Using a advanced form of MRI, researchers found unique structural abnormalities in the brains of US troops with mild blast-related traumatic brain injuries that have not been seen with other types of scanning technology. In a study published this week in the New England Journal of Medicine, they emphasize, however, that their findings are tentative, the significance of the abnormalities is not yet fully understood, and more work needs to be done to establish whether the abnormalities represent significant brain damage.
The team includes researchers from the Washington University School of Medicine in St. Louis in the US and the Landstuhl Regional Medical Center in Landstuhl, Germany.
They examined US soldiers who had been wounded in the wars in Iraq and Afghanistan and evacuated to Landstuhl. Many such evacuees have a disproportionate number of injuries, including brain trauma, from blasts caused by improvised explosive devices (IEDs).
Estimates suggest as many as 320,000 soldiers have suffered traumatic brain injury in the wars in Iraq and Afghanistan, mostly classifed as mild traumatic brain injury, or concussion.
But, as senior study author Dr David L Brody, assistant professor of neurology at Washington University School of Medicine, told the press:
“We call these injuries ‘mild’, but in reality they sometimes can have serious consequences.”
For the study, Brody and colleagues took advanced MRI brain scans of 84 injured soldiers and found unique structural abnormalities in 18 of 63 diagnosed with traumatic brain injury, but not in 21 who had suffered other types of injury.
The abnormalities they found were in the white matter of the brain: specifically damage to axons, the nerve fibres that enable brain cells to communicate with each other.
The damaged fibers were found in two places: the orbitofrontal cortex, located at the front of the brain behind the eyes, and the cerebellum, thats sits at the back, underpart of the brain. The first of these helps regulate emotion and reward-based behavior, and the second is involved in controlling movement, coordination, and also organization and planning.
The MRI method they used is called DTI, short for “diffusion tensor imaging”, a method that tracks the movement of water in tissue. Although DTI-detected change in the pattern of water movement is often injury-related, the researchers said it was not possible to tell from their results how significant the abnormalities may be.
These particular abnormalities have not been found in DTI scans of civilians with mild traumatic brain injury, although the scans in this study did show abnormalities in parts of the brain known to be affected in civilian trauma.
Lead author Dr Christine L Mac Donald, research instructor in neurology at Washington University, said:
“There is still a lot more work to be done before we fully understand whether these abnormalities truly represent significant damage to the brain white matter.”
The nub of the problem will be assessing how this type of damage affects a range of functions important to the patient’s quality of life, such as attention, memory, sleep, balance, coordination, and regulation of emotion. There are also questions about how it might influence the link between mild traumatic brain injury and post-traumatic stress disorder (PTSD).
There is an urgent need in research to improve the diagnosis of traumatic brain injury and differentiate it from PTSD.
“Our ongoing studies will hopefully start to answer some of these questions,” said Mac Donald.
Mild traumatic brain injury is a controversial topic because it is not possible always to establish if the symptoms are caused by changes in brain chemistry, structural damage, psychological factors, or a combination of some or all of these.
The results of this study suggest there may be fundamental differences between the brain injuries caused by bomb-blasts and the types of brain injury normally sustained by civilians, such as in road traffic accidents, sports, falls and blows to the head.
However, because all the soldiers who took part in this study also had other injuries sustained during the bomb-blast, such as from hitting their head in a vehicle crash, falls, or being hit by a blunt object, it was not possible to separate out the direct effects from the blasts.
This is relevant because, as Dr Allan Ropper, a neurologist at Brigham and Women’s Hospital, Boston, points out in an accompanying editorial, there has been skepticism about whether a bomb that goes off at a distance and causes no visible wound can penetrate the skull and damage the brain.
Part of the problem is the complexity of the physics and thereby determining what exactly causes injury. First, there is an initial shock wave, then a supersonic wind, and a reverse underpressure, the scale of these depending on the inverse square of the distance. Injury occurs at various points in the unfolding timescale of these events, not necessarily at a single point, as Ropper explains:
“Tissues are damaged when the shock energy is dissipated at the interface between air and liquid that presents a change in acoustic impedance. The blast wind is the source of separate injury, throwing people against fixed objects and dispersing projectiles that penetrate the body.”
The researchers said they could detect the white matter abnormalities up to a year after injury, although the DTI scans showed they changed with time.
Ropper suggests there are two key findings in the research. The first is the clear difference in results between DTI scans as opposed to conventional MRI: many regions of axonal disruption show up with DTI that MRI can’t spot. The second is when the researchers did further DTI scans at follow-up 6 and 12 months later, they could see the abnormalities had evolved in a way that suggests the injuries did in fact occur at the time of the blast and were not the result of head injuries from another event.
“We now have tentative validation in mild traumatic brain injury of the disruption of cerebral axons by blasts from improvised explosive devices. Even if this information is exploratory, with further information on the relationship among blasts, axonal damage, and PTSD anticipated in the future, soldiers injured in this way and their resultant disability deserve the utmost attention,” writes Ropper.
In the meantime, Brody points out that the diagnosis of mild traumatic brain injury is still based on the history of an injury to the head that results in loss of consciousness, loss of memory, confusion, or other signs of brain disruption.
“A negative MRI scan, even with these advanced methods, does not rule out mild traumatic brain injury,” he emphasizes, adding that:
“These MRI-based methods show great promise, but are not yet ready to be used in routine clinical practice.”
However, he and his colleagues are optimistic that the study will increase understanding of brain injury not only in soldiers but also in civilians, including children.
“Detection of Blast -Related Traumatic Brain Injury in U.S. Military Personnel.”, Christine L. Mac Donald et al., N Engl J Med 2011; 364:2091-2100, published online 2 June 2011.
Additional source: Washington University School of Medicine.
Written by: Catharine Paddock, PhD