The relative risk of<unk>  increases with the severity of injury. As age increases, risk of early and late<unk> s decreases. Research has found that the incidence of<unk>  varies widely based on the population studied; it may be as low as 4.4% or as high as 53%. Of all TBI patients who are hospitalized, 5 to 7% have<unk> .<unk>  occur in about 3.1% of<unk>  brain injuries, but the severity of injury affects the likelihood of occurrence. The most important factor in whether a person will develop early and late<unk> s is the extent of the damage to the brain. More severe brain injury also confers a risk for developing<unk>  for a longer time after the event. One study found that the probability that<unk> s will occur within 5 years of injury is in 0.5% of mild<unk>  brain injuries (defined as no skull fracture and less than 30 minutes of<unk><unk>  amnesia, abbreviated PTA, or loss of consciousness, abbreviated LOC); 1.2% of moderate injuries (skull fracture or PTA or LOC lasting between 30 minutes and 24 hours); and 10.0% of severe injuries (cerebral contusion, intracranial hematoma, or LOC or PTA for over 24 hours). Another study found that the risk of<unk> s 5 years after TBI is 1.5% in mild (defined as PTA or LOC for less than 30 minutes), 2.9% in moderate (LOC lasting between 30 minutes and 1 day), and 17.2% in severe TBI (cerebral contusion, subdural hematoma, or LOC for over a day; image at right). Immediate<unk> s have an incidence of 1 to 4%, that of early<unk> s is 4 to 25%, and that of late<unk> s is 9 to 42%. Age influences the risk for<unk> . As age increases, risk of early and late<unk> s decreases; one study found that early<unk>  occurred in 30.8% of children age 7 or under, 20% of children between ages 8 and 16, and 8.4% of people who were over 16 at the time they were injured (graph at right). Early<unk> s occur up to twice as frequently in brain injured children as they do in their adult counterparts. In one study, children under five with trivial brain injuries (those with no LOC, no PTA, no depressed skull fracture, and no hemorrhage) suffered an early<unk>  17% of the time, while people over age 5 did so only 2% of the time. Children under age five also have<unk> s within one hour of injury more often than adults do. One study found the incidence of early<unk> s to be highest among infants younger than one year and particularly high among those who suffered perinatal injury. However, adults are at higher risk than children are for late<unk> s. People over age 65 are also at greater risk for developing<unk>  after an injury, with a<unk>  risk that is 2.5 times higher than that of their younger counterparts. Risk factors The chances that a person will suffer<unk>  are influenced by factors involving the injury and the person. The largest risks for<unk>  are having an altered level of consciousness for a protracted time after the injury, severe injuries with focal lesions, and fractures. The single largest risk for<unk>  is penetrating head trauma, which carries a 35 to 50% risk of<unk> s within 15 years. If a fragment of metal remains within the skull after injury, the risk of both early and late<unk>  may be increased. Head trauma survivors who abused alcohol before the injury are also at higher risk for developing<unk> s. Occurrence of<unk> s varies widely even among people with similar injuries. It is not known whether genetics play a role in<unk>  risk. Studies have had conflicting results with regard to the question of whether people with<unk>  are more likely to have family members with<unk> s, which would suggest a genetic role in<unk> . Most studies have found that epilepsy in family members does not significantly increase the risk of<unk> . People with the ApoE-ε4 allele may also be at higher risk for late<unk> . Risks for late<unk>  include hydrocephalus, reduced blood flow to the temporal lobes of the brain, brain contusions, subdural hematomas, a torn dura mater, and focal neurological deficits. PTA that lasts for longer than 24 hours after the injury is a risk factor for both early and late<unk> . Up to 86% of people who have one late<unk>  have another within two years. <!--
Post-traumatic seizure
Musicogenic seizure
Reflex seizure
Post-traumatic epilepsy
Febrile seizure
Non-epileptic seizure
Musicogenic epilepsy
Transient ischemic attack