flected in delays in reaching developmental mi lestones (e.g., language acquisition), worse
academic performance, and possibly impaired  social development. Among older teenag-
ers and adults, persisting symptoms may incl ude various neurocognitive deficits, irrita-
bility, hypersensitivity to light and sound, e asy fatigability, and mood changes, including
depression, anxiety, hostility, or apathy. In older individuals with depleted cognitive re-
serve, mild TBI is more  likely to result in incomplete recoveries.
Risk and Prognostic Factors 
Risk factors for traumatic brain injury. Traumatic brain injury rates vary by age, with
the highest prevalence among individuals younge r than 4 years, older adolescents, and in-
dividuals older than 65 years. Falls are the mo st common cause of TBI, with motor vehicle
accidents being second. Sports concussions are frequent causes of TBI in older children,
teenagers, and young adults.
Risk factors for neurocognitive disorder after traumatic brain injury. Repeated con-
cussions can lead to persistent NCD and neur opathological evidence of traumatic enceph-
alopathy. Co-occurring intoxication with a substance may incr ease the severity of a TBI
from a motor vehicle accident, but whether into xication at the time of injury worsens neu-
rocognitive outcome is unknown.
Course modifiers. Mild TBI generally resolves within a few weeks to months, although res-
olution may be delayed or incomplete in the context of repeated TB I. Worse outcome fromTABLE 2 Severity ratings for tr aumatic brain injury
Injury characteristic Mild TBI Moderate TBI Severe TBI
Loss of consciousness <30 min 30 minutes–24 hours >24 hours
Posttraumatic amnesia <24 ho urs 24 hours–7 days >7 days