Routine CT imaging may not show the extent of derangement of an initial head impact injury and a normal head CT does not preclude the need for close clinical follow-up after head injury, according to a case report of second impact syndrome (SIS), published Jan. 1 in Journal of Neurosurgery: Pediatrics.

SIS is a rare, often fatal, head injury that occurs when a second head injury is sustained before symptoms of an earlier head injury have resolved. Elizabeth Weinstein, MD, from the department of emergency medicine at Indiana University School of Medicine in Indianapolis, and colleagues presented the clinical and imaging history of a patient with SIS on whom a head CT was performed after the first impact and early brain MRI after the second impact.

The patient, a 17-year old high school football player, reported fatigue and headache for three days after a helmet-to-helmet hit. A head CT, obtained four days after the injury, was interpreted as normal at the initial review and on subsequent review by several neurosurgeons and a neuroradiologist.

Although the patient was instructed to refrain from practice until his symptoms resolved, he returned to practice five days after the injury and sustained a second hit. He was slow to get up and shortly after became unresponsive. At that point, a head CT demonstrated thin bilateral hematomas. Subdural hematomas and mild cerebral swelling were present on repeat CT imaging.

MRI imaging revealed mild downward transtentorial herniation, bilateral subdural hematomas and abnormal T2 signal and restricted diffusion in the medial left thalamus and hypothalamus. The MR study also showed caudal displacement of the thalamus and hypothalamus.

The case, according to Weinstein and colleagues, suggests the initial impact results in derangement at a level not visible on routine CT scanning. “Importantly, this case shows that a normal head CT scan does not obviate the need for close clinical follow-up and for the athlete to be cognitively normal and asymptomatic before return to play.”

The imaging findings support the model in which cerebral blood flow dysautoregulation results in massive hyperemia that may result in fatal or near-fatal hyperemic herniation of the brain.

Weinstein and colleagues acknowledged that it remains unclear why one player suffers SIS, but clarified that younger players seem to be at greater risk than older players.

The current case report may identify patients at risk for SIS. Specifically, the persistence, duration and severity of the patient’s headache indicate significant ongoing neurophysiological pathology despite normal CT results. It is possible, according to the researchers, that the patient's severe headache may have represented mild intracranial hypertension from hyperemia after the first head injury.

Decisions about return to play for the 300,000 athletes who suffer traumatic brain injuries annually in the U.S. must take into account the rare occurrence of SIS and sudden death. “It is imperative that physicians familiar with sports concussions take the lead in educating coaches, athletes, families and primary care and emergency physicians about sports-related head injuries and their potential risks and consequences.”