Second-Impact Syndrome

Second-impact syndrome (SIS) has been documented in multiple reports but remains a hotly debated diagnosis. In a series of publications in World Neurosurgery, leaders in the field continue to debate SIS and its management and prevention.

SIS occurs primarily in adolescent athletes who have a second concussion while still symptomatic from the first concussion. It is characterized by loss of consciousness and, in its most severe form, may lead to death within minutes following the second concussion.

In a recent report, Yokota and Ida describe a case of 16-year-old judo athlete who sustained two blows to the head.¹ Despite developing an acute subdural hematoma, which was visible on computed tomography (CT) but overlooked, the patient was allowed to return to practice. After sustaining the second blow 19 days later, he lost consciousness and developed convulsions. The second CT revealed another hematoma. Following emergency surgery, the patient recovered.

This report has evoked an enthusiastic response in the form of three commentaries from concussion management experts, who commented on pathophysiology of SIS, management of athletes after the second impact, and existing guidelines on prevention of repeated concussions in young athletes.

First, pathophysiology of SIS is not entirely clear. It is speculated that brain swelling observed during SIS is related to either dysregulation of cerebral vasculature or subdural hematoma. As Leonidas Quintana explains in one of the commentaries, compensatory changes in cerebral blood flow after the first impact may be the pathophysiologic foundation of SIS.² Brain swelling produced by the first impact triggers a series of events, making the brain lose its ability to autoregulate its blood flow. In this altered state, the brain is especially vulnerable to another impact. If a second impact occurs, uncontrolled brain swelling will ensue, resulting in brain herniation, brainstem compromise, respiratory failure, and in severe cases, death.

The role of subdural hematoma in pathophysiology of SIS is controversial; opinions in favor and against its causative role in brain swelling exist. According to Robert Cantu, the author of another commentary, acceleration/deceleration forces during an impact can cause both brain swelling and hematoma, the latter requiring greater forces than the former.³ Thus, in cases similar to that described above, the presence of hematoma implies the presence of SIS; however, SIS may arise in the absence of hematoma as well.

Second, management of athletes after the second impact is debated. Cantu declares CT a “study of choice” because of its ability to detect hemispheric enlargement, midline shift and hemorrhage, and to accommodate life-support equipment that accompanies these patients. Indeed, CT was used in evaluation of the judo athlete described above. Quintana, however, notes that classic SIS results in death within minutes and questions value of CT in this setting. Immediate interventions in the field, such as rapid intubation and administration of mannitol or hypertonic saline, may prove more valuable; in the meantime, their effectiveness remains unclear.

Third, guidelines and measures developed in the US and their limitations is the focus of another commentary, by Zusman and colleagues.⁴ Thanks to general guidelines on concussion management, sport-specific guidelines, and legislative measures, athletes playing popular sports (hockey, soccer, and football) in the US receive superior education and safety. These measures should inspire efforts to fill many gaps still existing in less popular sports in the US and overseas (wrestling, judo). Quality of and access to concussion care can also be improved through collaboration of academic and community centers.

In conclusion, SIS remains a controversial diagnosis, leaving much room for research and discussion. Unlike its pathophysiology, the need for better management and prevention is clear. Positive examples of preventative and care measures exist in the US and should be adopted broadly.

References:

1. Yokota H, Ida Y. Acute subdural hematoma in a judo player with repeated head injuries. World Neurosurg. 2016 Jul;91:671.

2. Quintana LM. Second impact syndrome in sports. World Neurosurg. 2016 Jul;91:647-649.

3. Cantu RC. Dysautoregulation/second impact syndrome with recurrent athletic head injury. World Neurosurg. 2016 Apr 22. [Epub ahead of print]

4. Zusman EE, et al. Can ideas from United States youth sports reduce judo-related head injuries in Japan? World Neurosurg. 2016 Jun 8. [Epub ahead of print]