Sport-Related Mild Traumatic Brain Injury

This discussion will address new advances in mTBI management and return-to-play decisions for adolescent athletes in the primary care setting.

TERMINOLOGY AND PATHOPHYSIOLOGY
The terminology associated with mTBI has been evolving along with an enhanced understanding of its pathology and etiology. Since more than 90% of sport-related traumatic brain injuries (TBIs) are considered “mild,” the term mTBI is often being used in place of concussion.¹⁴ Considering the long-lasting effects of more severe TBI, the contemporary term mTBI more accurately portrays the seriousness of even a seemingly minor injury, often minimized as a “ding” or “bell ringer.” These lay terms do not convey the magnitude and extent of injury sustained and are often thought by nonmedical persons to refer to a different, unrelated injury.⁶

Since the Concussion in Sport Group¹⁸ first met in 2001, several features of sport-related mTBI have been described in an effort to clarify its definition. These include an injury that

(1) is caused by a direct blow to the head or an indirect blow elsewhere in the body that transmits an impulsive force to the head

(2) may cause an immediate and short-lived alteration in neurologic function

(3) may cause neuropathologic changes but typically reflects a functional disturbance rather than a structural injury

(4) is represented by a gradient of clinical symptoms that often resolve sequentially, often without loss of consciousness

(5) is predominantly associated with negative findings on conventional neuroimaging studies (eg, CT, MRI).¹⁸

When an athlete sustains an impact to the head, external forces create accelerations and decelerations of the brain within the skull. These forces create the classic coup-contrecoup injury,¹ in which the brain impacts the skull at the initial point of contact, with a second point of injury on the directly opposite side of the brain. In some cases, rotational forces occur when the skull is impacted in such a way that the brain rotates about its axis, causing shear and stretch forces on the brain tissue. Either mechanism of injury can trigger a chain of metabolic events in the brain that result in decreased blood flow, increased glucose utilization, and neurotransmitter dysfunction. All of these are thought to contribute to the transient neurologic deficits associated with mTBI.^21,22

If a patient who is recovering from mTBI sustains a second head injury before metabolic changes caused by the first injury have fully resolved, a second-impact syndrome (SIS)^12,13,16 can develop (see Figure 1^12,13,16 ). SIS results in massive, rapid brain edema, causing increased intracranial pressure and eventual brain herniation. The majority of cases of SIS are reported in patients younger than 18 and are thought to be the result of altered autoregulation of cerebral blood flow.¹² In pediatric athletes, therefore, the proper recognition of mTBI, its effective management, and the return-to-play determination are crucial to decrease the risk of SIS.

INITIAL EVALUATION
The clinical course and management of mTBI can be separated into two distinct components.²³ The first is the initial or acute evaluation, which should occur as close to the time of injury as possible. Evaluation of an acute mTBI centers on the history and physical examination at the time of injury; its focus is to determine whether a neurosurgical emergency exists and what course of treatment is needed. Tools such as the Standard Assessment of Concussion (SAC)²⁴ and Folstein’s Mini–Mental State Examination (MMSE)²⁵ should be used to assess the extent of initial cognitive impairment, while other tools, such as the Balance Error Scoring System²⁶ test for motor impairment, should be combined with the neurologic physical exam to formulate the differential diagnosis.

No two brain injuries are alike. The clinician must key into the mechanism of injury, initial and current symptoms (including headache, confusion, and amnesia),¹⁶ and positive and negative neurologic findings. Differentials that must be ruled out immediately include skull fracture, cerebral contusion, and epidural hematomas.

Along with the physical findings associated with mTBI, those suggesting more severe injury may include acute localized swelling, deformity, prolonged loss of consciousness, intractable vomiting, and often multiple positive neurologic exam findings, such as cranial nerve abnormalities and motor weakness. Any one of these findings in the initial evaluation warrants activation of emergency medical services, including immediate transport to an ED equipped to manage a neurosurgical emergency.

Since 1974, at least 25 different scales have been used to help practitioners evaluating mTBI assign a grade of severity.¹ Although grading scales can be helpful to objectify subjective symptoms, they vary considerably, and none has been shown valid, reliable, or sensitive through published research. Furthermore, an assigned grade cannot reliably express the severity of injury or the prognosis for recovery in each case.^1,17