Brain Injury, Traumatic

Descriptive text is not available for this imageBASICS

DESCRIPTION

  • Traumatic brain injury (TBI): alteration in brain function or other evidence of brain pathology, caused by an external force
  • It is classified as mild, moderate, or severe according to injury characteristics that suggest extent of damage to the brain.
  • A Glasgow Coma Scale (GCS) score of 13 to 15 is considered mild injury, 9 to 12 is considered moderate injury, and ≤8 is considered severe TBI.
  • For information regarding mild TBI, please refer to the “Concussion” chapter.
  • Moderate or severe TBI is caused by a blunt force to the head or impact from a penetrating injury (i.e., gunshot) to the head.

EPIDEMIOLOGY

  • Pediatric TBI
    • 16,480 TBI-related hospitalizations in 2018
    • 2,476 TBI-related deaths in 2019
    • Almost 500,000 emergency department (ED) visits each year for TBI for those aged 0 to 14 years
    • Males 0 to 4 years of age had the highest rate of TBI ED visits.
  • 75% of TBIs each year are mild.
  • <2 years old: Nonaccidental trauma is the principal cause of TBI.
  • >2 years old: Falls (around 37%) are most common cause of trauma.
  • For severe TBI, nonaccidental trauma remains the principal cause in young children.
  • Motor vehicle accidents are most common cause of TBI in older children, although penetrating injuries are becoming more common.

PATHOPHYSIOLOGY

  • Primary brain injury: mechanical forces during initial insult
    • Focal or diffuse injuries
    • Focally applied forces: lacerations, penetration injuries, skull fractures
    • Focal cerebral contusions are common in the basal frontal and temporal areas.
    • Diffuse brain injury is caused by noncontact forces of rapid deceleration and acceleration which cause shearing and stretching injury in cerebral brain tissues.
    • Shearing mechanisms may lead to diffuse axonal injury (DAI)
      • DAI can be seen on imaging as multiple small lesions within the white matter tracts.
      • DAI usually has poor outcome and accounts for approximately 70% of moderate to severe TBI cases.
    • The hallmark feature of diffuse TBI is extensive damage of axons predominantly in subcortical and deep white matter tissue such as the brain stem and corpus callosum.
    • Extra-axial hematomas occur when forces affect the most superficial cerebral layers and include epidural, subdural, and subarachnoid hemorrhage.
  • Secondary brain injury: molecular injury mechanisms that continue after initial trauma
    • Factors that contribute to secondary injuries include excitotoxicity, mitochondrial dysfunction, oxidative stress, lipid peroxidation, neuroinflammation, axon degeneration, and apoptotic cell death.
    • In severe TBI, CT or MRI signs of edema may progress over 3 to 5 days (see “Treatment”).
  • Age-specific pathophysiology:
    • Infants/toddler
      • Shearing forces on the brain due to acceleration/deceleration avulse axons from their cell bodies causing DAI; often compounded by tearing and bleeding of dural veins
      • Unmyelinated infant brain absorbs rather than transfers impact. Immature, distensible skull renders brain less likely to contuse or herniated but more likely to sustain diffuse secondary injuries, with swelling.
      • Subgaleal hematoma, cephalohematoma (below the periosteum), and caput succedaneum (confined to the superficial scalp) at birth do not predict brain injury.
      • More severe birth trauma can result in subdural hematoma (SDH).
      • Bilateral interhemispheric SDH suggests nonaccidental trauma.
      • Diffuse injuries secondary to shaken impact syndrome can lead to cerebral swelling with secondary infarction and/or decreased central respiratory control, leading to apnea, hypoxia, seizures, and cerebral edema.
      • Suspect nonaccidental trauma with growing skull fracture, if >1 cranial bone involved or if other injuries are present, such as retinal hemorrhages or other fractures.
    • Older children/adolescents
      • Still more subject to DAI than adults due to incomplete myelination
      • Projectile injuries in adolescent population may cause prolonged brain swelling (particularly close-range gunshot wounds).

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