To report a case of second impact syndrome (SIS) in an adult male and summarize the literature of SIS in adults.

Second impact syndrome (SIS) is a catastrophic consequence of repeated mild-head injury, characterized by malignant generalized cerebral edema. The documented cases of SIS in literature are scarce, and most are limited to adolescent population.

A 31-year-old male presented after collapsing while experiencing two blows to his head while boxing. At presentation, he was in comatose state without discernible brainstem reflexes. Initial head CT showed thin subdural hematoma, transtentorial herniation and extensive cerebral edema out of portion to the hemorrhage. Intracranial pressure (ICP) monitor showed an initial value of 54 mmHg and brain parenchymal oxygen tension (Pbto2) of 7.4 mmHg. The ICP and Pbto2 remained refractory to escalating tiers of management An inquest revealed the patient had sustained an initial head insult during a fight two weeks prior, whereafter, he had headaches, irritability and lethargy suggestive of a post-concussive state. The patient ultimately demised secondary to cardiac arrest. He was turned over to the medical examiner for autopsy, the results of which are still pending.

Literature search revealed 15 adult cases of SIS with onset age ranging from 18-29. All the cases exclusively happened in male population and 10 died after the injury. Interval time of the recurrent head injuries varies from 1-35 days, with the majority of the cases reporting a delayed onset time when compared to pediatric cases.

SIS is a rare but devastating condition which may be under reported in adults. Management of sport related head injuries and return to play guidelines continue to be challenging. Given the delayed occurrence, physician awareness on the occurrence of SIS in adults while providing return-to-play advice is crucial.