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
Recovery
Plasticity
- Neuronal regeneration/collateral sprouting
- Functional/neural reorganization/unmasking
Diaschisis
- 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
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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.