AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Traumatic brain injury (TBI) continues to be an enormous public health problem, even with modern medicine in the 21st century. Most patients with TBI (75-80%) have mild head injuries; the remaining injuries are divided equally between moderate and severe categories.

The cost to society of TBI is staggering, from both an economic and an emotional standpoint. Almost 100% of persons with severe head injury and as many as two thirds of those with moderate head injury will be permanently disabled in some fashion and will not return to their premorbid level of function. In the United States, the direct cost of care for patients with TBI, excluding inpatient care, is estimated at more than $25 billion annually. The impact is even greater when one considers that most severe head injuries occur in adolescents and young adults.

See related CME at Severe Traumatic Brain Injury: Evolution and Current Surgical Management.

Frequency

The annual incidence of TBI in the United States has been estimated to be 180-220 cases per 100,000 population. In the United States, with a population of almost 300 million, approximately 600,000 new TBIs occur per year. As many as 10% of these injuries are fatal, resulting in almost 550,000 persons hospitalized annually in the United States with head injuries.

Etiology

While various mechanisms may cause TBI, the most common causes include motor vehicle accidents (eg, collisions between vehicles, pedestrians struck by motor vehicles, bicycle accidents), falls, assaults, sports-related injuries, and penetrating trauma.

Motor vehicle accidents account for almost half of the TBIs in the United States, and in suburban/rural settings, they account for most TBIs. In cities with populations greater than 100,000, assaults, falls, and penetrating trauma are more common etiologies of head injury.

The male-to-female ratio for TBI is nearly 2:1, and TBI is much more common in persons younger than 35 years.

Motorcycle-related head injury

Motorcycle-related head injuries deserve special mention. Motorcycle rights organizations dedicated to promoting safety and to preserving individual freedom suggest that safety should be a choice rather than a requirement; safety is a good choice, but individual motorcyclists should have the right to make a bad choice that ends in disaster if they so choose. A hallmark of the antihelmet movement is the argument that motorcyclists who do not wear helmets can perceive (ie, see and hear) their environment more effectively and, thus, can avoid impending accidents by anticipating them earlier. This argument is fallacious. 

Most accidents involving adult, otherwise responsible, motorcyclists are caused by moving objects hitting motorcyclists or by motorcyclists hitting a stationary object after being forced into an unusual position in an attempt to avoid something in their path. A full-face helmet restricts a relatively small portion of inconsequential downward and lateral peripheral vision. Similarly, it is highly improbable that a motorcyclist will hear an impending accident. A marginal increase in the ability to hear road noise and to see downward and laterally is not an improvement in the ability to avoid most accidents. 

The medical literature regarding motorcyclists’ head injury is clear.  Head trauma is a devastating injury for motorcyclists and their families, and rehabilitation for survivors is prolonged and expensive. Injury expenses for motorcyclists who do not wear helmets far exceed that of motorcyclists who wear helmets. More importantly, the burden of caring for a motorcyclist with a head injury is frequently borne by the taxpayers, regardless of the insurance status of the injured motorcyclist.

Pathophysiology

Appropriate management of TBI requires an understanding of the pathophysiology of head injury. In addition to the obvious functional differences, the brain has several features that distinguish it from other organ systems. The most important of these differences is that the brain is contained within the skull, a rigid and inelastic container. Because the brain is housed within this inelastic container, only small increases in volume within the intracranial compartment can be tolerated before pressure within the compartment rises dramatically. This concept is defined by the Monro-Kellie doctrine, which states that the total intracranial volume is fixed because of the inelastic nature of the skull. The intracranial volume (V i/c) is equal to the sum of its components, as follows:

V i/c = V (brain) + V (cerebrospinal fluid) + V (blood)

In the typical adult, the intracranial volume is approximately 1500 mL, of which the brain accounts for 85-90%, intravascular cerebral blood volume accounts for 10%, and cerebrospinal fluid (CSF) accounts for the remainder (<3%). When a significant head injury occurs, cerebral edema often develops, which increases the relative volume of the brain. Because the intracranial volume is fixed, the pressure within this compartment rises unless some compensatory action occurs, such as a decrease in the volume of one of the other intracranial components. This is intimately related to the concept of intracranial compliance, which is defined as the change in pressure due to changes in volume.

Compliance = Change in volume / change in pressure

Compliance is based on the pressure volume index (PVI) within the intracranial compartment. The PVI describes the change in intracranial pressure (ICP) that occurs when a small amount of fluid is added to or withdrawn from the intracranial compartment. Simply stated, the brain has very limited compliance and cannot tolerate significant increases in volume that can result from diffuse cerebral edema or from significant mass lesions, such as a hematoma. The rationale for each treatment of head injury is based on the concept of the Monro-Kellie doctrine and how a particular intervention affects the intracranial compliance. When the volume of any of the components of the total intracranial volume is decreased, the ICP may be decreased.

A second crucial concept in TBI pathophysiology is the concept of cerebral perfusion pressure (CPP). CPP is defined as the difference between the mean arterial pressure (MAP) and the ICP.

CPP = MAP - ICP

In practical terms, CPP is the net pressure of blood delivery to the brain. In the noninjured brain in individuals without long-standing hypertension, cerebral blood flow (CBF) is constant in the range of MAPs of 50-150 mm Hg. This is due to autoregulation by the arterioles, which will constrict or dilate within a specific range of blood pressure to maintain a constant amount of blood flow to the brain.

When the MAP is less than 50 mm Hg or greater than 150 mm Hg, the arterioles are unable to autoregulate and blood flow becomes entirely dependent on the blood pressure, a situation defined as pressure-passive flow. The CBF is no longer constant but is dependent on and proportional to the CPP. Thus, when the MAP falls below 50 mm Hg, the brain is at risk of ischemia due to insufficient blood flow, while a MAP greater than 160 mm Hg causes excess CBF that may result in increased ICP. While autoregulation works well in the noninjured brain, it is impaired in the injured brain. As a result, pressure-passive flow occurs within and around injured areas and, perhaps, globally in the injured brain.

TBI may be divided into 2 categories, primary brain injury and secondary brain injury. Primary brain injury is defined as the initial injury to the brain as a direct result of the trauma. This is the initial structural injury caused by the impact on the brain, and, like other forms of neural injury, patients recover poorly. Secondary brain injury is defined as any subsequent injury to the brain after the initial insult. Secondary brain injury can result from systemic hypotension, hypoxia, elevated ICP, or as the biochemical result of a series of physiologic changes initiated by the original trauma. The treatment of head injury is directed at either preventing or minimizing secondary brain injury.

Elevated ICP may result from the initial brain trauma or from secondary injury to the brain. In adults, normal ICP is considered 0-15 mm Hg. In young children, the upper limit of normal ICP is lower, and this limit may be considered 10 mm Hg. Elevations in ICP are deleterious because they can result in decreased CPP and decreased CBF, which, if severe enough, may result in cerebral ischemia. Severe elevations of ICP are dangerous because, in addition to creating a significant risk for ischemia, uncontrolled ICP may cause herniation. Herniation involves the movement of the brain across fixed dural structures, resulting in irreversible and often fatal cerebral injury.

Clinical

TBI may be divided into 2 broad categories, closed head injury and penetrating head injury. This is not purely a mechanistic division because some aspects of the treatment of these 2 types of TBIs differ. The clinical presentation of the patient with TBI varies significantly, from an ambulatory patient complaining of a sports-related head injury to the moribund patient arriving via helicopter following a high-speed motor vehicle accident.

The Glasgow Coma Scale (GCS) developed by Jennett and Teasdale is used to describe the general level of consciousness of patients with TBI and to define broad categories of head injury.¹ The GCS is divided into 3 categories, eye opening (E), motor response (M), and verbal response (V). The score is determined by the sum of the score in each of the 3 categories, with a maximum score of 15 and a minimum score of 3, as follows:

GCS score = E + M + V

Glasgow Coma Scale

INDICATIONS

Section 3 of 10  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Traumatic injury and brain failure

As a type of organ system failure, brain failure invariably affects consciousness. Consciousness is structurally produced in the cerebral hemispheres, including the pons and the medulla. These structures are all interconnected by the reticular formation, which begins in the medulla and extends to the midbrain, where it forms the reticular activating system. This pathway modulates the perception of events and controls integrated responses.

Clinical evaluation of consciousness states is heavily dependent on the findings from the physical examination. When the physical examination yields visual and palpable clues to the integrity of consciousness, impairment thereof may be classified into one of the following categories: 

• Cloudy consciousness: This state is defined as a mild deficit in the speed of information processing by the brain. This results from macrotearing and histological-level disruption of cell-to-cell connectivity occurring throughout the brain disrupting physical connectivity between brain regions, exacerbated by vascular compromise of a mechanical and/or biochemical nature causing islands of nonfunctional or impaired tissue in the brain parenchyma. Cloudy consciousness may be noted after mild-to-moderate head trauma and may persist for several months. Memory of recent events is often diminished, but long-term memory typically remains intact.
• Lethargy: This state is defined as a decrease in alertness, resulting in impaired ability to perform tasks that are normally accomplished without effort. Patients rouse briefly in response to stimuli and then settle back into inactivity when left alone. They retain awareness of their immediate environment.
• Obtundation: This state is defined as a decrease in awareness and alertness, in which patients rouse briefly in response to stimuli and follow simple commands but are unaware of their immediate surroundings. When stimulation ceases, they settle back into inactivity.
• Stupor: In this state, patients cannot communicate clearly but can be aroused by continued painful stimulation. Arousal may be manifested only as withdrawal from painful stimuli. As soon as stimuli are removed, the patient settles back into inactivity.
• Coma: In this state, patients do not respond to even the most vigorous stimuli.
• Brain death: This state is equivalent to functional decapitation and is characterized by irreversible cessation of whole-brain function and hemisphere and brainstem function.

The efficacy of the physical examination in the evaluation of consciousness diminishes when visual clues disappear (eg, during heavy sedation, therapeutic musculoskeletal paralysis). In such situations, monitoring of cerebral function by compressed spectral array is helpful in assessing the effect of therapy on neuronal function. 

• S - SYMMETRY - Compare the pattern of asymmetrical patterns. Can indicate diminished perfusion to one hemisphere, cerebral embolism, or thrombosis.
• A - AMPLITUDE - Compare the altitude of the vectors. Asymmetric hemispherical amplitude suggests agitation under paralysis. Low amplitude suggests sedation and quiescence.
• F - FREQUENCY - Compare the distribution of vectors throughout all frequency bands. Absent or attenuated activity in the “conscious” side suggests sedation or anesthesia. 
• E - EDGE - Observe the activity edge. Significant dips in one hemisphere compared to the other suggest focal brain ischemia.  

Agitation is represented by linear activity depicting intensity of brain activity and position of this activity within the brain topography. Sedation can be effectively titrated until this activity is reduced to normalcy using continuous infusion of sedative agents, while ensuring patient comfort under paralysis as the search for underlying pathology follows. Different classifications and combinations of sedatives, analgesics, or antipsychotics can be tried until the combination that brings about the most appropriately calm cerebral function tracing is discovered. Attention can then be turned to protecting other organs from damage.

RELEVANT ANATOMY

Section 4 of 10  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Several aspects of neuroanatomy and neurophysiology require review in a discussion of TBI. Although a comprehensive review of neuroanatomy is beyond the scope of this discussion, a few key concepts are reviewed.

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 an 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.

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

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, as follows: (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.² 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 clinical 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.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Medical therapy

The treatment of head injury may be divided into the treatment of closed head injury and the treatment of penetrating head injury. While significant overlap exists between the treatments of these 2 types of injury, some important differences are discussed. Closed head injury treatment is divided further into the treatment of mild, moderate, and severe head injuries.

See related CME at Severe Traumatic Brain Injury: Evolution and Current Surgical Management.
 
Closed head injury 

Mild head injury

Moderate and severe head injury

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. Hypocapnea is capable of reducing cerebral blood flow 4% for each mm Hg change in PaCO₂. The control mechanism is probably extravascular pH changes in fluid bathing cerebral resistor vessels, which alter smooth muscle intracellular calcium concentrations. 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.

Below a PaCO₂ of 25-30 Torr, CBF falls much less rapidly, presumably because of severe enough vasoconstriction to induce hypoxemia in brain tissues, limiting oxygen delivery. PaCO₂ tensions less than 25 Torr are sufficient to change brain metabolism into anaerobic, which increases acidosis. Low arterial O₂ tensions influence CBF but to a lesser degree than PaCO₂. No measurable changes in CBF occur during hypoxemia until the PaO₂ drops below 50 Torr, at which time CBF gradually increases. In addition to reducing CBF, the resultant respiratory alkalosis may reverse local tissue acidosis, which develops in cerebral edema, benefiting cellular respiration and restoring autoregulation. Within 48-72 hours, renal mechanisms for handling bicarbonate excretion compensate for altered PaCO₂ tensions, thereby normalizing cerebral pH and returning CBF to baseline values. 

There are 3 paradoxes to hyperventilation therapy for the control of ICP.

• Since cerebral vasospasm is a serious concern in subarachnoid hemorrhage (SAH), attempts to create further vessel constriction by hyperventilation in order to decrease concomitant cerebral edema are rarely indicated unless the amount of edema is clinically emergent.
• Vessels in the damaged area of the brain have lost their autoregulatory control. While unaffected brain regions would vasoconstrict normally to the stimulus of decreased PaCO₂, damaged areas might vasodilate in response to diminished cerebral blood flow. This can create a “reverse steal” phenomenon, where blood and nutrients are diverted away from “normal” areas of the brain and into “damaged” areas. This diversion would feed the increased metabolic requirement of damaged tissues, but the sum total effect may cause more harm to the rest of the brain. In addition, the increased hydrostatic pressure combined with the capillary permeability damage might, in some cases, paradoxically increase ICP in damaged areas.
• Sudden increases in PaCO₂, as a result of ventilator changes, often result in dramatic increases in CBF, and rapid deteriorations in the patient’s condition. During hyperventilation, the cerebral bicarbonate level gradually adjusts to offset the lower level of CO₂, maintaining normal pH. If the pCO₂ is allowed to rise suddenly, the excess CO₂ rapidly crosses the blood-brain barrier, but the bicarbonate level in the brain increases much less rapidly. The result is cerebral acidosis, with attendant cerebral vascular dilatation, increased cerebral blood volume, and elevated ICP, usually resistant to further hyperventilation. 

Unfortunately, little objective evidence exists that treatment by hypocapnea has significantly improved mortality or survival. At best, it seems to be a temporary stop-gap measure until some other curative measure, such as surgery, might be attempted. Patients with the most prompt response to hyperventilation generally have the best prognosis for recovery. No evidence exists that hyperventilation therapy produces benefit in hypoxemic-anoxic encephalopathy.

Diuretics are powerful in their ability to decrease brain volume and, therefore, to 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.

Hypertonic saline (3%) has generated some interest in the treatment of intracranial hypertension secondary to brain edema because it is thought to be less disruptive to fluid and electrolyte balance than other diuretic agents. 

Saline 3% or 7.5% administered in continuous infusion generates a more predictable and gentle osmotic flow of brain intracellular water into the interstitial space. The maximum effect occurs after the end of infusion and is visible over 4 hours. Hypertonic saline hydroxyethyl starch (HS-HES) seems to effectively lower ICP but does not increase CPP as much as does mannitol.  Therapeutically, the limits of serum sodium and osmolality are in the range of 155-320. More research is needed to elucidate the exact method of action of hypertonic saline and the contraindications.  

Other supportive treatments

While awaiting possible operative therapy, other supportive treatments are as follows: 

• Early extraventricular drainage of CSF is sometimes of value in controlling brain edema if there is a suspicion that the ventricles will progressively diminish in size because edema cannot be cannulated from a burr hole.
• Coughing and straining increase venous pressure, restricting drainage and backing up blood into the head, thereby increasing ICP. Neuromuscular paralysis may decrease ICP by preventing sudden changes related to coughing or straining and by promoting systemic venous pooling that increases venous drainage from the head. Any other restrictions to jugular blood drainage, such as a kinked neck from positioning in bed, increase ICP by retarding jugular drainage, transmitting pressure back into the brain.
• Trying to differentiate a drug-induced coma from an increased ICP–induced coma with a trial of naloxone (Narcan) is contraindicated, as it invariably induces agitation if the stupor is narcotic induced. Agitation increases catecholamine response, increases cardiac output, and increases blood flow to the head, thereby increasing hydrostatic pressure and ICP.
• Decreased serum protein (albumin) from malnutrition causes a decreased serum osmolality compared to the osmolality in the surrounding tissues. This allows intravascular water to flow along the increased osmotic gradient into the tissues, increasing edema. Hyperalimentation should be initiated as soon as possible if the course is likely to be protracted.
• Boutique intravenous stabilizing cocktails have been said to maintain homeostasis of intravascular and extravascular fluid compartments, avoiding rapid fluid shifts that might adversely affect cerebral metabolism and edema. Composed of an albumin, bicarbonate, and lasix solution, the albumin increases intravascular colloid content, resisting fluid flow into the brain substance, the bicarbonate buffers pH changes, and the lasix tends to promote a stable, consistent urine output, resisting intravascular fluid changes from renal compensations. This may be useful in diffuse brain edema to protect against further damage from vascular compartment shifts, but body physiology probably adapts to it rapidly, thereby limiting its effect. These cocktails have not been proven to be effective as a treatment of SAH since they tend to promote diuresis and intravascular depletion.

Management of cerebral perfusion pressure

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.

Follow-up

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.

COMPLICATIONS

Section 7 of 10  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Functional deficits resulting from TBI are common and can be divided into 2 categories, as follows: systemic complications and neurologic complications. The systemic complications of TBI are typical of any severe injury and depend on the types of intensive treatments used. Be aware of the complications of intensive care treatment when considering systemic complications of head injury. The neurologic complications of TBI include focal neurologic deficits, global neurologic deficits, seizures, CSF fistulae, hydrocephalus, vascular injuries, infections, and brain death.

Focal neurologic deficits

Focal neurologic deficits are quite common following TBI. Cranial nerves are affected often because of their anatomic location at the base of the brain. When the brain shifts within the skull as it undergoes either acceleration or deceleration forces, significant force is often placed on the entire brain and the cranial nerves. The cranial nerves are tethered at their exit sites from the skull, and, as a result, they may be stretched when the brain shifts as a result of acceleration or deceleration forces. In addition, the cranial nerves are very susceptible to injury as they course through narrow bony canals and grooves. The cranial nerves that are injured most commonly in patients with TBI are cranial nerves I, IV, VII, and VIII.

Anosmia caused by traumatic injury to the first cranial nerve occurs in 2-38% of patients with TBI. It is more common in those with frontal fractures and in those with posttraumatic rhinorrhea. Posttraumatic anosmia improves slowly, and as many as one third of patients do not show any improvement in olfaction.

Injuries to the fourth cranial nerve, the trochlear nerve, are also quite common. This nerve is often injured in patients with head trauma because it has the longest intracranial course of the cranial nerves. Injury to the trochlear nerve causes a positional diplopia, in which those affected experience diplopia when they look down and toward the eye in which the trochlear nerve is injured. As a result, to compensate, the head is tilted up and away from the side of the injury. Trochlear nerve injuries resolve fully in approximately two thirds of those with unilateral injury and in one fourth of those with bilateral injuries.

Facial nerve injuries often occur with head injuries in which the temporal bone is fractured. From 10-30% of persons with longitudinal fractures of the temporal bone and 30-50% of those with transverse fractures of the temporal bone have either acute or delayed facial nerve injury. Immediate facial nerve injury suggests direct injury to the nerve, while delayed injury suggests progressive edema within the nerve. In severely injured patients, a delay in the diagnosis of facial nerve injuries occurs frequently because facial nerve function is difficult to assess in obtunded patients.

Cochlear nerve injury (cranial nerve VIII) is also a common occurrence in patients with head injury, especially in patients with temporal bone fractures. In addition, vestibular disorders, including vertigo, dizziness, and tinnitus, are extremely common in patients with head injuries.

Hydrocephalus

Hydrocephalus is a common late complication of TBI. Posttraumatic hydrocephalus may present as either ventriculomegaly with increased ICP or as normal pressure hydrocephalus. In patients with increased ICP secondary to posttraumatic hydrocephalus, the typical signs of hydrocephalus are often observed and include headaches, visual disturbances, nausea/vomiting, and alterations in the level of consciousness. Normal pressure hydrocephalus usually manifests as memory problems, gait ataxia, and urinary incontinence.

The diagnosis of normal pressure hydrocephalus may be difficult to make in patients with TBI because they often have memory difficulties and gait abnormalities secondary to their head injury. In addition, as many as 86% of patients with TBI demonstrate some degree of ventriculomegaly on follow-up CT scan images. This ventriculomegaly is often secondary to diffuse brain atrophy, and radiographic features rarely help make the distinction between atrophy and normal pressure hydrocephalus. Any patient who develops neurologic deterioration weeks to months following TBI should be evaluated for the possibility of normal pressure hydrocephalus. When CT scan findings cannot help distinguish between normal pressure hydrocephalus and ventriculomegaly secondary to brain atrophy, a high-volume lumbar puncture tap test is performed to ascertain if CSF drainage would improve the patient's neurologic condition.

Seizures

Posttraumatic seizures are a frequent complication of TBI and are divided into 3 categories. Early seizures occur within 24 hours of the initial injury, intermediate seizures occur 1-7 days following injury, and late seizures occur more than 7 days after the initial injury. Posttraumatic seizures are very common in those with a penetrating cerebral injury, and late seizures occur in as many as half of these patients.

Cerebrospinal fluid fistulae

Cerebrospinal fistulae, either in the form of rhinorrhea or otorrhea, may occur in as many as 5-10% of patients with TBI. They may present either immediately or in a delayed fashion and are more frequent in patients with basilar skull fractures. Approximately 80% of acute cases of CSF rhinorrhea resolve spontaneously within 1 week. A 17% risk of meningitis exists when CSF rhinorrhea is present. Prophylactic antibiotics have not been demonstrated to decrease this meningitis risk, although very few studies have examined this issue. More than 95% of acute episodes of CSF otorrhea resolve spontaneously within 1 week, and CSF otorrhea is complicated by meningitis in fewer than 4% of cases.

When acute CSF fistulae do not resolve spontaneously, a lumbar subarachnoid drain may be placed for several days in an attempt to divert CSF and allow the fistula to close. If this fails, radiographic dye is introduced into the subarachnoid space via lumbar puncture (metrizamide cisternogram), and a high-resolution CT scan is performed in an attempt to identify the origin of the CSF fistula. A craniotomy is performed, and the fistula site is repaired. Delayed CSF fistulae may occur from 1 week after the initial injury to years later. These delayed fistulae are more difficult to treat and frequently require surgical intervention.

Vascular injuries

Vascular injuries are uncommon sequelae of TBIs. Arterial injuries that may occur following head trauma include arterial transactions, thromboembolic phenomena, posttraumatic aneurysms, dissections, and carotid-cavernous fistulae (CCF).

Arterial occlusions secondary to transactions or thromboembolism following closed head injuries are uncommon occurrences.

Posttraumatic intracranial aneurysms, which are also rare, differ from congenital aneurysms because the posttraumatic aneurysms tend to be located distally, as opposed to the congenital aneurysms, which are typically proximal in location.

Arterial dissections are more common than the aforementioned arterial injuries and should be considered if significant injury has occurred to the petrous portion of the temporal bone, through which the carotid artery passes, or when an unexplained neurologic deficit is present. A cerebral angiogram is often necessary to help exclude arterial injury in these cases.

Posttraumatic CCF occur when the internal carotid artery is injured within the cavernous sinus, resulting in a direct connection between the carotid artery and the veins of the cavernous sinus. This overloads the venous system and results in chemosis and proptosis on the affected side. Other signs of CCF include diplopia, ophthalmoplegia, visual disturbances, and headaches. Some high-risk fistulae may cause intracerebral hemorrhage. CCF are treated with endovascular balloon occlusion of the fistula origin.

Specific intracranial venous injuries are uncommon following TBI if one excludes the injury to the bridging veins, which are the most common source of subdural hematomas. Depressed skull fractures overlying any of the major intracranial venous sinuses may cause injury to the sinus. When these venous sinus injuries require treatment, substantial, and sometimes life-threatening, blood loss can occur.

A second type of venous injury following TBI involves venous sinus thrombosis. Although very rare following head injury, this is a potentially life-threatening injury because the impaired venous drainage often causes severe ICP elevations and venous infarction. The treatment of venous sinus thrombosis is anticoagulation, which presents significant risk in those with acute head injuries. If the thrombosis progresses despite systemic anticoagulation, direct intracranial intravenous thrombolysis is necessary.

Infections

Intracranial infections are another potential complication of TBI. In uncomplicated closed head injury, infection is uncommon. When basilar skull fractures and/or CSF fistulae are present, the risk of infection is increased. In addition, if a patient has had a ventriculostomy for ICP monitoring, the risk of infection is also increased, for either a ventriculitis or meningitis. Other intracranial infections, such as subdural or epidural empyema and intraparenchymal abscesses, are rare following closed head injury. As one would expect, the incidence of infection in penetrating cerebral injuries and open depressed skull fractures increases.

• Confirm that the patient is in a coma.
• Evaluate the patient for seizure activity and decerebrate or decorticate movements.
• Test for motor response to painful stimulation.
• Test for pupillary response to light.
• Test for corneal reflex. 
• Test for oculocephalogyric reflex (doll’s head reflex).
• Test for vestibulo-ocular reflex (caloric test). 
• Test for upper and lower airway stimulation (eg, pharyngeal and endotracheal suction).
• Test for gag reflex.
• Perform apnea test. This test should be the last test and should be conducted after two clinical examinations (separated by the mandatory observation period) have confirmed the absence of brainstem functions. The patient is disconnected from the ventilator while oxygenation of the lungs is continued passively. On the basis of calculation (whereby PaCO₂ is assumed to rise 4 mm Hg in the first minute and 3 mm Hg every minute thereafter), the patient is allowed to build up to a PaCO₂ of 60 mm Hg or more without becoming hypoxic. If there is no respiratory effort, the apnea test is considered confirmatory.
• Consider an EEG. The EEG should show electrocerebral silence for at least 30 minutes and must conform to established criteria for brain death.
• If the cause of death cannot be determined with absolute accuracy, consider cerebral angiography. The absence of intracranial arterial circulation, as demonstrated by four-vessel angiography, confirms brain death.

Brain death and life support

In earlier times, it could be said that a person was dead when pulseless and apneic. Today, this view no longer suffices. Death is more a process than an event. Lack of blood flow to the brain leads to loss of consciousness within seconds, but other functions of the brain may persist for much longer. Other somatic organs may take hours to stop functioning, and connective tissues can take days to die.

The evolution of life-support systems capable of prolonging death indefinitely necessitated a more accurate definition of death, which arrived in 1968 with the formulation of the Harvard criteria for the working definition of death. In essence, these criteria considered the irreversible loss of brain function, rather than whole-body metabolic cessation, to be indicative of death. When the Harvard criteria were met, death was inevitable, even with continuing treatment. The Harvard criteria objectified the progression of disease, thereby making it possible for clinicians to