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Introduction to CNS Imaging, Trauma
Approach to Head Trauma
General Considerations
Epidemiology : Trauma is the most common worldwide cause of death and disability in children and young adults. In these patients, neurotrauma is responsible for the vast majority of cases. In the USA and Canada, emergency departments (ED) treat more than 8 million patients with head injuries annually, representing 6-7% of all ED visits.
The vast majority of patients with head trauma are classified as having minimal or minor injury. Minimal head injury is defined as no neurologic alteration or loss of consciousness (LOC). Minor head injury or concussion is epitomized by a walking, talking patient with a Glasgow Coma Score (GCS) of 13-15, who has experienced LOC, amnesia, or disorientation.
Of all head-injured patients, ~ 10% sustain fatal brain injury, whereas another 5-10% of neurotrauma survivors have permanent serious neurologic deficits. A number have more subtle deficits (“minimal brain trauma”), whereas 20-40% of patients have moderate disability.
Etiology and Mechanisms of Injury
The etiology of traumatic brain injury (TBI) varies according to patient age. Falls are the leading cause of TBI in children younger than 4 years and in elderly patients older than 75 years. Gunshot wounds are most common in adolescent and young adult male patients but relatively rare in other groups. Motor vehicle and auto-pedestrian collisions occur at all ages without gender predilection.
TBI can be a missile or nonmissile injury. Missile injury results from penetration of the skull, meninges, &/or brain by an external object (such as a bullet).
Nonmissile closed head injury (CHI) can be caused by direct blows, blasts, or penetrating injuries. However, nonmissile CHI is a more common cause of neurotrauma. High-speed accidents exert significant acceleration/deceleration forces, causing the brain to move suddenly within the skull. Forcible impaction of the brain against the unyielding calvaria and hard, knife-like dura results in gyral contusion. Rotation and abrupt changes in angular momentum may deform, stretch, and damage long vulnerable axons, resulting in axonal injury.
Classification of Head Trauma
The most widely used clinical classification of brain trauma, the GCS, depends on the assessment of 3 features: Best eye, verbal, and motor responses. With the use of the GCS, TBI can be designated as mild (13-15), moderate (9-12), or severe (≤ 8).
TBI can also be divided pathoetiologically into primary and secondary injuries. Primary injuries occur at the time of initial trauma. Skull fractures, epi- and subdural hematomas, contusion, and axonal injuries are examples of primary traumatic injuries.
Secondary injuries occur later and include cerebral edema, perfusions, and brain herniations. Large arteries, such as the internal carotid, vertebral, and middle meningeal arteries, can be injured either directly at the time of initial trauma or indirectly as a complication of brain herniations.
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