CHICAGO A blow to the head that knocks a person unconscious can result in widespread loss of brain tissue, Canadian researchers said on Monday, explaining why some people who suffer head injuries are never quite the same.
The more severe the injury, the more brain tissue is lost, they said.
"There is more damage and it is more widespread than we had expected," said Dr. Brian Levine of the Rotman Research Institute and the University of Toronto, whose study appears in the journal Neurology.
Levine studied brain scans taken from 69 traumatic brain injury patients whose head injuries ranged from mild to moderate or severe. The researchers used high-resolution magnetic resonance imaging or MRI to study changes in brain volume a year after the injury.
They ran a computer analysis of these images and found that even patients with mild brain injuries with no apparent scarring had less brain volume.
"When you have a blow to the head, it causes a neurochemical reaction in the brain cells that lead to cell death," Levine said in a telephone interview. "The more cells that die, the less tissue you have."
All the patients in the study had injuries severe enough that they needed to be hospitalized. "The amount of tissue loss seems to be related to the severity of the injury -- how long was the person was knocked out," Levine said.
He said the study helps to explain why some people with brain injuries often struggle with memory problems, mood changes, confusion and reduced information processing speed.
"What this study does is it gives us a window into the underlying brain structure changes that might relate to that disability," he said.
Levine said the brain volume lost involved both frontal and posterior brain regions, and the damage was greatest to white matter, tissue that makes up the brain's communication network.
"What you have basically is a loss of brain connectivity. That is essential for the efficient processing in the brain," he said. "When you have a subtle loss of that, even if it is 5 to 10 percent, it will have a large effect on behavior."
Levine said the study does not mean that people who have had mild head injuries will have a disability, but it might help to explain why some people never quite recover from their head injury.
"You hear this all the time from people, that they're not the same. A lot of times doctors don't know why," Levine said.
According the U.S. Centers for Disease Control and Prevention, at least, 1.4 million people in the United States suffer a traumatic brain injury each year.
At least 5.3 million Americans, or about 2 percent of the U.S. population, need help to perform activities of daily living as a result of their brain injuries.
(Editing by Maggie Fox and Eric Walsh)