Anatomy and Physiology Review
- Anatomy of the skull and protective meninges of the brain
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- Anatomy of the brain
Pathophysiology
- Head trauma can occur as a result of the same forces that damage other body tissues. Blunt force trauma and penetrating trauma both are common causes.
- Head injuries can be limited to superficial tissues, as in a scalp injury, or consist of damage to deeper structures, as in skull fractures or actual brain injuries.
- Trauma, both blunt force and penetrating, can damage specific structures such as jaw, nose, eyes and ears. These structures commonly are damaged in a similar fashion to other soft tissue injuries and fractures.
- Injuries to the neck, mouth and jaw can result in airway threats.
- Injuries to the eye and ear can threaten vision and hearing.
- Neck injuries can result in spinal damage and also massive hemorrhage due to the superficial location of very large blood vessels. The neck can be damaged by both blunt force and penetrating trauma.
- Primary brain injuries occur as a result of immediate trauma. Structures are damaged by blunt or penetrating trauma.
- Secondary injuries occur after the initial trauma and typically result from hypoxia, hypoperfusion, or swelling in the closed compartment of the skull.
- Rising intracranial pressure results when swelling or bleeding causes the pressure inside the skull to increase to dangerous levels. This pressure can damage brain tissue.
- Because bleeding sometimes occurs slowly, increased intracranial pressure can occur hours after the initial injury.
- Herniation occurs when intracranial pressure becomes so great that it forces the brainstem downward toward the opening of the base of the skull. This commonly results in patient posturing and breathing pattern changes.
- Open head injuries occur when the skull is fractured or penetrated. Closed head injuries occur when the skull remains intact.
- Traumatic brain injuries can be categorized as follows:
- Concussion: Occurs when blunt force trauma is transmitted through the brain and temporarily disturbs brain function.
- Diffuse axonal injury: Occurs when blunt force trauma disturbs nervous transmission and function over a large area of the brain.
- Contusion: Occurs when trauma ruptures small blood vessels in the brain and its protective layers.
- Hematoma: Occurs when blood builds up as a result of damaged blood vessels in the brain and its protective layers. Here bleeding is more extensive than in a contusion.
- Laceration: Occurs when brain tissue is penetrated, cut, and torn, typically from penetrating trauma (however, it can be caused by blunt force trauma).
Signs and Symptoms
- Head injuries may be visible on the external scalp. Consider assessing any other soft tissue. Contusions, hematomas, lacerations and penetrations may be visible. Skull and jaw fractures may display obvious deformity.
- Not all brain injuries will have dramatic physical findings. Often, more subtle findings will point to injuries inside the skull.
- Mental status often can identify disruption of brain function after trauma. Initial or brief loss of consciousness commonly points to concussions and diffuse axonal injuries, and ongoing and increasing altered mental status commonly is associated with rising intracranial pressure.
- The Glasgow Coma Scale provides a standardized score for eye opening, verbal response and motor response that can be used to immediately assess mental status and to track changes and trends over time.
- Head injuries can result in vision and hearing disturbances and can affect balance. Nausea and vomiting are also common side effects.
- Fractures of the skull often can lead to other visible findings, such as bleeding from the nose or ears. Skull fractures can also release clear cerebral spinal fluid that can leak from the ears. In addition, other visible findings can occur over time.
- Battle’s sign is the presence of bleeding behind the ears.
- Raccoon sign is the presence of bleeding around the eyes.
- Rising intracranial pressure can affect pupil reactivity and equality and can cause a pattern of blood pressure, heart rate and breathing changes.
- Cushing’s reflex is caused by increasing intracranial pressure and is identified by a decreasing pulse rate, increasing blood pressure and the emergence of breathing patterns such as Cheyne Stokes breathing.
- Rising intracranial pressure also can cause seizures and autonomic posturing of the extremities.
- Decorticate posturing occurs when the extremities and neck flex in toward the core.
- Decerebrate posturing occurs when the extremities and neck extend away from the core.
Treatment
- Use mechanism of injury to examine the force that resulted in injury.
- Always consider the need for spinal precautions and spinal motion restriction in the context of head injuries.
- Aggressively manage airway issues and ensure adequate breathing. Anticipate airway issues with injuries to the jaw and neck.
- Consider high-concentration oxygen, and be vigilant in preventing hypoxia.
- Treat external injuries to the scalp like other soft tissue injuries. Treat hemorrhage and bandage wounds. Stabilize impaled objects. Do not apply direct pressure if deformity is present. Apply occlusive dressings to large open wounds of the neck.
- Monitor mental status carefully and beware of changes over time.
- Be prepared for vomiting. Have suction ready.
- Transport patients with head elevated if possible. Keep patients calm.
Key Concepts
- The findings associated with brain injury often are subtle and occur over time. Be thorough in initial assessment and vigilant with reassessment. Use mechanism of injury to predict possible injuries.
- Mental status is a particularly valuable indicator of brain injury. Note even small changes as relevant findings.
- Do not allow head-injured patients to become hypoxic. Even brief episodes of hypoxia commonly are associated with increased mortality rates.
- Recognize the patterns associated with rising intracranial pressure. Recall that these findings often are not immediate and generally are identified by trends in assessment.
- Concussions, even if mental status changes are brief and resolved, are serious conditions that warrant further evaluation.
- Signs of herniation (seizures, posturing, Cushing’s reflex) are ominous and are associated with extensive injury.