Primary vs. Secondary Injury

Primary injury

  • Contusions → bruising of cortical tissue
  • Diffuse axonal injury → shearing from accel/deceleration and rotational forces; white matter petechial hemorrhages

Secondary injury

  • Excitotoxicity → neuronal damage 2/2 massive surge in neurotransmitters
  • Brain swelling → early increase in cerebral blood volume
  • Brain edema → later increase in cerebral water volume (vaso/cytogenic)
Focal versus Diffuse Injury

Focal injury

  • EDH → skull fracture, temporal bone, middle meningeal artery, lucid interval
  • SDH → shearing of bridging veins between pia-arachnoid and dura
  • SAH → ruptured cerebral aneurysms, arteriovenous malformations

Diffuse injury

  • Grade 1: widespread white matter/axonal damage, no focal findings on imaging
  • Grade 2: widespread damage, focal findings (usually in corpus callosum)
  • Grade 3: damage involving the brainstem


  • Neuronal regeneration/collateral sprouting
  • Functional/neural reorganization/unmasking


  • Spontaneous return of function
  • Injury to site A inhibits function at site B (which is not injured) via fiber tract connections, recovery of functions controlled by B parallels recovery of site A
  • References

    Elovic E, Baerga E, Galang GF, Cuccurullo SJ, Reyna M, Malone RJ. Physical Medicine and Rehabilitation Board Review. 3rd ed. New York, NY: Demos Medical; 2015. Chapter 2, Traumatic Brain Injury. P.96-146.

    Feeney DM. Pharmacologic modulation of recovery after brain injury: a reconsideration of diaschisis. J Neurol Rehabil. 1991;5:113–128.