<unk>  (SIS) occurs when the brain swells rapidly, and catastrophically, after a person suffers a<unk>  concussion before symptoms from an earlier one have subsided. This<unk>  blow may occur minutes, days or weeks after an initial concussion, and even the mildest grade of concussion can lead to<unk> . The condition is often fatal, and almost everyone who is not killed is severely disabled. The cause of SIS is uncertain, but it is thought that the brain's arterioles lose their ability to regulate their diameter, and therefore lose control over cerebral blood flow, causing massive cerebral edema. Most cases of SIS have occurred in children, who are thought to be particularly vulnerable. In order to prevent SIS, guidelines have been established to prohibit athletes from returning to a game prematurely. For example, professionals recommend that athletes not return to play before symptoms of an initial head injury have resolved.
Second-impact syndrome
Post-intensive care syndrome
Sandifer syndrome
Tumor lysis syndrome
Overlap syndrome
Majeed syndrome
Compartment syndrome
Edwards syndrome