Head Injury

Epidemiology

Head injury is a major public health problem. It occurs most commonly in teenagers and young adults who would otherwise have been productive members of society. The disabilities that many of them incur from their head injuries often make them dependent upon rehabilitation services and other special care needs for the rest of their lives. Although head injuries steal away more potentially productive years than such common illnesses as cancer, AIDS, heart disease, and diabetes, less research money is spent on head injury than on these other diseases.

Head injury is also commonly referred to as traumatic brain injury (TBI). The most common cause of TBI is motor vehicle accidents. This is also the most common mechanism in teenagers and young adults. The next most common cause is a fall, and this mechanism is most common at the extremes of age, i.e., pediatric and geriatric patients. Alcohol or other drug use contributes significantly to the occurrence of many head injuries.

Pathology

Treatment for head injury may be either surgical or nonsurgical. However, these treatments are not mutually exclusive. Many of the same biochemical events that cause damage of the brain after nonoperative TBI also occur in patients who undergo surgery, and an operation may not be able to stop or reverse these underlying processes.

Surgical lesions

When discussing head-injured patients, neurosurgeons often use the term "mass lesion", which refers to an area of localized injury that may cause pressure within the brain. The most common mass lesions seen after TBI are hematomas and contusions. A hematoma is a blood clot within the brain or on its surface. A contusion may be thought of as an area of "bruised" brain. 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.

Hematomas and contusions can occur anywhere within the brain. Those hematomas between the skull and the dura, which is a thick membrane that surrounds the brain, are called epidural hematomas.

Intracerebral hematomas are blood clots that are located within the brain tissue itself.

Contusions are seen most commonly at the base of the front parts of the brain, but they can occur anywhere.

Subarachnoid hemorrhage appears as diffuse blood spread thinly over the surface of the brain. This is seen commonly after head injury. If this is the only abnormality present on a CT scan, then observation for a short period may be the only treatment needed.

Diffuse injuries

The hematomas and contusions described above generally occur in only one or a few specific parts of a patient's brain, and they are usually easily seen on a computerized tomography (CT) scan. However, TBI can also produce microscopic changes that cannot be seen on CT scans and that are scattered throughout the brain. This category of injuries is called diffuse brain injury, which can occur with or without an associated mass lesion.

One type of diffuse brain injury is diffuse axonal injury. This 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 drop in blood supply to very low levels may occur commonly in a significant percentage of head-injured patients. This is important because a brain that has just undergone a traumatic injury is especially sensitive to even slight reductions in blood flow. For the same reason, changes in blood pressure during the first few days after head injury can have an adverse effect.

Skull Fractures

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 worrisome 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 such leaks will stop spontaneously. Sometimes, 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 of 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.

Assessment

Like all trauma patients, persons with head injury need a systematic yet rapid evaluation in the emergency room. Cardiac and pulmonary function are the first priority. Next, a rapid examination of the entire body is performed.

Neurological examination

An accurate neurological examination is important to categorize the severity of a patient's injuries and to plan further evaluation and possible treatment. The standard for objectively assessing the severity of head injury is the Glasgow Coma Scale (GCS) (See below - Table 1). This scale assigns points to each patient based upon three categories: verbal function, eye opening, and best motor (movement) response. Patients with a GCS score of 13-15 are usually classified as having mild head injuries. Those with a GCS score of 9-12 have moderate head injuries, and those with a score of 3-8 are usually described as having severe head injuries. Any patient who is not obeying commands (for example, to follow instructions to hold up two fingers) is also often considered to have a severe head injury, even if the GCS score may be slightly higher than eight.

In addition to the GCS, the ability of the pupils to become smaller in bright light is also important after head injury. 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.

Radiologic assessment

CT scanning is the gold standard for the radiologic assessment of a head-injured patient. A CT scan is easy to perform and is an excellent test for detecting the presence of blood and fractures, which are the most important lesions to identify in emergency situations. Plain x-rays of the skull are recommended by some people as a way to evaluate patients with only mild neurologic dysfunction. However, most centers in the United States have readily available CT scanning, which is a more accurate test. For this reason, the routine use of skull x-rays for head-injured patients has declined.

Magnetic resonance imaging (MRI) is not commonly performed for acute head injury because it takes longer to perform an MRI scan than a CT scan, because MRI is not as useful as CT for acute trauma, and because transporting an acutely injured patient from the emergency room to the MRI scanner is difficult. However, after a patient has stabilized, MRI may demonstrate the existence of lesions that could not be detected by CT. Such information is generally more useful for determining prognosis than for influencing treatment.

Treatment

Surgical

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 first taken from the emergency room to the ICU. However, contusions or hematomas may enlarge over the first hours or days after head injury, so that some patients are not taken to surgery until several days after an injury. Sometimes these delayed hematomas are discovered when a patient's neurologic exam worsens or when the ICP increases. On other occasions, a routine follow-up CT scan that was ordered to see if a small lesion has changed in size indicates that the hematoma or contusion has enlarged significantly. In many of these cases, removing the lesion before it enlarges and causes neurologic damage may be safest for the patient.

Figure 1a-d - Illustrations of surgery for gunshot wound to the head. The hair is first shaved and the incision is mapped out. B) After the scalp incision, an opening is made in the skull. C) The dura is opened. D) Foreign material, blood, and dead tissue are carefully removed. Bleeding is stopped. E) The dura is closed. Parts of the bone may not be replaced if they appear to be contaminated from the bullet wound.
reproduced with permission from Narayan RK: Head injury, in Grossman RG, Hamilton WJ (eds): Principles of Neurosurgery. New York: Raven Press, 1991, pages 259 and 263.

Figure 2a-c - Surgery for a subdural hematoma. A) The hair is shaved. In many cases, a short incision is made just in front of the ear. The thin bone in this area can be removed quickly. The dura is opened, and as much hematoma as possible is removed through this small opening. This may buy enough time to complete the remainder of the opening. B) After the remainder of the skin incision is completed, a piece of the skull is then removed, often by making several burr holes and then connecting these holes with a special saw. C) The dura is opened. The subdural hematoma is carefully removed. All bleeding is stopped. The dura is closed, and the bone is replaced and secured. The scalp is then closed.
reproduced with permission from Narayan RK: Head injury, in Grossman RG, Hamilton WJ (eds): Principles of Neurosurgery. New York: Raven Press, 1991, pages 259 and 263.

At surgery, the hair over the appropriate part of the head is 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 next structure encountered is the dura, which is carefully cut to reveal the underlying brain. After any hematoma or contusion is removed, the surgeon makes sure that the area is not bleeding. He then closes the dura, replaces the bone, and closes the scalp. (If the brain is very swollen, some surgeons may decide not to replace the bone until the swelling goes down, which may take up to several weeks.) The surgeon 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.

Medical

At the present time, there is no drug or "miracle treatment" that can be given to prevent nerve damage or promote nerve healing after TBI. The best treatment that can be performed in an ICU is to prevent any secondary injury to the brain. The "primary insult" refers to the initial trauma to the brain, whereas a "secondary insult" is any subsequent development that may contribute to neurologic injury. For example, as mentioned above, an injured brain is especially sensitive and vulnerable to decreases in blood pressure that might otherwise be well tolerated. Thus, one way of avoiding secondary insults is to try to maintain the blood pressure at normal or perhaps slightly elevated levels. Likewise, increases in ICP, decreases in blood oxygenation, increases in body temperature, increases in blood glucose, and many other disturbances can potentially worsen neurologic damage. Thus, the prevention of secondary insults is a major part of the ICU management of head-injured patients.

Various monitoring devices may assist the physicians 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 also to drain CSF if the ICP increases. Placement of an oxygen sensor into the jugular vein can detect how much oxygen is in the blood that is coming from the brain and in this way can give an indication of 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 these patients.

Rehabilitation

Once they leave the acute-care hospital, some head-injured patients may benefit from an aggressive rehabilitation program. Such patients usually had less severe initial injuries or have begun to show significant improvement from severe injuries. In some cases, their further recovery may be expedited by transfer to a rehabilitation hospital or to the rehabilitation service of a large hospital. For more severely injured patients or for those whose recovery is slow, constant vigilance is required to prevent the gradual onset of problems with joint mobility, skin integrity, respiratory status, and many other physiologic functions. Patients with moderate or mild injuries, as well as severely injured patients who have improved sufficiently, may be candidates for outpatient therapy.

Regardless of the setting, most head-injury rehabilitation centers emphasize compensatory strategies, which essentially help patients learn to reach the maximum level of function allowed by their impairments. The concept of cognitive retraining, which presumes that at least some of the brain's cognitive capacity can be restored by constant repetition of certain simple tasks, is more controversial but is also emphasized at many centers. Another major goal of head injury rehabilitation is working with patients' families to educate them about what they can realistically expect and how they can best help their injured family member.

Outcome

One of the most widely used systems to classify outcome from head injury is the Glasgow Outcome Scale (Table 2), which is summarized below.

Patients with mild head injury (usually defined as Glasgow Coma Score 13-15) tend to do well. They may sometimes be troubled by headaches, dizziness, irritability, or similar symptoms, but these gradually improve in most cases.

Patients with moderate head injuries fare less well. Approximately 60% will make a good recovery, and another 25% or so will be left with a moderate degree of disability. Death or a persistent vegetative state will be the outcome in roughly 7-10%. The remainder are left with a severe degree of disability.

Not surprisingly, the group comprised of severely head-injured patients has the worst outcomes. Only a quarter to a third of these patients have good outcomes. Moderate disability and severe disability each occur in about a sixth of patients, with moderate disability being slightly more common. Roughly a third of these patients die. The remaining few percent remain persistently vegetative.

The above statistics apply to patients with so-called closed head injuries. For penetrating head injuries, which in modern society are caused most commonly by handguns, outcomes follow a different pattern. Over half of all patients with gunshot wounds to the head who are alive upon arrival at a hospital go on to die 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 (Glasgow Coma Scale score of 13-15). Relatively few patients suffer injuries of intermediate severity (that is, with a Glasgow Coma Scale score of 6-12) from gunshot wounds, but it is this group that has the most variability in outcomes.

It must be emphasized that, despite its usefulness, the Glasgow Outcome Scale is not a good tool with which to measure subtle emotional or cognitive problems. Several months after a severe head injury, patients who have a good score on the Glasgow Outcome Scale may in fact have significant neuropsychological disabilities. Tremendous effort is being directed into finding better ways to evaluate these problems, into improving the quality of prehospital, acute, and rehabilitative care, and into research to learn more about the effects of head injury and their possible treatment.

Table 1: Glasgow Coma Scale
SCALE VALUE	BEST MOTOR RESPONSE	BEST VERBAL RESPONSE	BEST EYE OPENING RESPONSE
6	Obeys commands	--	--
5	Localizes stimulus	Oriented	--
4	Withdraws from stimulus	Conversant, but confused	Eyes open spontaneously
3	Flexes arm	States recognizable words or phrases	Eyes open to voice
2	Extends arm	Makes unintelligible sounds	Eyes open to painful stimulus
1	No response	No response	Remain closed

Table 2: Glasgow Outcome Scale
OUTCOME	SCORE	DESCRIPTION
Good Recovery (GR)	5	Minor disabilities, but able to resume normal life.
Moderate Disability (MD)	4	More significant disabilities, but still able to live independently. Can use public transportation, work in an assisted situation, etc.
Severe Disability (SD)	3	Conscious, but dependent upon others for daily care. Often institutionalized.
Persistent Vegetative State (PVS)	2	Not conscious, though eyes may be open and may "track" movement.
Death (D)	1	Self-explanatory.

Glossary


AXON: The part of a nerve cell that usually sends signals to other nerves or structures.

CONTUSION: A bruise; an area in which blood that has leaked out of blood vessels is mixed with brain tissue.

CSF: Cerebrospinal fluid.

DEPRESSED SKULL FRACTURE: A break in the bones of the head in which some bone is pushed inward, possibly pushing on or cutting into the brain.

DIFFUSE AXONAL INJURY: Damage to the axons of many nerve cells that lie in different parts of the brain.

DIFFUSE BRAIN INJURY: Damage to the brain that can affect many parts of the brain, often in a subtle fashion; examples include diffuse axonal injury and inadequate blood flow.

DURA: Dura mater.

EPIDURAL HEMATOMA: A blood clot between the dura mater and the inside of the skull.

GCS: Glasgow Coma Scale.

GLASGOW COMA SCALE: The most widely used system of classifying the severity of head injuries or other neurologic diseases.

GLASGOW OUTCOME SCALE: A widely used system of classifying outcome after head injury or other neurologic diseases.

INTRACEREBRAL HEMATOMA: A blood clot within the brain.

ICP: Intracranial pressure.

ISCHEMIA: Inadequate blood flow; if prolonged or severe, may lead to a stroke.

LUMBAR DRAIN: A device (usually a long, thin, flexible tube) inserted through the skin into the cerebrospinal fluid space of the lower back; provides a method of draining cerebrospinal fluid.

PUPIL: The black part of the eye through which light enters; enlarges in dim light and decreases in size in bright light.

SUBARACHNOID HEMORRHAGE: Blood in, or bleeding into, the space under the arachnoid membrane, most commonly from trauma or from rupture of an aneurysm.

VENTRICULOSTOMY: An opening into the ventricles of the brain, such as by inserting a small, thin, hollow, flexible catheter.

American Association of Neurological Surgeons / Congress of Neurological Surgeons