Doctors have known for a long time that in some patients, damage to the brain lingerers long after an injury is inflicted by an explosion or a physical blow. Yet the causes of long-term problems from even mild concussions are often invisible to standard brain-scanning techniques.
Recently, scientists have used several unusual imaging methods to detect the long-term effects of brain injury in several experiments on humans or mice.
The most recent study, presented Dec. 2, involved a special magnetic resonance imaging method that was able to detect damage to nerve-signal-carrying white matter in the brains of veterans exposed to a blast.
Such injury is difficult to detect with standard imaging techniques.
P. Tyler Roskos, a neuropsychologist at St. Louis University School of Medicine, told the Radiological Society of North America's annual meeting in Chicago that the test showed damage to those nerve channels in 10 veterans of Iraq and Afghanistan enduring an average of more than four years after their traumatic brain injury was first diagnosed. About 20 percent of veterans returning from the field in those wars have some level of brain trauma from an explosion.
The imaging technique was actually able to measure changes in water movement along the signal channels, or axons, associated with damage from the injury. The researchers compared the effect to multiple tiny leaks in a garden hose.
By comparing brain images of the 10 injured veterans with those of 10 healthy volunteers, the researchers were able to measure how uniformly water is diffused through the brain and see where low levels indicate areas where axons are injured.
Roskos said such long-term impacts on the brain may account for continuing cognitive and behavioral changes in some veterans with a history of blast-related brain trauma, and may also help in determining whether a veteran is experiencing difficulty from a physical brain injury or psychological damage from post-traumatic stress, or perhaps both, and guide treatment accordingly.
Another study done in mice suggests that a single mild blast exposure can cause brain injuries that modify structures or molecules related to degenerative diseases like Alzheimer's.
Researchers from the VA Puget Sound Health Care System reported in September that mice exposed to just one blast had elevated levels of modified Tau protein that endured for at least a month.
This altered form of the protein is the building block for "tau tangles" that build up over time and damage brain cells. The work appeared in the Journal of Alzheimer's Disease.
Returning to human brains, a third study reported in March that there can be lasting structural damage to key brain regions for a year or more in some patients following a single concussion.
Radiologists at the New York University Langone School of Medicine did three-dimensional MRIs of 19 individuals with post-traumatic symptoms after a concussion and on 12 uninjured control subjects, repeating the imaging for most after a year. The results were published in the journal Radiology.
They measured the total volume of brain cells and nerve fibers throughout the brain and in specific regions, and found that a year after a concussion there was still measurable atrophy among the injured patients compared with the healthy ones. In particular, areas of the brain linked to mood disorders and more complex thinking appeared to have lingering volume loss.
The federal Centers for Disease Control and Prevention estimates that 1.7 million Americans sustain traumatic brain injuries each year, with 75 percent of them considered "mild" or a concussion. While many people recover from a concussion in a few weeks, earlier studies have shown 10 to 20 percent suffer from neurological or psychological symptoms more than a year after they are injured.
Dr. Yvonne Lui, an assistant professor of radiology who led the study, said the findings are the first to show this kind of damage continuing after a single concussion, rather than only in people who have sustained moderate to severe head trauma.
She stressed that such damage may not be present in everyone with a concussion, but helps to explain why some have long-term symptoms.