Researchers say thousands of troops who suffered traumatic brain injuries in Iraq and Afghanistan are at risk of long-term health problems, including depression and Alzheimer's-like dementia.
But they say it's impossible to predict how high those risks are.
The prestigious Institute of Medicine says about 22 percent of wounded troops have a brain injury, and it urges precise steps for studying how these patients fare years later so chances to help aren't missed.
In traumatic brain injury the damage is caused by an explosion's pressure wave and is hidden inside the skull. It can range from a mild concussion to severe injury. And because symptoms may not be immediately apparent, troops may not seek care.
The Veterans Affairs Department, which requested the report, and the Pentagon already are taking some of the recommended steps.