Brain
injury is often defined differently in
published reports. Although many authors use the term brain injury to
mean acute traumatic damage to the central nervous system (CNS), others
use the term head injury, which allows inclusion of skull injuries,
fractures, or soft tissue damage to the face or head without any
obvious neurologic consequences. Kraus
et Al define brain injury as
"physician-diagnosed physical damage from acute mechanical energy
exchange resulting in concussion, hemorrhage, contusion, or laceration
of the brain."1 For excellent patient education resources, visit eMedicine''s Back, Ribs, Neck, and Head Center. Also, see eMedicine''s patient education article Concussion.
Pathophysiology
Brain
contusions commonly are identified in patients with traumatic
brain injury (TBI) and represent regions of primary neuronal and
vascular injury. These edematous lesions contain punctate parenchymal
hemorrhages, which are termed microhemorrhages. By definition these
parenchymal bruises are found on the surfaces of the brain. Blood may
extend bidirectionally into the white matter and the subdural and
subarachnoid spaces.
Contusions are formed in 2 ways: direct trauma and
acceleration/deceleration injury. Direct trauma causes injury at the
site of impact, which is termed a coup contusion, while deceleration
causes injury at a site opposite to the site of impact, which is termed
a contrecoup contusion.
In the first mechanism, direct trauma, the head is not in motion. This mechanism may result in a scalp or skull injury.
The second mechanism is related to acceleration (eg, boxing injury)
or deceleration (eg, motor vehicle accident), which causes the brain to
strike the skull. In an event in which the head is in motion, cortical
injury occurs adjacent to the floor of the anterior or posterior
cranial fossa, the sphenoid wing, the petrous ridge, the convexity of
the skull, and the falx or tentorium. The inferior frontal and temporal
lobes are particularly vulnerable.
Gliding contusions are due to sagittal angular acceleration with
abrupt stretching and tearing of the parasagittal veins, arachnoid
membrane, and adjacent cerebrum. Gliding contusions occur along the
superior margin of the cerebral hemispheres. Sganzerla et al concluded
that the gliding
contusion should be considered another type of primary
brain damage brought about by acceleration/deceleration shear strains.
Therefore, these authors believe that a patient with a gliding
contusion will most likely have diffuse axonal injury as well.
Contusions may progress with time. CT scans often demonstrate
progression over time in the size and number of contusions and the
amount of hemorrhage within the contusions. Such changes are most
evident over the first 24-48 hours, with one fourth of
cases demonstrating delayed hemorrhage in areas that were previously free of
hemorrhage.
Frequency
United States
Variations in the reported incidence may be due to different data
collection methods and the diversity of the populations studied. Each
year, TBI occurs in more than 800,000 people in the United States.
Although 90% of patients survive the injury, 25% or more have
significant residual complaints.2
The National Institutes of Health (NIH) Consensus Statement 1998
estimates that 1.5-2 million Americans have a TBI each year, or an
annual incidence of 100 cases per 100,000 persons.3 The
National Health Interview Survey (NHIS) estimates that 1.5-2 million
people have a TBI each year in the United States. Approximately 1
million of these individuals are treated in hospital emergency
departments (EDs). Using self-reported data from the 1991 NHIS Injury
Supplement (NHIS-I), Sosin et al estimated that 1.5 million persons had
TBIs in 1991.4
Among these, 35% (525,000, or 216 cases per 100,000 population)
received medical attention in EDs and were not admitted to the hospital.
Mortality/Morbidity
Mortality: In 1994, more than 147,500 Americans died of
traumatic injury. This figure represents approximately 6.5% of all
deaths in the United States. The exact
Mortality rate involving
significant TBI is not known, and estimates of mortality rates vary.
The reported TBI mortality rate varies from 14-30 cases per 100,000
population. Thurman et al estimate the 1994 incidence rate of
fatalities and hospital admissions in patients with TBIs was 91 cases
per 100,000 population.5 Annegers et al note that the elderly population has the highest mortality rate.6 However, Woo et al note that the mortality rates for TBI are highest in persons aged 15-24 years.
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