Traumatic Brain Injury, Pt. 5

Accuracy of Imaging Tools

Fluid attenuated inversion recovery (FLAIR) is a pulse sequence (signals) used in MRIs to detect brain abnormalities. Researchers studying FLAIR signals have recently concluded that abnormal FLAIR lesions characterized by acute hyperintensity are strongly predictive of global brain atrophy following TBI. However, researchers caution that FLAIR technology may not be the most sensitive MR to detect DAI. Newer, more sophisticated forms of imaging, such as 3D gradient echo MRI imaging or susceptibility-weighted imaging (SWI)—is far more sensitive in detecting microbleeds than earlier forms of MRIs. Diffusion weighted imaging, also known as DWI, has proven to be highly effective for detecting of cytotoxic cerebral edema –a type of brain edema in which the blood-brain barrier remains intact—in cases of acute stroke. However, it has shown no more sensitivity in identifying DAI lesions that FLAIR.

Other programs, including SIENA (Structural Image Evaluation, using Normalization, of Atrophy) and SIENAX are now being used to measure temporal brain change by inputting two MRI images, taken at different points in time, and then comparing the two images for signs of atrophy. SIENA has also been modified to a single-time point method which measures atrophy state rather than rate.

It is not unusual for many scans to be taken within the first week or within the first days following TBI. Ideally, scans obtained within the first 24 hours of a suspected TBI should be studied for differences with images taken during the subacute (>3 months) or chronic stage (>6 months) as it is possible that FLAIR lesions can be more easily spotted over time.

White Matter versus Gray Matter

Post-concussion syndrome is a complex disorder in which various symptoms — such as headaches and dizziness — last for weeks, months and even years after the initial injury. The syndrome has been poorly understood because it does not seem to be correlated with the severity of the initial injury. 20-30% of people who sustain MTBI will develop some degree of post-concussion syndrome. Until recently, clinicians did not understand why someone with a relatively mild injury could develop severe and prolonged impairment. Now brain researchers believe they may have found the answer with new insight into the “white matter” of the brain.

Gray matter is located in the outermost portion of the brain and contains neurons, the specialized cells responsible for storing and processing information: i.e., learning and memory. For years, scientists believed that brain injuries disproportionately affected the brain’s gray matter. In fact, white matter was considered pretty much of a passive tissue, having little to do with learning and brain functions. More recently, white matter has been found to “matter” very much, serving to regulate signaling, distributing and relaying communication messages to different parts of the brain.

In 2014, researchers working at the University of Southern California discovered that white matter contains the scaffolding network that defines the information architecture comprising and supporting brain function. By mapping the brain’s white matter, these researchers also discovered that the most important areas of white matter and gray matter do not always overlap. Instead, white matter is sometimes responsible for signaling messages to remote areas of the brain. When white matter pathways sustained damage, brain areas served by that pathway either withered or had their functions taken over by other parts of the brain. This finding may help explain why someone with MTBI can suffer what appear to be disproportionately devastating effects (http://journal.frontiersin.org/Journal/10.3389/fnhum.2014.00051/abstract).

Who is at Greatest Risk and Precautions

Males are at higher risk of experiencing TBI than women. Youngest children and older adults are at highest risk for sustaining fall-related TBIs. Adolescents and young adults (15-24 years old) have the highest rates of motor vehicle-related TBIs. Older adults, ages 65 years and older, have the highest rate of hospitalizations resulting from TBI and are most likely to die from either TBI or TBI complications.