after surgery. Sometimes, however, the bone may be shattered or heavily contaminated. In these cases, the contaminated or shattered fragments may be removed and not replaced. The dura mater is carefully cut to reveal the underlying brain. After any hematoma or contusion is removed, the neurosurgeon ensures that the area is not bleeding. He or she then closes the dura, replaces the bone and closes the scalp. If the brain is very swollen, some neurosurgeons may decide not to replace the bone until the swelling decreases, which may take up to several weeks. The neurosurgeon may elect to place an ICP monitor or other types of monitors if these were not already in place. The patient is then returned to the ICU for observation and additional care.
At the present time, there is no medication or "miracle treatment" that can be given to prevent nerve damage or promote nerve healing after TBI. The primary goal in the ICU is to prevent any secondary injury to the brain. The "primary insult" refers to the initial trauma to the brain, whereas the "secondary insult" is any subsequent development that may contribute to neurological injury. For example, an injured brain is especially sensitive and vulnerable to decreases in blood pressure that might otherwise be well tolerated. One way of avoiding secondary insults is to try to maintain normal or slightly elevated blood pressure levels. Likewise, increases in ICP, decreases in blood oxygenation, increases in body temperature, increases in blood glucose and many other disturbances can potentially worsen neurological damage. The prevention of secondary insults is a major part of the ICU management of head-injured patients.
Various monitoring devices may assist health care personnel in caring for the patient. Placement of an ICP monitor into the brain itself can help detect excessive swelling of the brain. One commonly used type of ICP monitor is a ventriculostomy, which is a narrow, flexible, hollow catheter that is passed into the ventricles, or fluid spaces in the center of the brain, to monitor ICP and to drain CSF if ICP increases. Another commonly used type of intracranial pressure monitoring device involves placement of a small fiberoptic catheter directly into the brain tissue. Additional catheters may be added that measure brain temperature and brain tissue oxygenation. Placement of an oxygen sensor into the jugular vein can detect how much oxygen in the blood is arising from the brain and can indicate how much oxygen the brain is using. This may be related to the degree of brain damage. Many other monitoring techniques are currently under investigation to see if they can help to improve outcome after head injury or provide other critical information about caring for TBI patients.
One of the most widely used systems to classify outcome from head injury is the Glasgow Outcome Scale (GOS). Patients with mild head injury (usually defined as GCS score on admission of 13-15) tend to do well. They may experience headaches, dizziness, irritability or similar symptoms, but these gradually improve in most cases.
Patients with moderate head injuries fare less well. Approximately 60 percent will make a positive recovery, and an estimated 25 percent will be left with a moderate degree of disability. Death or a persistent vegetative state will be the outcome in about 7 to 10 percent of cases. The remainder of patients will have a severe degree of disability.
The group comprised of severely head-injured patients has the worst outcomes. Only 25 to 33 percent of these patients have positive outcomes. Moderate disability and severe disability each occur in about a sixth of patients, with moderate disability being slightly more common. About 33 percent of these patients do not survive. The remaining few percent remain persistently vegetative.
The above statistics apply to patients with so-called closed head injuries. For penetrating head injuries, which today are caused most commonly by handguns, outcomes follow a different pattern. More than 50 percent of all patients with gunshot wounds to the head who are alive upon arrival at a hospital do not survive because their initial injuries are so severe. However, most of the remaining patients tend to do fairly well, largely because their injuries are relatively mild (GCS score of 13-15). Relatively few patients suffer injuries of intermediate severity (GCS score of 9-12) from gunshot wounds, but it is this group that has the most variability in outcomes.