Important New Guidelines on Neuroimaging in Mild Traumatic Brain Injury
In July, 2013 the Defense Centers of Excellence, serving the United States Department of Defense, issued important new guidelines for neuroimaging following “mild” traumatic brain injury. The guidelines begin with the well-accepted understanding that neuroimaging is not typically included in the diagnosis of mild traumatic brain injury(“mTBI”) because only 10-15% of people who sustain trauma resulting in mTBI will have an acute brain lesion on CT (computed tomography) scans. “The lack of positive imaging findings,” the guidelines emphasize, “does not invalidate a diagnosis of mTBI.”
What is significant about the guidelines is that they recommend imaging in mTBI cases where the victim has “new, persistent or worsening symptoms” 90 days or more following the injury (described as the “chronic stage.”)
“The goal of imaging in the chronic stage of mTBI,” the guidelines say, “is to further evaluate the individual’s injury, enhance understanding of persistent symptoms, provide education and identify the need for specialist referral.”
The modality of choice for this imaging is MRI (magnetic resonance imaging.) Appendix A to the guidelines provides specific recommended protocols for MRI imaging, including 5 recommended “sequences” and two optional sequences. These MRI sequences, the guidelines explain, “may be 50% more sensitive than CT alone in detecting chronic lesions in white matter.” In other words, even these MRI studies will not show many lesions. The guidelines provide that if no structural abnormalities are identified in MRI or CT and symptoms persist, nuclear medicine scans, PET (positron emission tomography) or SPECT (single proton emission computed tomography) should be considered.
There has been controversy in the past around whether the various MRI sequences identified in the guidelines can be interpreted as showing particular mTBI pathologies. Table 2 in the guidelines supports the usefulness of these studies, outlining in detail the “Relationship Between Neuroimaging Techniques and Common mTBI Pathophysiology.” It explicitly acknowledges that “there is increasing evidence that specific MRI imaging techniques correspond, at least in a general way, with specific posttraumatic histopathology.” Examples given are that “diffusion tensor imaging (DTI) abnormalities are thought to correspond to axonal injury and susceptibility weighted imaging (SWI) abnormalities to microhemorrhages.”
The fact that a US Government agency is recognizing the benefit and usefulness of these imaging techniques is of great significance. It could change future clinical practices and support the use of these imaging findings in future litigation.