Head Injury: End of the road?
Head injury (HI) 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.
The most common cause of HI 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., children and old people. Alcohol or other drug use contributes significantly to the occurrence of many head injuries.
What goes wrong?
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 HI 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. Hematomas that are between the dura and the surface of the brain are called subdural 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, HI 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.
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). 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 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.
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.
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 HI. 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 brain pressure, 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
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. 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.
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.
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