Table 1 Head trauma terminology

Traumatic Brain Injury (TBI)

Symptomatic injury often requiring presence of either loss of consciousness (LOC) or posttraumatic amnesia (PTA)

Crudely delineated as “mild,” “moderate,” or “severe” based on duration of LOC or PTA or using Glasgow Coma Scale score

More commonly applied in studies of civilian populations in emergency department settings or military servicemembers and veterans than in sport-related head trauma settings

Concussion

Symptomatic injury often considered interchangeable with “mild TBI”

In sport settings, concussion diagnoses frequently are made without documented LOC or PTA, but based on presence of other head trauma-associated symptoms like headache, dizziness, poor balance, nausea, or eye movement abnormalities, among others

Instances of “getting your bell rung,” “seeing stars,” or “clearing the cobwebs” typically qualify for a concussion diagnosis

Subconcussive Trauma

Asymptomatic head impacts usually occurring in the context of collision sports

In collision sports like American football, athletes may sustain tens of thousands of asymptomatic, subconcussive head impacts in the course of an extended playing career

In military settings, servicemembers may experience subconcussive exposure in the form of repeated blast exposures or training activities (e.g., breacher or combat training) without associated acute clinical symptoms

Traumatic Encephalopathy Syndrome (TES)

Research criteria proposed for classifying cognitive and neurobehavioral symptoms believed to be associated with repetitive head trauma and with onset typically years after last head trauma exposure

TES diagnostic criteria have high sensitivity but low specificity to underlying CTE neuropathology

In this review, “TES” refers to study populations defined by clinical symptomatology in the context of prior repetitive head trauma, without presumption of underlying CTE neuropathology

Chronic Traumatic Encephalopathy (CTE)

Neuropathologic changes found in the brain per consensus diagnostic criteria (phosphorylated tau protein aggregates in neurons around blood vessels at the depths of cortical sulci)

CTE diagnosis is made independent of patient symptoms during life

In this review, “CTE” refers only to study populations with autopsy-confirmed evidence of CTE neuropathology