Background
Traumatic brain
injury (TBI) is the fourth leading cause of death in the United States
and is the leading cause of death in persons aged 1-44 years.
Approximately 2 million traumatic brain injuries occur each year, and an
approximate $25 billion per year is spent in social and medical
management of people with such injuries.
Analysis of the trauma
literature has shown that 50% of all trauma deaths are secondary to
traumatic brain injury (TBI), and gunshot wounds to the head caused 35%
of these. The current increase in firearm-related violence and
subsequent increase in penetrating head injury remains of concern to
neurosurgeons in particular and to the community as a whole.
The CT scan below is of a patient after a gunshot wound to the brain.
A young man arrived in the emergency department after experiencing a
gunshot wound to the brain. The entrance was on the left occipital
region. A CT scan shows the skull fracture and a large underlying
cerebral contusion. The patient was taken to the operating room for
debridement of the wound and skull fracture, with repair of the dura
mater. He was discharged in good neurological condition, with a
significant visual field defect.
The
definition of a penetrating head trauma is a wound in which a
projectile breaches the cranium but does not exit it. Despite the
prevalence of these injuries, the morbidity and mortality of penetrating
head injury remains high. Improvements in the understanding of the
mechanisms of injury and aggressive medical and surgical management of
patients with these injuries may lead to improved outcomes.
This
chapter focuses on the pathophysiology of both primary and secondary
mechanisms of injury, describes the treatment of patients from
presentation to discharge, and concludes with a discussion of possible
complications and patient outcome. For excellent patient education
resources, visit eMedicine's Brain and Nervous System Center. Also, see eMedicine's patient education article Brain Infection.
History of the Procedure
The
earliest reported series of head injuries and their management appears
in the Edwin Smith papyrus around 1700 BC, reporting 4 depressed skull
fractures treated by the Egyptians by leaving the wound unbandaged,
providing free drainage of the intracranial cavity, and anointing the
scalp wound with grease. Hippocrates (460-357 BC) performed trephination
for contusions, fissure fractures, and skull indentations. Galen's
experience in 130-210 AD treating wounded gladiators led to recognition
of a correlation between the side of injury and the side of motor loss.
During
the Dark Ages, little progress was made in the surgical management of
head wounds and medicine continued to hold a pessimistic view of head
wounds with torn dura mater. In the 17th century, Richard Wiseman
provided a better understanding of surgical management of penetrating
brain injuries; he recommended the evacuation of subdural hematomas and the extraction of bone fragments. In his experience, deep wounds had a much worse prognosis than superficial ones.
Major
advances in the management of penetrating craniocerebral injuries in
the mid-19th century were related to the work of Louis Pasteur (1867),
Robert Koch in bacteriology (1876), and Joseph Lister in asepsis (1867).
Such advances dramatically reduced the incidence of local and systemic
infections, as well as mortality.
Problem
In
the past 20 years, a dramatic increase in the incidence of penetrating
injuries to the brain has occurred. Gunshot wounds to the head have
become the leading or second leading cause of head injury in many cities
in the United States. These injuries are devastating to the patient,
family, and society.
Siccardi et al (1991) prospectively studied a
series of 314 patients with craniocerebral missile wounds and found
that 73% of the victims died at the scene, 12% died within 3 hours of
injury, and 7% died later, yielding a total mortality of 92% in his
series.In another study, gunshot wounds were responsible for at least 14% of the head injury-related deaths from 1979-1986.
Age-adjusted
death rates for injury by firearms have increased nearly every year
since 1985. A study using multiple logistic regressions found that
injury from firearms greatly increases the probability of death and that
the victim of a gunshot wound to the head is approximately 35 times
more likely to die than is a patient with a comparable nonpenetrating brain injury.
Epidemiology
Frequency
A
National Institutes of Health survey estimates that in the United
States, 1.9 million persons annually experience a skull fracture or
intracranial injury, and, of these cases, one-half have a suboptimal
outcome. In 1992, firearms accounted for the largest proportion of
deaths from traumatic brain injury in the United States, and gunshot
wounds were the most common cause of mortality in African Americans.
Etiology
Penetrating
head injuries can be the result of numerous intentional or
unintentional events, including missile wounds, stab wounds, and motor
vehicle or occupational accidents (nails, screwdrivers).
Stab
wounds to the cranium are typically caused by a weapon with a small
impact area and wielded at low velocity. The most common wound is a
knife injury, although bizarre craniocerebral-perforating injuries have
been reported that were caused by nails, metal poles, ice picks, keys,
pencils, chopsticks, and power drills.
Pathophysiology
The
pathological consequences of penetrating head wounds depend on the
circumstances of the injury, including the properties of the weapon or
missile, the energy of the impact, and the location and characteristics
of the intracranial trajectory. Following the primary injury or impact,
secondary injuries may develop. Secondary injury mechanisms are defined
as pathological processes that occur after the time of the injury and
adversely affect the ability of the brain to recover from the primary
insult. A biochemical cascade begins when a mechanical force disrupts
the normal cell integrity, producing the release of numerous enzymes,
phospholipids, excitatory neurotransmitters (glutamate), Ca, and free
oxygen radicals that propagate further cell damage.
Missile wounds
Missiles
range from low-velocity bullets used in handguns, as shown in the image
below, or shotguns to high-velocity metal-jacket bullets fired from
military weapons.Low-velocity
civilian missile wounds occur from air rifle projectiles, nail guns
used in construction devices, stun guns used for animal slaughter, and
shrapnel produced during explosions. Bullets can cause damage to brain
parenchyma through 3 mechanisms: (1) laceration and crushing, (2)
cavitation, and (3) shock waves. The injury may range from a depressed fracture of the skull resulting in a focal hemorrhage to devastating diffuse damage to the brain.
A 65-year-old man experienced a gunshot wound to the right
frontoparietal region. A CT scan shows that the bullet crossed the
midline, lacerated the superior longitudinal sinus, and produced a large
midline subdural hematoma. The patient presented with a Glasgow Coma
Scale (GCS) score of 4 and died.
As stated previously, a wound in which the projectile breaches the
cranium but does not exit is described technically as penetrating, and
an injury in which the projectile passes entirely though the head,
leaving both entrance and exit wounds, is described as perforating. This
distinction has some prognostic implications. In a series of
missile-related head injuries during the Iran-Iraq war, a poor
postsurgical outcome occurred in 50% of patients treated for perforating
wounds, as compared with only 20% of those with penetrating wounds.
In
missile wounds, the amount of damage to the brain depends on numerous
factors including (1) the kinetic energy imparted, (2) the trajectory of
the missile and bone fragments through the brain, (3) intracranial
pressure (ICP) changes at the moment of impact, and (4) secondary
mechanisms of injury. The kinetic energy is calculated employing the
formula 1/2mv
2, where m is the bullet mass and v is the impact velocity.
At
the time of impact, injury is related to (1) the direct crush injury
produced by the missile, (2) the cavitation produced by the centrifugal
effects of the missile on the parenchyma, and (3) the shock waves that
cause a stretch injury. As a projectile passes through the head, tissue
is destroyed and is either ejected out of the entrance or exit wounds or
compressed into the walls of the missile tract. This creates both a
permanent cavity that is 3-4 times larger than the missile diameter and a
pulsating temporary cavity that expands outward. The temporary cavity
can be as much as 30 times larger than the missile diameter and causes
injury to structures a considerable distance from the actual missile
tract.
Stab wounds
This group of wounds, example depicted
below, represents a smaller fraction of penetrating head injuries. The
causes may be from knives, nails, spikes, forks, scissors, and other
assorted objects. Penetrations most commonly occur in the thin bones of
the skull, especially in the orbital surfaces and the squamous portion
of the temporal bone. The mechanisms of neuronal and vascular injury
caused by cranial stab wounds may differ from those caused by other
types of head trauma.
Unlike missile injuries, no concentric zone of coagulative necrosis
caused by dissipated energy is present. Unlike motor vehicle accidents,
no diffuse shearing injury to the brain occurs
A CT scan of a young female who presented to the emergency department
with a stab wound to the head produced by a large knife shows the extent
of intracranial damage, which affects midline structures.
Unless an associated hematoma or infarct is present, cerebral damage
caused by stabbing is largely restricted to the wound tract. A narrow
elongated defect, or so-called slot fracture, sometimes is produced by a
stab wound and is diagnostic when identified. However, in some cases in
which skull penetration is proven, no radiological abnormality can be
identified. In a series of stab wounds, de Villiers (1975) reported a
mortality of 17%, mostly related to vascular injury and massive
intracerebral hematomas.
Stab
wounds to the temporal fossa are more likely to result in major
neurological deficits because of the thinness of the temporal squama and
the shorter distance to the deep brain stem and vascular structures.
Patients in whom the penetrating object is left in place have a
significantly lower mortality than those in whom the objects are
inserted and then removed (26% versus 11% respectively).
Skull perforations and fractures
The
local variations in thickness and strength of the skull and the angle
of the impact determine the severity of the fracture and injury to the
brain, as shown below. Impacts striking the skull at nearly
perpendicular angles may cause bone fragments to travel along the same
trajectory as the penetrating object, to shatter the skull in an
irregular pattern, or to produce linear fractures
that radiate away from the entry defect. Grazing or tangential impacts
produce complex single defects with both internal and external beveling
of the skull, with varied degrees of brain damage.
Lateral skull x-ray film of a patient who presented with a severe intracranial injury produced by a golf club.
The patient presented to the emergency department with a golf club in his head. The club was removed in the operating room.
Presentation
The
clinical condition of the patient depends mainly on the mechanism
(velocity, kinetic energy), anatomical location of the lesions, and
associated injuries.
Traumatic intracranial hematomas
These
can occur alone or in combination and constitute a common and treatable
source of morbidity and mortality resulting from brain shift, brain
swelling, cerebral ischemia, and elevated ICP. Patients present with the
signs and symptoms of an expanding intracranial mass, and the clinical
course varies according to the location and rate of accumulation of the
hematoma. The classic clinical picture of epidural hematomas is
described as involving a lucid interval following the injury; the
patient is stunned by the blow, recovers consciousness, and lapses into
unconsciousness as the clot expands.
Epidural hematomas
Most
traumatic epidural hematomas become rapidly symptomatic with
progression to coma. Acute subdural hematoma occurs in association with
high rates of acceleration and deceleration of the head that takes place
at the time of trauma. This remains one of the most lethal of all head
injuries because the impact causing acute subdural hematoma commonly
results in associated severe parenchymal brain injuries.
Intracerebral hematomas
These
result from direct rupture of small vessels within the parenchyma at
the moment of impact. Patients typically present with a focal
neurological deficit related to the location of the hematoma or with
signs of mass effect and increased ICP. The occurrence of delayed
traumatic intracerebral hematomas is well documented in the literature.
Delayed intracerebral hematomas
The
time interval for the development of delayed intracerebral hematomas
ranges from hours to days. Although these lesions may develop in areas
of previously demonstrated contusion, they frequently occur in the
presence of completely normal results on the initial computed tomography
(CT) scan. Patients with this diagnosis typically meet the following
criteria: (1) a definite history of trauma, (2) an asymptomatic
interval, and (3) an apoplectic event with sudden clinical
deterioration.
Contusions
These consist of areas of
perivascular hemorrhage about small blood vessels and necrotic brain.
Typically, they assume a wedgelike shape, extending through the cortex
to the white matter. When the pia-arachnoid layer is torn, the injury is
termed a cerebral laceration. Clinically, cerebral contusions serve as
niduses for delayed hemorrhage and brain swelling, which can cause
clinical deterioration and secondary brain injury.
Traumatic subarachnoid hemorrhage
This
type of hemorrhage usually is a result of various forces that produce
stress sufficient to damage superficial vascular structures running in
the subarachnoid space. Traumatic subarachnoid hemorrhage
may predispose to cerebral vasospasm and diminished cerebral blood
flow, thereby increasing morbidity and mortality as a result of
secondary ischemic damage.
Diffuse axonal injury or shearing injury
This
has become recognized as one of the most important forms of primary
injury to the brain. In the most extreme form, patients present with
immediate prolonged unconsciousness from the moment of injury and
subsequently remain vegetative or severely impaired.
Indications
A
critical factor in early treatment decisions and in long-term outcome
after penetrating head injuries is the patient's initial level of
consciousness. Although many methods of defining level of consciousness
exist, the most widely used measure is the Glasgow Coma Scale (GCS)
introduced by Teasdale and Jennett in 1974.
Table. Glasgow Coma Scale
Points | Eye Opening | Best Verbal | Best Motor |
6 | … | … | Follows commands |
5 | … | Appropriate | Localizes pain |
4 | Spontaneous | Inappropriate | Withdraws to pain |
3 | In response to voice | Moaning | Flexion (decorticate) |
2 | In response to pain | Incomprehensible | Extension (decerebrate) |
1 | None | None | None |
The level of consciousness can be lowered independent of head injury for numerous reasons, including shock, hypoxia, hypothermia,
alcohol intoxication, postictal state, and administration of sedatives
or narcotics. Therefore, a more reliable assessment of severity and,
thus a more meaningful predictor of outcome, is provided by the
postresuscitation GCS score (hereafter referred to as GCS), which
generally refers to the best level obtained within the first 6-8 hours
of injury following nonsurgical resuscitation. This allows patients to
be categorized into 3 levels, as follows:
Minor or mild injury includes those patients with an initial level of 13-15.
Moderate injury includes patients with a score of 9-12.
Severe injury refers to a postresuscitation level of 3-8 or a subsequent deterioration to 8 or less.
Patients
with severe head injury typically fulfill the criteria for coma, have
the highest incidence of intracranial mass lesions, and require
intensive medical and, often, surgical intervention.
Relevant Anatomy
Penetrating
objects to the cranium must traverse through the scalp, through the
skull bones, and through the dura mater before reaching the brain.
The
scalp consist of 5 different anatomical layers that include the skin
(S); the subcutaneous tissue (C); the galea aponeurotica (A), which is
continuous with the musculoaponeurotic system of the frontalis,
occipitalis, and superficial temporal fascia; underlying loose areolar
tissue (L); and the skull periosteum (P).
The subcutaneous layer
possesses a rich vascular supply that contains an abundant communication
of vessels that can result in a significant blood loss when the scalp
is lacerated. The relatively poor fixation of the galea to the
underlying periosteum of the skull provides little resistance to shear
injuries that can result in large scalp flaps or so-called scalping
injuries. This layer also provides little resistance to hematomas or
abscess formation, and extensive fluid collections related to the scalp
tend to accumulate in the subgaleal plane.
The bones of the
calvaria have 3 distinct layers in the adult—the hard internal and
external tables and the cancellous middle layer, or diploë. Although the
average thickness is approximately 5 mm, the thickest area is usually
the occipital bone and the thinnest is the temporal bone. The calvaria
is covered by periosteum on both the outer and inner surfaces. On the
inner surface, it fuses with the dura to become the outer layer of the
dura.
Aesthetically, the frontal bone is the most important
because only a small portion of the frontal bone is covered by hair. In
addition, it forms the roof and portions of the medial and lateral walls
of the orbit. Displaced frontal fractures therefore may cause
significant deformities, exophthalmus, or enophthalmos. The frontal bone
also contains the frontal sinuses, which are paired cavities located
between the inner and outer lamellae of the frontal bone. The lesser
thickness of the anterior wall of the frontal sinus makes this area more
susceptible to fracture than the adjacent tempora-orbital areas.
The
dura mater or pachymeninx is the thickest and most superficial meninx.
It consists of 2 layers—a superficial layer that fuses with the
periosteum and a deeper layer. In the same region between both layers,
large venous compartments or sinuses are present. A laceration through
these structures can produce significant blood loss or be responsible
for producing epidural or subdural hematomas.