Traumatic brain injuries (TBIs) are sustained through a variety of mechanisms. The three broad classifications are discussed in Table 4.1 .
| Penetrating Brain Injury |
| A head injury that results from a projectile or object that penetrates through the skull and dura mater. The most common cause is gunshot wounds, but low-velocity objects such as knives and skull fragments are also capable of causing penetrating injury. , |
| Nonpenetrating or Closed/Blunt Injury |
| A head injury that results from direct impact to the skull. This produces linear and rotational forces that are exerted through the brain, resulting in damage to both neuronal and vascular structures. Falls and motor vehicle accidents are the two leading causes of closed injury. , |
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| Blast Injury |
| A head injury that results from a blast wave created by an explosion. The blast wave causes rapid changes in intracranial pressure, which results in axonal, capillary, and brain tissue damage. Air−fluid interfaces are most susceptible to damage. Improvised explosive devices are the most common cause of blast injury. |
Understanding the underlying mechanism of injury can help guide prognosis and treatment. Please note that most established guidelines relate specifically to closed or nonpenetrating head injuries, and this injury pattern is covered more extensively in other chapters. In this chapter we will review the unique features and key differences of both penetrating and blast injury.
Penetrating brain injury
Epidemiology
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Penetrating brain injury (PBI) is the deadliest form of TBI.
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It is estimated that 70% to 90% of victims will die before arrival to the hospital, and approximately 50% more will die during resuscitation attempts in the emergency department.
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The prognosis for PBI is worse than that of closed brain injury, but it is far less prevalent.
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Based on data from the Department of Defense (DoD), PBI was responsible for only 1.4% of all TBIs sustained by the military between the years 2000 to 2018.
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Gunshot wounds are the leading cause of PBI overall and account for 12% of all TBIs.
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In the United Sates it is estimated that 32,000 to 35,000 civilians die each year from PBI.
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The incidence of PBI is on the rise and is attributed to an increase in gun violence and suicide.
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In 2016” the Centers for Disease Control and Prevention (CDC) reported a 6.3% increase in firearm mortality rate from 2015 to 2016, with suicide and homicide accounting for 59.3% and 37.3% of the total firearm deaths, respectively.
Mechanism of injury
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PBI is most commonly caused from a firearm projectile; see Table 4.2 for various types of penetrating injuries and Fig. 4.1 for illustration of common patterns of PBI.
TABLE 4.2
Penetrating Brain Injury Wound Patterns
From Vakil MT, Singh AK. A review of penetrating brain trauma: epidemiology, pathophysiology, imaging assessment, complications, and treatment. Emerg Radiol. 2017;24(3):301-309.
Does not penetrate brain parenchyma
Tangential
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Projectile that strikes the skull at an angle, resulting in superficial scalp damage without penetrating through bone
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Can cause skull fracture and cerebral contusion
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Wound pattern associated with best prognosis
Careening
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Projectile penetrates the skull but travels along the periphery of the cortex without penetrating the brain parenchyma
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Rare wound pattern
Penetrates brain parenchyma
Penetrating
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Projectile penetrates the skull and brain parenchyma but does not exit
Perforating
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Projectile enters the skull and brain parenchyma and then exits at a distal site
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Most lethal form of penetrating brain injury
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Typically caused by close range or high-velocity projectile
Ricochet
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Projectile enters brain parenchyma and then bounces off the inner aspect of the skull forming new wound tract
• Fig. 4.1
Common patterns of penetrating brain injury.
(From Vakil MT, Singh AK. A review of penetrating brain trauma: epidemiology, pathophysiology, imaging assessment, complications, and treatment. Emerg Radiol. 2017;24[3]:301-309. Illustration by Nicholas Vlahos, DO.)
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Kinetic energy is transferred through the projectile into the human skull and brain parenchyma.
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The equation for kinetic energy is E k = 1/2 mv 2 , where m = mass and v = speed.
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Based on this formula, it is clear that the speed of an object has a greater impact on kinetic energy than its overall mass.
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This explains why small high-speed projectiles from a firearm often produce greater damage than slow-speed projectiles like knives, which are greater in mass.
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Other important factors that contribute to gunshot wound severity include the shape of the projectile, tumbling, and the firing distance.
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Shorter firing distances result in less kinetic energy loss before the time of impact and therefore maximize energy transfer to skull and brain.
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Suicide-related PBI typically occur at close range and carries a high mortality rate of approximately 95%.
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Pathophysiology
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PBI is the result of immediate neuronal and vascular destruction from a traversing projectile through the brain parenchyma.
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This causes permanent cavitation and is followed by high-pressure waves that cause hemorrhage and neuronal membrane disruption at sites distant to the projectile’s primary trajectory.
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Cerebral edema rapidly develops and intracranial pressure increases resulting in cerebral ischemia.
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Multiple factors contribute to, the mortality rate of PBI; see Table 4.3 for a brief review.
TABLE 4.3Related posts:
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