Blunt impact to the head that deforms the skull causes transmission of a pressure wave through the brain that results in abrupt and transient cavitation in brain tissue. Mechanical forces propagate a pressure wave through the brain.38,49Mechanical forces of head injury cause the brain to accelerate with induction of rotation and shearing injury to fiber tracts and blood vessels and contusion.50 Contusion results in hemorrhage, with an admixture of red blood cells, necrotic brain caused by coagulation necrosis, and edema caused by mechanical disruption of blood vessels or by cellular diapedesis.

Histopathologic studies of material obtained from traumatized brain show:51–53

  • formation of axonal retraction balls
  • reactive gliosis
  • wallerian degeneration
  • microglial star formation within cystic white matter lesions

Mechanical effects cause bulk displacement of tissue with secondary responses that include alterations in cerebral vasomotor regulation, vasospasm, altered cerebral blood flow, changes in intracranial pressure, and altered vascular permeability.54

Delayed effects of acute head trauma include focal or diffuse brain edema, ischemia, necrosis, gliosis, and neuronal loss.

Adapted from: Willmore LJ. Head trauma and the development of post-traumatic epilepsy. In: Ettinger AB and Devinsky O, eds. Managing epilepsy and co-existing disorders. Boston: Butterworth-Heinemann; 2002;229–238.
With permission from Elsevier (www.elsevier.com).

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Reviewed By: 
Steven C. Schachter, MD
on: 
Thursday, April 1, 2004