II. Definitions

  1. Second Impact Syndrome
    1. Following a first Minor Head Injury, a second significant Head Injury results in severe neurologic injury

III. Epidemiology

  1. Uncommon to rare, but with devastating consequences
  2. Appears limited to children and adolescents
    1. Although adults with multiple Concussions may develop chronic Traumatic encephalopathy (CTE)
    2. CTE, by contrast, results in a chronic neurodegenerative disorder with Dementia and Parkinsonism features

IV. Pathophysiology

  1. Results from repeated Concussions over a short period of time
    1. Initial Traumatic Brain Injury initiates an inflammatory response and altered cerebral autoregulation
  2. Subsequent head injuries result in cerebral edema without physiologic compensatory mechanisms
    1. Rapid and diffuse cerebral edema with no effective treatment (does not respond to manitol)
    2. Reduced cerebral Blood Flow or fluctuating cerebral flow, varying with systemic perfusion

V. Signs

  1. Rapid neurologic decline following repeated Head Injury

VI. Imaging

  1. CT Head
    1. Cerebral edema
    2. Small Cerebral Ventricles
    3. Loss of cerebral sulci
    4. Loss of subarachnoid space

VIII. Prevention

  1. Helmets should not offer a false sense of security against Second Impact Syndrome
    1. Helmets do not prevent Second Impact Syndrome in those with unresolved prior Concussion-related symptoms
  2. Prevention of Second Impact Syndrome is the primary focus of post-Concussion guidelines in sports
    1. See Return to Play after Concussion

IX. Course

  1. Mortality approaches 50% with severe neurologic sequelae in the other 50%

X. References

  1. Dreis (2020) Crit Dec Emerg Med 34(7):3-21
  2. McCrory (2012) Br J Sports Med 47(5): 250-8 [PubMed]

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