WASHINGTON (AP) - As many as 20 percent of U.S. troops are coming home from war with signs they may have had a concussion, some of whom do not know they have symptoms that could be treated, Army officials said Thursday.

Concussion is a common term for mild traumatic brain injury. While the Army is doing a good job detecting more severe brain injuries, it is "challenged to understand, diagnose and treat military personnel who suffer with mild TBI," said Brig. Gen. Donald Bradshaw, chairman of a task force on traumatic brain injury created by the Army surgeon general.

The task force, which completed its work in May, released its findings on Thursday.

It estimated that from 10 percent to 20 percent of soldiers and Marines leaving Iraq and Afghanistan are affected by mild traumatic brain injury. The most common causes are a blast, motor vehicle accident, fall, and gunshot wound to the head or neck, the task force said.

The symptoms can include headaches, dizziness, nausea, light sensitivity, sleep problems, memory problems, confusion and irritability.