Almost 10 million head injuries occur annually in the United States, about 20% of which are serious enough to cause brain damage. Among men <35 years, accidents, usually motor vehicle collisions, are the chief cause of death and >70% of these involve head injury. Furthermore, minor head injuries are so common that almost all physicians will be called upon to provide immediate care or to see patients who are suffering from various sequelae.
Medical personnel caring for head injury patients should be aware that (1) spinal injury often accompanies head injury, and care must be taken in handling the patient to prevent compression of the spinal cord due to instability of the spinal column; (2) intoxication is frequently associated with traumatic brain injury, and thus testing for drugs and alcohol should be carried out when appropriate; and (3) additional injuries, including rupture of abdominal organs, may produce vascular collapse, shock, or respiratory distress that requires immediate attention.
This form of minor head injury had in the past referred to an immediate and transient loss of consciousness that was associated with a short period of amnesia. Many patients, however, do not lose consciousness after a minor head injury but instead are dazed or confused, or feel stunned or “star struck,” and the term concussion is now applied to all such cognitive and perceptual changes experienced after a blow to the head. Severe concussion may precipitate a brief convulsion or autonomic signs such as facial pallor, bradycardia, faintness with mild hypotension, or sluggish pupillary reaction, but most patients quickly return to a neurologically normal state.
The mechanics of a typical concussion involve sudden deceleration of the head when hitting a blunt stationary object. This creates an anterior-posterior movement of the brain within the skull due to inertia and rotation of the cerebral hemispheres on the fulcrum of the relatively fixed upper brainstem. Loss of consciousness in concussion is believed to result from a transient electrophysiologic dysfunction of the reticular activating system in the upper midbrain that is at the site of rotation (Chap. 19). The transmission of a wave of kinetic energy throughout the brain is an alternative explanation for the disruption in consciousness.
Gross and light-microscopic changes in the brain are usually absent following concussion, but biochemical and ultrastructural changes, such as mitochondrial ATP depletion and local disruption of the blood-brain barrier, may be transient abnormalities. Computed tomography (CT) and magnetic resonance imaging (MRI) scans are usually normal; however, a small number of patients will be found to have a skull fracture, an intracranial hemorrhage, or a brain contusion.
A brief period of both retrograde and anterograde amnesia is characteristic of concussion, and it recedes rapidly in alert patients. Memory loss spans the moments before impact but may encompass the previous days or weeks (rarely months). With severe injuries, the extent of retrograde amnesia roughly correlates ...