Gunshot Wound Head Trauma

OVERVIEW

U.S. Statistics

• Of all TBIs, 12% are attributed to firearms.
• In people ages 25-34, firearms are a leading cause of TBI.
• Gunshot wounds to the head are the cause of an estimated 35% of all deaths attributed to TBI.
• Gunshot wounds to the head are fatal about 90% of the time, with many victims dying before arriving to the hospital.
• For victims who survive the initial trauma, about 50% die in the emergency room.
• About 50% of surviving patients will suffer from seizures and require anti-epilepsy medication
• Gunshot wounds to the head survivors need long-term rehabilitation and may or may not be able to get back to pre-injury functional status.

Brain Injury

A wound in which the projectile enters the cranium, but does not exit, is referred to as a penetrating wound. An injury in which the projectile enters and exits the cranium is referred to as a perforating wound.

When the projectile itself goes through the brain, there is injury from both the direct penetration of the brain and from transmission of a pressure wave from the high-velocity (greater than 2,000 feet/second) projectile traveling through the brain tissue. Both bleeding and damage from this pressure wave results in brain swelling, which can also lead to death.

A number of factors determine the extent of damage caused by a gunshot wound. These include the caliber of the gun, size and speed of the bullet, the trajectory and site of the injury. A bullet wound going through the right frontal lobe tip toward the forehead and well above the base of the skull is likely to cause relatively mild clinical damage, because it passes through no vital brain tissue or vascular structures. However, a similar bullet passing downward from the left frontal lobe tip toward the temporal lobe and brainstem is likely to be devastating, because it passes through eloquent brain tissue and is likely to injure important vascular structures inside the head. A bullet trajectory through key blood vessels in the brain can result in rapidly expanding blood clot in the brain that can critically compress the important brain tissue resulting in immediate death at the scene. If the victim survives the initial insult, the issue becomes the increasing pressure inside the skull.

Surgical Treatment

Gunshot wound head trauma patients are aggressively resuscitated upon initial arrival at the hospital. If blood pressure and oxygenation can be maintained, an urgent CT scan of the head is obtained. The decision to proceed with surgical treatment of the gunshot wound is based on the following factors:

• The level of consciousness: Glascow Coma Scale (GCS) 1-15; a patient with any score less than 7 or 8 is considered to be in coma;
• The degree of brainstem neurological function; and
• CT scan findings.

If patients are deeply comatose with minimal evidence of brainstem function and without evidence of an intracranial hematoma that might be causing coma, a fatal outcome is nearly certain. If a hematoma is confirmed by CT scan, an emergency craniotomy for clot evacuation, removal of debris and devitalized tissue may be performed. It is common for pressure to build up within the skull, so a craniectomy (a procedure in which a large portion of the skull is temporarily removed to decrease pressure inside the skull) is also often performed.

Understanding the trajectory of the bullet path is important in determining prognosis and management. The brain is divided into two hemispheres made up of four lobes each, with each lobe providing different functions. Additionally, there are deeper parts of the brain that house many connections, controlling basic body and brain functions. The brainstem contains nuclei for cranial nerves needed for basic functions, such as breathing and swallowing. It connects the upper portion, or “thinking” portions of the brain, to the spinal cord. The cerebellum, in the back lower part of the brain, is related to motor coordination.

Outcomes

Outcome is poorer for those with extensive bullet tracts, those that cross the deep midline structures of the brain or those that involve the brainstem. A bullet that damages the patient’s right hemisphere can leave the victim with motor and sensory impairments on the left side and vice versa. Many other functions such as cognition, memory, speech and vision are controlled by both sides of the brain. As a result, damage to one hemisphere can leave a person impaired but still able to perform these functions at some level, depending on which lobes of the brain are damaged.

Because each hemisphere is divided into four lobes, the “best-case scenario” is a more superficial injury limited to one hemisphere and a single lobe, limiting the functional impairments caused by the trauma. The first week or two after trauma is the acute and critical-care stage. After that, the extent and speed of recovery depends on how much tissue was damaged, the degree of swelling, pressure inside the head during the acute stage and the functional consequences of the damage. Intensive rehabilitation may be necessary to help survivors regain some of their functions or to adapt to permanent deficits. Neurological recovery may require several months or even years.

Factors Contributing to Initial Injury and Outcomes

• The bullet entry and/or exit site.
• The areas of the brain damaged by the trauma.
• Degree of fragmentation of the bullet.
• Caliber of the bullet and type of weapon [high velocity — military assault rifles and hunting rifles (bullet speed greater than 2,000 feet/second); low velocity — handguns (bullet speed less than 2,000 feet/second)].
• Range of the gunshot wound (distance between the gun and the victim).
• Timeliness of receiving proper treatment.
• The victim’s age and general health.
• Initial GCS score.
• Reactivity and dilation state of pupils.
• Status of brainstem reflexes.
• Blood pressure.
• Oxygenation state right after injury.

References

1. eMedicine, Ainsworth, C. R. (2020, November 30). Head Trauma: Background, Pathophysiology, Etiology. Medscape. https://emedicine.medscape.com/article/433855-overview
2. Cranial GunShot Wounds – UCLA Neurosurgery, Los Angeles. (n.d.). UCLA Health. Retrieved May 26, 2021, from https://www.uclahealth.org/neurosurgery/cranial-gunshot-wounds
3. Aarabi, B., Tofighi, B., Kufera, J. A., Hadley, J., Ahn, E. S., Cooper, C., Malik, J. M., Naff, N. J., Chang, L., Radley, M., Kheder, A., & Uscinski, R. H. (2014). Predictors of outcome in civilian gunshot wounds to the head. Journal of Neurosurgery, 120(5), 1138–1146.
4. Ecker, R. D., Mulligan, L. P., Dirks, M., Bell, R. S., Severson, M. A., Howard, R. S., & Armonda, R. A. (2011). Outcomes of 33 patients from the wars in Iraq and Afghanistan undergoing bilateral or bicompartmental craniectomy. Journal of Neurosurgery, 115(1), 124–129.