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Traumatic Brain Injury: Causes, Mechanisms, and Classification

TBI results from external mechanical force causing brain dysfunction. Severity: mild (concussion), moderate, severe (GCS-based).

Mechanisms of Injury

  1. Blunt impact (contact): Coup-contrecoup, skull fracture, intracranial hemorrhage (epidural, subdural, subarachnoid, intraparenchymal). Most common (falls, MVC, assault).
  2. Penetrating: Missile (bullet), fragment, implement. Direct tissue destruction + cavitation. Higher mortality.
  3. Blast/Explosion: Primary (shock wave), secondary (fragments), tertiary (body displacement), quaternary (burns, toxins). Military + industrial.
  4. Acceleration-deceleration (inertial): Diffuse axonal injury (DAI) from shear-strain of white matter tracts. MVC, shaken baby.
  5. Sports-related: Concussion, subconcussive hits → CTE risk. Helmet reduces skull fracture, not DAI.
  6. Child abuse: Abusive head trauma (shaken impact syndrome). Retinal hemorrhages, rib fractures.

Secondary Injury

Excitotoxicity, oxidative stress, inflammation, edema, ischemia, mitochondrial failure → evolves over hours-days. Target for neuroprotection.

Classification

  • GCS 13–15: Mild (concussion).
  • GCS 9–12: Moderate.
  • GCS 3–8: Severe.
  • Structural: Focal (hematoma, contusion) vs. Diffuse (DAI, edema).

Early resuscitation (ABCs, CPP >60), ICP monitoring, surgical decompression, rehabilitation.

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