According to the research young children who sustain a severe head injury around ages 3 to 7 are three and a half times more likely to develop attention deficit hyperactivity disorder (ADHD)  as they grow older

"Children had a risk of developing attention problems after recovery from brain injury," said lead researcher Megan Narad. "By that point, I think a lot of people consider these kids recovered from their injury, but there's a chance they could be developing some new problems later on," said Narad, a psychology fellow at Cincinnati Children's Hospital.

Prior research has shown that kids with severe head injuries are more likely to have attention problems following their injury. In fact, ADHD is the most common psychiatric disorder among children with a history of severe brain injury.

But up to now, the longest-term studies have only followed children for around two years. This study tracked 81 brain-injured kids an average of seven years, "when they're getting ready to go to middle school and are considered to have recovered from their injury," Narad said.

Researchers followed up with the youngsters to see if they developed symptoms of ADHD by the time they entered middle school. The investigators also compared them with a control group of 106 children who had been hospitalized around the same time for an orthopedic injury.

Out of the total 187 kids followed in this study, 48 more than one-quarter were diagnosed by researchers as having ADHD. Children who had sustained the most severe traumatic brain injuries were 3.6 times more likely to develop ADHD, compared with the control group, results showed. On the other hand, kids with mild or moderate brain injury did not differ significantly from the control group.

"Follow-up after significant TBI (traumatic brain injury) is essential and attention must be paid to TBI's effects on executive functioning and care, which can significantly impact a child's future, Ullman said. 

"With sufficient injury, the central nervous system, and the brain, in particular, may not function as well as before," Fornari added. But it's still not clear whether the ADHD is there from the time of the head injury or whether it develops over time, Narad said.

It could be that the injured preschoolers had not yet been put into a situation that would highlight their ADHD, Narad said. Middle school requires much more attention and higher organizational skills from kids.

"We know that concussion recovery is very different than the more severe brain injury recovery," Narad said. "There are some kids who experience a concussion which has some attention problems. Those can resolve, and sometimes they might persist for a little longer. But the risk as not as great as with these more severe injuries."