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Second Impact Syndrome


KEY FACTS

Terminology

  • Dysautoregulation/second impact syndrome

  • Repeated head trauma within “window of vulnerability” before brain recovers from initial concussive injury

  • May cause catastrophic brain swelling

Imaging

  • Thin, acute subdural hematoma (aSDH)

    • Disproportionate mass effect

      • –

        Midline (subfalcine) shift more than accounted for by thickness of aSDH

  • Swollen, hypodense cerebral hemisphere under aSDH

    • Underlying sulci compressed, then obliterated

  • Best imaging tools

    • NECT (initial screening) ± MR with T2*, DWI

Top Differential Diagnoses

  • aSDH (without underlying dysautoregulation)

  • Nonaccidental trauma (child abuse)

Pathology

  • Thin subdural hematoma

  • Underlying brain swollen, hyperemic

    • May represent excitotoxic injury

    • ± secondary infarcts

    • ± uncal, central, tonsillar herniations

Clinical Issues

  • Severe headache

  • Vomiting

  • May have dramatic, sudden collapse, coma

  • Most common in

    • Adolescent male patients involved in high-impact sports

    • Abused infants

    • Elderly patients with repeated falls, head impacts

Axial NECT in an abused infant with repeated inflicted head trauma shows a mixed-density right subdural hematoma (SDH)
. The underlying right hemisphere is diffusely swollen and hypodense. Note disproportionate mass effect, subfalcine herniation
compared with relatively thin SDH.

Axial NECT in an elderly patient with repeated falls and head trauma shows a thin acute SDH
. Underlying cortex is swollen
with disproportionate mass effect on left lateral ventricle.

Axial NECT in an abused infant shows mixed acute, subacute/chronic SDH overlying a swollen, hypodense hemisphere.

Axial fat-suppressed T2WI in the same case 2 days later, after evacuation of the SDH, shows swollen hyperintense cortex
underlying bilateral SDHs. Note hyperintensity in the corpus callosum splenium
. Findings are consistent with excitotoxic injury.

TERMINOLOGY

Abbreviations

  • Second impact syndrome (SIS)

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