[Severe Traumatic Brain Injury due to Repeated Minor Head Injury while Snowboarding:A Report of Two Cases].

Second impact syndrome occurrs when a patient who has sustained an initial head injury, most often a concussion, sustains a second head injury before the symptoms associated with the first have fully resolved, leading to rapid brain swelling and herniation. However, the underlying pathophysiology remains unclear. We report two cases in which acute subdural hematoma with rapid malignant brain swelling developed after repeated head traumas while snowboarding. One patient did not undergo craniotomy and died 21h after symptom onset. The other underwent urgent decompressive craniotomy and experienced prolonged disturbance of consciousness. Axial susceptibility-weighted magnetic resonance imaging performed 1 month after surgery in the second patient revealed multiple microbleeds in the subcortical white matter and parasagittal white matter in the bilateral hemispheres. These findings indicate that axonal injuries from angular acceleration may contribute to the rapid malignant brain swelling and poor outcomes.