Does Second Impact Syndrome Exist?

Abstract

  The first clinical description of second impact syndrome (SIS) was provided by Bollinger (1881). Schneider (1973) updated this condition. The term SIS was first used by Saunders (1984). Saunders (1984) defined it as a catastrophic brain injury following a minor impact. An initial minor head injury is often diagnosed as a concussion. After 0-30 days (average 1-2 weeks), the patient suffers a second trauma and develops a serious condition. A second trauma is often less severe than a single trauma that could cause fatal brain damage. One possible mechanism underlying SIS is acute cerebral swelling due to impaired cerebrovascular autoregulation. Most cases are reportedly associated with acute subdural hematomas, suggesting that these may be the true pathology of SIS. The unique presentation scheme of the SIS was insufficient to support a standardized WHO case definition ; however, the pathogenesis remains unclear. Severe head trauma with diffuse brain swelling can occur following minor injuries. Currently, the SIS expresses only one concept and should not be feasible for diagnosis. In all operated-on or autopsied SIS cases, the volume of the acute subdural hematoma was low and was not considered to be a cause of brain swelling. Whether fatal brain swelling is due to dysautoregulation, vasogenic edema, venous insufficiency, cortical spreading depolarization, trigeminocardiac reflex, or a combination of some or all of these remains disputable. If SIS occurs, there is nothing to do. The only way to prevent SIS is to ensure its nonoccurrence. This study aimed to clarify whether the fatal cerebral swelling associated with repeated sports-related concussions (SRC) should be classified as SIS or “post-traumatic diffuse cerebral swelling.” Further, regardless of its specific designation, this study will explore whether the underlying mechanism impacting this condition ultimately alters the essential principles of managing SRC and the criticality of implementing a graduated return-to-play protocol. Because some National Federations of the Japanese Olympic Committee and lecture materials for sports instructors refer to SIS, the mechanism of this phenomenon requires clarification from neurosurgeons.