The brain essentially floats within the CSF; as a result, the brain can undergo significant translation and deformation when the head is subjected to significant forces. In a deceleration injury, in which the head impacts a stationary object such as the windshield of a car, the skull stops moving almost instantly. However, the brain continues to move within the skull toward the direction of the impact for a very brief period after the head has stopped moving. This results in significant forces acting on the brain as it undergoes both translation and deformation.

In an acceleration injury, as in a direct blow to the head, the force applied to the skull causes the skull to move away from the applied force. The brain does not move with the skull, and the skull impacts the brain, causing translation and deformation of the brain. The forces that result from either deceleration or acceleration of the brain can cause injury by direct mechanical effects on the various cellular components of the brain or by shear-type forces on axons. In addition to the translational forces, the brain can experience significant rotational forces, which can also lead to shear injuries.

The intracranial compartment is divided into 3 compartments by 2 major dural structures, the falx cerebri and the tentorium cerebelli. The tentorium cerebelli divides the posterior fossa or infratentorial compartment (the cerebellum and the brainstem) from the supratentorial compartment (cerebral hemispheres). The falx cerebri divides the supratentorial compartment into 2 halves and separates the left and right hemispheres of the brain. Both the falx and the tentorium have central openings and prominent edges at the borders of each of these openings. When a significant increase in ICP occurs, caused by either a large mass lesion or significant cerebral edema, the brain can slide through these openings within the falx or the tentorium, a phenomenon known as herniation. As the brain slides over the free dural edges of the tentorium or the falx, it is frequently injured by the dural edge.

Several types of herniation exist, as follows: (1) transtentorial herniation, (2) subfalcine herniation, (3) central herniation, (4) upward herniation, and (5) tonsillar herniation.

Transtentorial herniation occurs when the medial aspect of the temporal lobe (uncus) migrates across the free edge of the tentorium. This causes pressure on the third cranial nerve, interrupting parasympathetic input to the eye and resulting in a dilated pupil. This unilateral dilated pupil is the classic sign of transtentorial herniation and usually (80%) occurs ipsilateral to the side of the transtentorial herniation. In addition to pressure on the third cranial nerve, transtentorial herniation compresses the brainstem.

Subfalcine herniation occurs when the cingulate gyrus on the medial aspect of the frontal lobe is displaced across the midline under the free edge of the falx. This may compromise the blood flow through the anterior cerebral artery complexes, which are located on the medial side of each frontal lobe. Subfalcine herniation does not cause the same brainstem effects as those caused by transtentorial herniation.

Central herniation occurs when a diffuse increase in ICP occurs and each of the cerebral hemispheres is displaced through the tentorium, resulting in significant pressure on the upper brainstem.

Upward, or cerebellar, herniation occurs when either a large mass or increased pressure in the posterior fossa is present and the cerebellum is displaced in an upward direction through the tentorial opening. This also causes significant upper brainstem compression.

Tonsillar herniation occurs when increased pressure develops in the posterior fossa. In this form of herniation, the cerebellar tonsils are displaced in a downward direction through the foramen magnum, causing compression on the lower brainstem and upper cervical spinal cord as they pass through the foramen magnum.

Another aspect of the intracranial anatomy that has a significant role in TBI is the irregular surface of the skull underlying the frontal and temporal lobes. These surfaces contain numerous ridges that can cause injury to the inferior aspect of the frontal lobes and the temporal lobes as the brain glides over these irregular ridges following impact. Typically, these ridges cause cerebral contusions. The roof of the orbit has many ridges, and, as a result, the inferior frontal lobe is one of the most common sites of traumatic cerebral contusions.

Lab Studies:

• After the patient has been stabilized and an appropriate neurologic examination has been conducted, the diagnostic evaluation may begin. Patients with TBI do not require any additional blood tests beyond the standard panel of tests obtained in all trauma patients. A urine toxicology screen and an assessment of the blood alcohol level are important for any patient who has an altered level of consciousness because any central nervous system depressant can impair consciousness.

Imaging Studies:

• Skull radiographs

• Once an important part of the head injury evaluation, skull radiographs have been replaced by CT scans and are rarely used in patients with closed head injury.

• Skull radiographs are occasionally used in the evaluation of penetrating head trauma, and they can help provide a rapid assessment of the degree of foreign body penetration in nonmissile penetrating head injuries (eg, stab wounds).

• Skull radiographs are sometimes used in patients with gunshot wounds to the head to screen for retained intracranial bullet fragments.

• CT scan

• A CT scan is the diagnostic study of choice in the evaluation of TBI because it has a rapid acquisition time, is universally available, is easy to interpret, and is reliable.

• When first introduced more than 25 years ago, CT scans of the brain required almost 30 minutes to complete. This acquisition time has decreased steadily; the current generation of ultrafast CT scanners can perform a head CT scan in less than 1 minute, faster than the time required to enter patient's demographic data into the scanner.

• The standard CT scan for the evaluation of acute head injury is a noncontrast scan that spans from the base of the occiput to the top of the vertex in 5-mm increments.

• Three data sets are obtained from the primary scan, (1) bone windows, (2) tissue windows, and (3) subdural windows. These different types of exposure are necessary because of the significant difference in exposure necessary to visualize various intracranial structures. The bone windows allow for a detailed survey of the bony anatomy of the skull, and the tissue windows allow for a detailed survey of the brain and its contents. The subdural windows provide better visualization of intracranial hemorrhage, especially those hemorrhages adjacent to the brain (eg, subdural hematomas).

• Each intracranial structure has a characteristic density, which is expressed in Hounsfield units. These units are defined according to a scale that ranges from (-) 1000 units to (+) 1000 units. Air is assigned a density of (-) 1000 units, water is assigned a density of 0 units, and bone has a density of (+) 1000 units. On this scale, CSF has a density of (+) 4 to (+) 10 units, white matter has a density of (+) 22 to (+) 36 units, and gray matter has a density of (+) 32 to (+) 46 units. Extravascular blood has a density of (+) 50 to (+) 90 units, and calcified tissue and bone have a density of (+) 800 to (+) 1000 units.

• When reviewing a CT scan, using a systematic approach and following this same protocol each time are important. Consistency is much more important than the specific order used.
  • First, examine the bone windows for fractures, beginning with the cranial vault and then examining the skull base and the facial bones.

  • Next, examine the tissue windows for the presence of (1) extra-axial hematomas (eg, epidural hematomas, subdural hematomas), (2) intraparenchymal hematomas, or (3) contusions.

  • Next, survey the brain for any evidence of pneumocephalus, hydrocephalus, cerebral edema, midline shift, or compression of the subarachnoid cisterns at the base of the brain.

  • Finally, examine the subdural windows for any hemorrhage that may not be visualized easily on the tissue windows.

• Skull fractures may be classified as either linear or comminuted fractures. Linear skull fractures are sometimes difficult to visualize on the individual axial images of a CT scan. The scout film of the CT scan, which is the equivalent of a lateral skull x-ray film, often demonstrates linear fractures. The intracranial sutures are easily mistaken for small linear fractures. However, the sutures have characteristic locations in the skull and have a symmetric suture line on the opposite side. Small diploic veins, which traverse the skull, may also be interpreted as fractures. Comminuted fractures are complex fractures with multiple components. Comminuted fractures may be displaced inwardly; this is defined as a depressed skull fracture.

• Extra-axial hematomas include epidural and subdural hematomas. Epidural hematomas are located between the inner table of the skull and the dura. They are typically biconvex in shape because their outer border follows the inner table of the skull and their inner border is limited by locations at which the dura is firmly adherent to the skull. Epidural hematomas are usually caused by injury to an artery, although 10% of epidural hematomas may be venous in origin. The most common cause of an epidural hematoma is a linear skull fracture that passes through an arterial channel in the bone. The classic example of this is the temporal epidural hematoma caused by a fracture through the course of the middle meningeal artery. Epidural hematomas, especially those of arterial origin, tend to enlarge rapidly.

• Subdural hematomas are located between the dura and the brain. Their outer edge is convex, while their inner border is usually irregularly concave. Subdural hematomas are not limited by the intracranial suture lines; this is an important feature that aids in their differentiation from epidural hematomas. Subdural hematomas are usually venous in origin, although some subdural hematomas are caused by arterial injuries. The classic cause of a posttraumatic subdural hematoma is an injury to one of the bridging veins that travel from the cerebral cortex to the dura. As the brain atrophies over time, the bridging veins become more exposed and, as a result, are more easily injured. Occasionally, the distinction between a subdural and an epidural hematoma can be difficult. The size of an extra-axial hematoma is a more important factor than whether the blood is epidural or subdural in location. In addition, a mixed hematoma with both a subdural and an epidural component is not uncommon.

• Intra-axial hematomas are defined as hemorrhages within the brain parenchyma. These hematomas include intraparenchymal hematomas, intraventricular hemorrhages, and subarachnoid hemorrhages. Subarachnoid hemorrhages that occur because of trauma are typically located over gyri on the convexity of the brain. The subarachnoid hemorrhages that result from a ruptured cerebral aneurysm are usually located in the subarachnoid cisterns at the base of the brain. Cerebral contusions are posttraumatic lesions in the brain that appear as irregular regions, in which high-density changes (ie, blood) and low-density changes (ie, edema) are present. Frequently, 1 of these 2 types of changes predominates within a particular contusion. Contusions are most often caused by the brain gliding over rough surfaces, such as the rough portions of the skull that are present under the frontal and temporal lobes.

• CT scans may be used for classification and for diagnostic purposes. Marshall et al published a classification scheme that classifies head injuries according to the changes demonstrated on CT scan images. This system defines 4 categories of injury, from diffuse injury I to diffuse injury IV.
  • In diffuse injury I, evidence of any significant brain injury is lacking.

  • In diffuse injury II, either no midline shift or a shift of less than 5 mm is present and the CSF cisterns at the base of the brain are widely patent. In addition, no high-density or mixed-density lesions (contusions) of greater than 25 mL in volume are present.

  • In diffuse injury III, a midline shift of less than 5 mm is present, with partial compression or absence of the basal cisterns. No high- or mixed-density lesions with a volume greater than 25 mL are present.

  • Diffuse injury IV is defined as midline shift greater than 5 mm with compression or absence of the basal cisterns and no lesions of high or mixed density greater than 25 mL.

• MRI

• MRI has a limited role in the evaluation of acute head injury. Although MRI provides extraordinary anatomic detail, it is not commonly used to evaluate acute head injuries because of its long acquisition times and the difficulty in obtaining MRIs in persons who are critically ill. However, MRI is used in the subacute setting to evaluate patients with unexplained neurologic deficits.

• MRI is superior to CT scan for helping identify diffuse axonal injury (DAI) and small intraparenchymal contusions. DAI is defined as neuronal injury in the subcortical gray matter or the brainstem as a result of severe rotation or deceleration. DAI is often the reason for a severely depressed level of consciousness in patients who lack evidence of significant injury on CT scan images and have an ICP that is within the reference range.

• Magnetic resonance angiography may be used in some patients with TBI to assess for arterial injury or venous sinus occlusion.

• Angiography

• Once a common diagnostic study in persons with acute head injury, angiography is rarely used in the evaluation of acute head injury today.

• Prior to the development of the CT scan, cerebral angiography provided a reliable means for demonstrating the presence of an intracranial mass lesion.

• Currently, angiography in used in acute head injury only when a vascular injury may be present. This includes patients with unexplained neurologic deficits, especially in the setting of temporal bone fractures, and patients with clinical evidence of a potential carotid injury (eg, hemiparesis, Horner syndrome).

Other Tests:

• Initial evaluation

• The initial evaluation of patients with TBI involves a thorough systemic trauma evaluation according to the advanced trauma life support (ATLS) guidelines. Once this has been completed and the patient is stable from a cardiopulmonary standpoint, attention may be directed to a focused head injury evaluation.

• The evaluation of the spine for potential injury is critically important in patients with TBI because approximately 10% of those with severe head injuries have a concomitant spine injury. Many of these injuries are cervical spine injuries.

• Attempt to obtain a thorough history of the mechanism of the trauma and the events immediately preceding the trauma. Specific information, such as the occurrence of syncope or the onset of a seizure prior to a fall or a motor vehicle accident, prompts a more extended evaluation of the etiology of such an event. Because many patients with TBI have altered levels of consciousness, the history is often provided by family members, police officers, paramedics, or witnesses.

• Neurologic assessment

• After sufficient information has been obtained regarding patient history, appropriate physical and neurologic examinations are performed.

• The neurologic assessment begins with ascertaining the GCS score. This is a screening examination and does not substitute for a thorough neurologic examination.

• In addition to determining the GCS score, the neurologic assessment of patients with TBI should include the following:
  • Brainstem examination - Pupillary examination, ocular movement examination, corneal reflex, gag reflex

  • Motor examination

  • Sensory examination

  • Reflex examination

• Many patients with TBI have significant alterations of consciousness and/or pharmaceuticals present that limit the scope of the neurologic examination. When such factors limit the neurologic examination, noting their presence is important.

• Pupillary examination

• A careful pupillary examination is a critical part of the evaluation of patients with TBI, especially in patients with severe injuries. When muscle relaxants have been administered to a patient, the only aspect of the neurologic examination that may be evaluated is the pupillary examination.

• Several factors can alter the pupillary examination results. Narcotics cause pupillary constriction (meiosis), and medications or drugs that have sympathomimetic properties cause pupillary dilation (mydriasis). These effects are often strong enough to blunt or practically eliminate pupillary responses. Prior eye surgery, such as cataract surgery, can also alter or eliminate pupillary reactivity.

• Proper assessment of the pupillary response requires the use of a strong light source to override any of the potential factors that may affect pupillary reaction. Each pupil must be assessed individually, with at least 10 seconds between assessment of each eye to allow consensual responses to fade prior to stimulating the opposite eye.

• A normal pupillary examination result consists of bilaterally reactive pupils that react to both direct and consensual stimuli. Bilateral small pupils can be caused by narcotics, pontine injury (due to disruption of sympathetic centers in the pons), or early central herniation (mass effect on the pons).

• Bilateral fixed and dilated pupils are secondary to inadequate cerebral perfusion. This can result from diffuse cerebral hypoxia or severe elevations of ICP preventing adequate blood flow into the brain.

• Pupils that are fixed and dilated usually indicate an irreversible injury. If due to systemic hypoxia, the pupils sometimes recover reactivity when adequate oxygenation is restored.

• A unilateral fixed (unresponsive) and dilated pupil has many potential causes. A pupil that does not constrict when light is directed at the pupil but constricts when light is directed into the contralateral pupil (intact consensual response) is indicative of a traumatic optic nerve injury.

• A unilateral dilated pupil that does not respond to either direct or consensual stimulation usually indicates transtentorial herniation.

• Unilateral constriction of a pupil is usually secondary to Horner syndrome, in which the sympathetic input to the eye is disrupted and the pupil constricts due to more parasympathetic than sympathetic stimulation. In patients with TBI, Horner syndrome may be caused by an injury to the sympathetic chain at the apex of the lung or a carotid artery injury. A unilateral constricted pupil can be caused by a unilateral brainstem injury, but this is quite rare.

• A core optic pupil is a pupil that appears irregular in shape. This is caused by a lack of coordination of contraction of the muscle fibers of the iris and is associated with midbrain injuries.

• Ocular movement examination

• When the patient's level of consciousness is altered significantly, a loss of voluntary eye movements often occurs and abnormalities in ocular movements are frequently present. These abnormalities can provide specific clues to the extent and location of injury.

• Ocular movements involve the coordination of multiple centers in the brain, including the frontal eye fields, the paramedian pontine reticular formation (PPRF), the medial longitudinal fasciculus (MLF), and the nuclei of the third and sixth cranial nerves. In patients in whom voluntary eye movements cannot be assessed, oculocephalic and oculovestibular testing may be performed.

• Oculocephalic testing

• Oculocephalic testing (doll's eyes) involves observation of eye movements when the head is turned from side to side. This maneuver helps assess the integrity of the horizontal gaze centers.

• Before performing oculocephalic testing, the status of the cervical spine must be established. If a cervical spine injury has not been excluded reliably, oculocephalic testing should not be performed.

• When assessing oculocephalic movements, the head is elevated to 30° from horizontal and is rotated briskly from side to side.

• A normal response is for the eyes to turn away from the direction of the movement as if they are fixating on a target that is straight ahead. This is similar to the way a doll's eyes move when the head is turned; this is the origin of the term doll's eyes.

• If the eyes remain fixed in position and do not rotate with the head, this is indicative of dysfunction in the lateral gaze centers and is referred to as negative doll's eyes. Some patients may have negative doll's eyes and normal oculovestibular reflexes.

• Oculovestibular testing

• Oculovestibular testing, also known as cold calorics, is another method for assessment of the integrity of the gaze centers. Oculovestibular testing is performed with the head elevated to 30° from horizontal to bring the horizontal semicircular canal into the vertical position.

• Oculovestibular testing requires the presence of an intact tympanic membrane; this must be assessed before beginning the test.

• In oculovestibular testing, 20 mL of ice-cold water is instilled slowly into the auditory canal. If is no response occurs within 60 seconds, the test is repeated with 40 mL of cold water.

• When cold water is irrigated into the external auditory canal, the temperature of the endolymph falls and the fluid begins to settle. This causes an imbalance in the vestibular signals and initiates a compensatory response.

• Cold-water irrigation in the ear of an alert patient results in a fast nystagmus away from the irrigated ear and a slow compensatory nystagmus toward the irrigated side. If warm water is used, the opposite will occur; the fast component of nystagmus will be toward the irrigated side, and the slow component will be away from the irrigated side. This is the basis for the acronym COWS, which stands for cold opposite, warm same. This refers to the direction of the fast component of nystagmus.

• As the level of consciousness declines, the fast component of nystagmus fades gradually. Thus, in unconscious patients, only the slow phase of nystagmus may be evaluated.

• A normal oculocephalic response to cold-water calorics (ie, eye deviation toward the side of irrigation) indicates that the injury spares the PPRF, the MLF, and third and sixth cranial nerve nuclei. This means that the level of injury must be rostral to the reticular activating system in the upper brainstem.

• If a unilateral frontal lobe injury is present, the eyes are deviated toward the side of injury prior to caloric testing. Cold-water irrigation of the opposite ear results in a normal response to caloric testing (ie, eye deviation toward the irrigated side) because the injury is in the frontal region and spares the pontine gaze centers.

• When a pontine injury is present, the eyes often deviate away from the side of injury. In this situation, cold-water irrigation of the contralateral ear does not cause the gaze to deviate toward the irrigated ear because an injury has occurred at the level of the pons and the pontine gaze centers are compromised.

• A dysconjugate response to caloric testing suggests an injury to either the third or sixth cranial nerves or an injury to the MLF, resulting in an internuclear ophthalmoplegia.

• If caloric testing causes a skew deviation, in which the eyes are dysconjugate in the vertical direction, this indicates a lesion in the brainstem. The exact location of injury that results in skew deviation is not known.

• Motor examination

• After completing the brainstem examination, a motor examination should be performed. A thorough motor or sensory examination is difficult to perform in any patient with an altered level of consciousness.

• When a patient is not alert enough to cooperate with strength testing, the motor examination is limited to an assessment of asymmetry in the motor examination findings. This may be demonstrated by an asymmetric response to central pain stimulation or a difference in muscle tone between the left and right sides. A finding of significant asymmetry during the motor examination may be indicative of a hemispheric injury and raises the possibility of a mass lesion.

• Sensory examination

• Performing a useful sensory examination in patients with TBI is often difficult.

• Patients with altered levels of consciousness are unable to cooperate with sensory testing, and findings from a sensory examination are not reliable in patients who are intoxicated or comatose.

• Peripheral reflex examination

• A peripheral reflex examination can be useful to help identify gross asymmetry in the neurologic examination.

• This may indicate the presence of a hemispheric mass lesion.

Closed head injury

Mild head injury

Most head injuries are mild head injuries. Most people presenting with mild head injuries will not have any progression of their head injury; however, up to 3% of mild head injuries progress to more serious injuries. Mild head injuries may be separated into low-risk and moderate-risk groups. Patients with mild-to-moderate headaches, dizziness, and nausea are considered to have low-risk injuries. Many of these patients require only minimal observation after they are assessed carefully, and many do not require radiographic evaluation. These patients may be discharged if a reliable individual can monitor them.

Patients who are discharged after mild head injury should be given an instruction sheet for head injury care. The sheet should explain that the person with the head injury should be awakened every 2 hours and assessed neurologically. Caregivers should be instructed to seek medical attention if patients develop severe headaches, persistent nausea and vomiting, seizures, confusion or unusual behavior, or watery discharge from either the nose or the ear.

Patients with mild head injuries typically have concussions. A concussion is defined as physiologic injury to the brain without any evidence of structural alteration. Concussions are graded on a scale of I-V. A grade I concussion is one in which a person is confused temporarily but does not display any memory changes. In a grade II concussion, brief disorientation and anterograde amnesia of less than 5 minutes' duration are present. In a grade III concussion, retrograde amnesia and loss of consciousness for less than 5 minutes are present, in addition to the 2 criteria for a grade II concussion. Grade IV and grade V concussions are similar to a grade III, except that in a grade IV concussion, the duration of loss of consciousness is 5-10 minutes, and in a grade V concussion, the loss of consciousness is longer than 10 minutes.

As many as 30% of patients who experience a concussion develop postconcussive syndrome (PCS). PCS consists of a persistence of any combination of the following after a head injury: headache, nausea, emesis, memory loss, dizziness, diplopia, blurred vision, emotional lability, or sleep disturbances. Fixed neurologic deficits are not part of PCS, and any patient with a fixed deficit requires careful evaluation. PCS usually lasts 2-4 months. Typically, the symptoms peak 4-6 weeks following the injury. On occasion, the symptoms of PCS last for a year or longer. Approximately 20% of adults with PCS will not have returned to full-time work 1 year after the initial injury, and some are disabled permanently by PCS. PCS tends to be more severe in children than in adults. When PCS is severe or persistent, a multidisciplinary approach to treatment may be necessary. This includes social services, mental health services, occupational therapy, and pharmaceutical therapy.

After a mild head injury, those displaying persistent emesis, severe headache, anterograde amnesia, loss of consciousness, or signs of intoxication by drugs or alcohol are considered to have a moderate-risk head injury. These patients should be evaluated with a head CT scan. Patients with moderate-risk mild head injuries can be discharged if their CT scan findings reveal no pathology, their intoxication is cleared, and they have been observed for at least 8 hours.

Moderate and severe head injury

The treatment of moderate and severe head injuries begins with initial cardiopulmonary stabilization by ATLS guidelines. The initial resuscitation of a patient with a head injury is of critical importance to prevent hypoxia and hypotension. In the Traumatic Coma Data Bank study, patients with head injury who presented to the hospital with hypotension had twice the mortality rate of patients who did not present with hypotension. The combination of hypoxia and hypotension resulted in a mortality rate 2.5 times greater than if neither of these factors was present.

Once a patient has been stabilized from the cardiopulmonary standpoint, evaluation of their neurologic status may begin. The initial GCS score provides a classification system for patients with head injuries but does not substitute for a neurologic examination. After assessment of the coma score, a neurologic examination should be performed. If a patient has received muscle relaxants, the only neurologic response that may be evaluated is the pupillary response.

After a thorough neurologic assessment has been performed, a CT scan of the head is obtained. The results of the CT scan help determine the next step. If a surgical lesion is present, arrangements are made for immediate transport to the operating room. Fewer than 10% of patients with TBI have an initial surgical lesion.

Although no strict guidelines exist for defining surgical lesions in persons with head injury, most neurosurgeons consider any of the following to represent indications for surgery in patients with head injuries: extra-axial hematoma with midline shift greater than 5 mm, intra-axial hematoma with volume greater than 30 mL, an open skull fracture, or a depressed skull fracture with more than 1 cm of inward displacement. In addition, any temporal or cerebellar hematoma that is larger than 3 cm in diameter is considered a high-risk hematoma because these regions of the brain are smaller and do not tolerate additional mass as well as the frontal, parietal, and occipital lobes. These high-risk temporal and cerebellar hematomas are usually evacuated immediately

If no surgical lesion is present on the CT scan image, or following surgery if one is present, treatment of the head injury begins. The first phase of treatment is to institute general measures. Once appropriate fluid resuscitation has been completed and the volume status is determined to be normal, intravenous fluids are administered to maintain the patient in a state of euvolemia or mild hypervolemia. A previous tenet of head injury treatment was fluid restriction, which was believed to limit the development of cerebral edema and increased ICP. Fluid restriction decreases intravascular volume and, therefore, decreases cardiac output. A decrease in cardiac output often results in decreased cerebral flow, which results in decreased brain perfusion and may cause an increase in cerebral edema and ICP. Thus, fluid restriction is contraindicated in patients with TBI.

Another supportive measure used to treat patients with head injuries is elevation of the head. When the head of the bed is elevated to 20-30°, the venous outflow from the brain is improved, thus helping to reduce ICP. If a patient is hypovolemic, elevation of the head may cause a drop in cardiac output and CBF; therefore, the head of the bed is not elevated in hypovolemic patients. In addition, the head should not be elevated (1) in patients in whom a spine injury is a possibility or (2) until an unstable spine has been stabilized.

Sedation is often necessary in patients with traumatic injury. Some patients with moderate head injuries have significant agitation and require sedation. In addition, patients with multisystem trauma often have painful systemic injuries that require pain medication, and many intubated patients require sedation. Short-acting sedatives and analgesics should be used to accomplish proper sedation without eliminating the ability to perform periodic neurologic assessments. This requires careful titration of medication doses and periodic weaning or withholding of sedation to allow periodic neurologic assessment.

The use of anticonvulsants in patients with TBI is a controversial issue. No evidence exists that the use of anticonvulsants decreases the incidence of late-onset seizures in patients with either closed head injury or TBI. Temkin et al demonstrated that the routine use of Dilantin in the first week following TBI decreases the incidence of early-onset (within 7 d of injury) seizures but does not change the incidence of late-onset seizures. In addition, the prevention of early posttraumatic seizures does not improve the outcome following TBI. Therefore, the prophylactic use of anticonvulsants is not recommended for more than 7 days following TBI and is considered optional in the first week following TBI.

After instituting general supportive measures, the issue of ICP monitoring is addressed. ICP monitoring has consistently been shown to improve outcome in patients with head injuries. ICP monitoring is indicated for any patient with a GCS score less than 9, any patient with a head injury who requires prolonged deep sedation or pharmacologic relaxants for a systemic condition, or any patient with an acute head injury who is undergoing extended general anesthesia for a nonneurosurgical procedure.

ICP monitoring involves placement of an invasive probe to measure the ICP. Unfortunately, noninvasive means of monitoring ICP do not exist, although they are under development. ICP may be monitored by means of an intraparenchymal monitor, an intraventricular monitor (ventriculostomy), or an epidural monitor. These devices measure ICP by fluid manometry, strain-gauge technology, or fiberoptic technology.

Intraparenchymal ICP monitors are devices that are placed into the brain parenchyma to measure ICP by means of fiberoptic, strain-gauge, or other technologies. The intraparenchymal monitors are very accurate; however, they do not allow for drainage of CSF. Epidural devices measure ICP via a strain-gauge device placed through the skull into the epidural space. This is an older form of ICP measurement and is rarely used today because the other technologies available are more accurate and more reliable.

A ventriculostomy is a catheter placed through a small twist drill hole into the lateral ventricle. The ICP is measured by transducing the pressure in a fluid column. Ventriculostomies allow for drainage of CSF, which can be effective in decreasing the ICP.

Once an ICP monitor has been placed, ICP is monitored continuously. No absolute value of ICP exists for which treatment is implemented automatically. In adults, the reference range of ICP is 0-15 mm Hg. The normal ICP waveform is a triphasic wave, in which the first peak is the largest peak and the second and third peaks are progressively smaller. When intracranial compliance is abnormal, the second and third peaks are usually larger than the first peak. In addition, when intracranial compliance is abnormal and ICP is elevated, pathologic waves may appear.

Lundberg described 3 types of abnormal ICP waves, A, B, and C waves. Lundberg A waves, known as plateau waves, have a duration of 5-20 minutes and an amplitude of 50 mm Hg over the baseline ICP. After an episode of A waves dissipates, the ICP is reset to a baseline level that is higher than when the waves began. Lundberg A waves are a sign of severely compromised intracranial compliance. The rapid increase in ICP caused by these waves can result in a significant decrease in CPP and may lead to herniation.

Lundberg B waves have a duration of less than 2 minutes, and they have an amplitude of 10-20 mm Hg above the baseline ICP. B waves are also related to abnormal intracranial compliance. Because of their smaller amplitude and shorter duration, B waves are not as deleterious as A waves.

C waves, known as Hering-Traube waves, are low-amplitude waves that may be superimposed on other waves. They may be related to increased ICP; however, C waves can also occur in the setting of normal ICP and compliance.

When treating elevated ICP, remember that the goal of treatment is to optimize conditions within the brain to prevent secondary injury and to allow the brain to recover from the initial insult. Maintaining ICP within the reference range is part of an approach designed to optimize both CBF and the metabolic state of the brain. Treatment of elevated ICP is a complex process that should be tailored to each particular patient's situation and should not be approached in a “cookbook” manner. Many potential interventions are used to lower ICP, and each of these is designed to improve intracranial compliance, which results in improved CBF and decreased ICP.

The Monro-Kellie doctrine provides the framework for understanding and organizing the various treatments for elevated ICP. In patients with head injuries, the total intracranial volume is composed of the total volume of the brain, the CSF, intravascular blood volume, and any intracranial mass lesions. The volume of one of these components must be reduced to improve intracranial compliance and to decrease ICP. The discussion of the different treatments for elevated ICP is organized according to which component of intracranial volume they affect.

The first component of total intracranial volume to consider is the blood component. This includes all intravascular blood, both venous and arterial, and comprises approximately 10% of total intracranial volume. Elevation of the head increases venous outflow and decreases the volume of venous blood within the brain. This results in a small improvement in intracranial compliance and, therefore, has only a modest effect on ICP.

The second component of intracranial vascular volume is the arterial blood volume. This may be reduced by mild-to-moderate hyperventilation, in which the PCO₂ is reduced to 30-35 mm Hg. This decrease in PCO₂ causes vasoconstriction at the level of the arteriole, which decreases blood volume enough to reduce ICP. The effects of hyperventilation have a duration of action of approximately 48-72 hours, at which point the brain resets to the reduced level of PCO₂. This is an important point because once hyperventilation is used, the PCO₂ should not be returned to normal rapidly. This may cause rebound vasodilatation, which can result in increased ICP.

At one time, severe hyperventilation was an important component of the treatment of increased ICP. Reducing PCO₂ to less than 25 mm Hg has been shown to cause enough vasoconstriction that CBF is reduced to the point at which a high probability exists of developing cerebral ischemia. Therefore, prolonged severe hyperventilation is not used routinely to treat elevated ICP. Brief periods of severe hyperventilation may be used to treat patients with transient ICP elevations due to pressure waves or in the initial treatment of patients in neurologic distress until other measures can be instituted.

CSF represents the next component of total intracranial volume and accounts for 2-3% of total intracranial volume. In adults, total CSF production is approximately 20 mL/h or 500 mL/d. In many patients with TBI who have elevated ICP, a ventriculostomy may be placed and CSF may be drained. Removal of small amounts of CSF hourly can result in improvements in compliance that result in significant improvements in ICP.

The third and largest component of total intracranial volume is the brain or tissue component, which comprises 85-90% of the total intracranial volume. When significant brain edema is present, it causes an increase in the tissue component of the total intracranial volume and results in decreased compliance and increased ICP. Treatments for elevated ICP that reduce total brain volume include diuretics, perfusion augmentation (CPP strategies), metabolic suppression, and decompressive procedures.

Diuretics are powerful in their ability to decrease brain volume and, therefore, decrease ICP. Mannitol, an osmotic diuretic, is the most common diuretic used. Mannitol is a sugar alcohol that draws water out from the brain into the intravascular compartment. It has a rapid onset of action and a duration of action of 2-8 hours. Mannitol is usually administered as a bolus because it is much more effective when given in intermittent boluses than when used as a continuous infusion. The standard dose ranges from 0.25-1 g/kg, administered every 4-6 hours. Because mannitol causes significant diuresis, electrolytes and serum osmolality must be monitored carefully during its use. In addition, careful attention must be given to providing sufficient hydration to maintain euvolemia. The limit for mannitol is 4 g/kg/d. At daily doses higher than this, mannitol can cause renal toxicity. Mannitol should not be given if the patient's serum sodium level is greater than 145 or serum osmolality is greater than 315 mOsm.

Other diuretics that sometimes are used in patients with TBI include furosemide, glycerol, and urea. Mannitol is preferred over furosemide because it tends to cause less severe electrolyte imbalances than a loop diuretic. Interestingly, mannitol and furosemide have a synergistic effect when combined; however, this combination tends to cause severe electrolyte disturbances. Urea and glycerol have also been used as osmotic diuretics. Both of these compounds are smaller molecules than mannitol and, as a result, tend to equilibrate within the brain sooner than mannitol; therefore, they have a shorter duration of action than mannitol. Urea has the additional problem that it can cause severe skin sloughing if it infiltrates into the skin.

CPP management involves artificially elevating the blood pressure to increase the MAP and the CPP. Because autoregulation is impaired in the injured brain, pressure-passive CBF develops within these injured areas. As a result, these injured areas of the brain often have insufficient blood flow, and tissue acidosis and lactate accumulation occur. This causes vasodilation, which increases cerebral edema and ICP. When the CPP is raised to greater than 65-70 mm Hg, the ICP is often lowered because increased blood flow to injured areas of the brain decreases the tissue acidosis. This often results in a significant decrease in ICP.

Metabolic therapies are designed to decrease the cerebral metabolic rate, which decreases ICP. Metabolic therapies are powerful means of reducing ICP, but they are reserved for situations in which other therapies have failed to control ICP. This is because metabolic therapies have diffuse systemic effects and often result in severe adverse effects, including hypotension, immunosuppression, coagulopathies, arrhythmias, and myocardial suppression. Metabolic suppression may be achieved through drug therapies or induced hypothermia.

Barbiturates are the most common class of drugs used to suppress cerebral metabolism. Barbiturate coma is typically induced with pentobarbital. A loading dose of 10 mg/kg is administered over 30 minutes, and then 5 mg/kg/h is administered for 3 hours. A maintenance infusion of 1-2 mg/kg/h is begun after loading is completed. The infusion is titrated to provide burst suppression on continuous electroencephalogram monitoring and a serum level of 3-4 mg/dL. Typically, the barbiturate infusion is continued for 48 hours, and then the patient is weaned off the barbiturates. If the ICP again escapes control, the patient may be reloaded with pentobarbital and weaned again in several days.

Hypothermia may also be used to suppress cerebral metabolism. The use of mild hypothermia involves decreasing the core temperature to 34-35°C for 24-48 hours and then slowly rewarming the patient over 2-3 days. Patients with hypothermia are also at risk for hypotension and systemic infections.

Another treatment that may be used in patients with TBI with refractory ICP elevation is decompressive craniectomy. In this surgical procedure, a large section of the skull is removed and the dura is expanded. This increases the total intracranial volume and, therefore, decreases ICP. Which patients benefit from decompressive craniectomy has not been established. Some believe that patients with refractory ICP elevation who have diffuse injury but do not have significant contusions or infarctions will benefit from decompressive craniectomy.

Management of elevated ICP involves using a combination of treatments. Each patient represents a slightly different set of circumstances, and treatment must be tailored to each patient. Although no rigid protocols have been established for the treatment of head injury, many published algorithms provide treatment schemas.

The American Association of Neurologic Surgeons published a comprehensive evidence-based review of the treatment of TBI, called the "Guidelines for the Management of Severe Head Injury." In these guidelines, 3 different categories of treatments, standards, guidelines, and options are outlined. Standards are the accepted principles of management that reflect a high degree of clinical certainty. Guidelines are a particular strategy or a range of management options that reflect a high degree of clinical certainty. Options are strategies for patient management for which clinical certainty is unclear.

Penetrating trauma

The treatment of penetrating brain injuries involves 2 main aspects. The first is the treatment of the TBI caused by a penetrating object. Penetrating brain injuries, especially from high-velocity missiles, frequently result in severe ICP elevations. This aspect of penetrating brain injury treatment is identical to the treatment of closed head injuries.

The second aspect of penetrating head injury treatment involves debridement and removal of the penetrating objects. Penetrating injuries require careful debridement because these wounds are frequently dirty. When objects penetrate the brain, they introduce pathogens into the brain from the scalp surface and from the surface of the penetrating object.

Penetrating injuries may be caused by high-velocity missiles (eg, bullets), penetrating objects (eg, knives, tools), or fragments of bone driven into the brain. Bullet wounds are treated with debridement of as much of the bullet tract as possible, dural closure, and reconstruction of the skull as needed. If the bullet can be removed without significant risk of neurologic injury, it should be removed to decrease the risk of subsequent infection. Penetrating objects such as knives require removal to prevent further injury and infection. If the penetrating object either is near or traverses a major vascular structure, an angiogram is necessary to assess for potential vascular injury. When the risk of vascular injury is present, penetrating objects should be removed only after appropriate access has been obtained to ensure that vascular control is easily achieved.

Penetrating brain injuries are associated with a high rate of infection, both early infections and delayed abscesses. Appropriate debridement and irrigation of wounds helps to decrease the infection rate. Some of the risk factors for infection following penetrating brain injury include extensive bony destruction, persistent CSF leak, and an injury pathway that violates an air sinus.

Late-onset epilepsy is a common consequence of penetrating brain injuries and can occur in up to 50% of patients with penetrating brain injuries. No evidence exists that prophylactic anticonvulsants decrease the development of late-onset epilepsy. During the Vietnam War, prophylactic anticonvulsants were used, and the rate of late-onset epilepsy was not different from that of previous wars, when prophylactic anticonvulsants were not used.

Head injury in children

Head injuries in children differ from head injuries in adults in several ways. Children tend to have more diffuse injuries than adults, and traumatic intracerebral hematomas are less common in children than in adults. In addition, early posttraumatic seizures are more common in children than in adults. Overall, children have much lower morbidity and mortality rates from traumatic head injury compared to adults.

When a child with a head injury is being evaluated, nonaccidental trauma must be excluded. In the United States, as many as 1 million cases of nonaccidental trauma in children may occur annually. TBI is the most common cause of morbidity and mortality in nonaccidental trauma in children.

Radiographic signs of nonaccidental trauma include unexplained multiple or bilateral skull fractures, subdural hematomas of different ages, cortical contusions and shearing injures, cerebral ischemia, and retinal hemorrhages. If any of these are present, the case should be referred to the proper child welfare agency.

Follow-up care: For excellent patient education resources, visit eMedicine's Back, Ribs, Neck, and Head Center, Back, Neck, and Head Injury Center, and Eye and Vision Center. Also, see eMedicine's patient education articles Concussion, Bicycle and Motorcycle Helmets, and Black Eye.