Pathology in the Brain After mTBI - A Multimodal MRI Study

More than 25,000 people in Denmark, are each year diagnosed with commotio cerebri as a result of head trauma (National Patient Registry, 1996), and foreign studies report that up to 5 to 15% of these have symptoms that persist beyond 3 months (5). Post commotio symptoms (PCS) are typically divided into physical, cognitive and emotional symptoms and include headache, fatigue, memory loss, stress, etc.. It is known from previous studies of traumatic brain injuries that the cost of the disabling process and the failure to intervene in the long term are very costly (11). In Denmark there are to date no systematic or consistent treatment for people with persistent symptoms 3 months after commotio cerebri, and a lack of general knowledge about the pathology and standardization with regard to diagnosis and prognosis are also missing.

Commotio cerebri, also known as mild traumatic brain injury (mTBI) is often defined as an exogenous traumatic stimulus that causes a physiological disruption of brain function (American Congress of Rehabilitation Medicine). This includes a biochemical cascade, edema, micro-haemorrhages, diffuse axonal injury (DAI) and changes in activity between internal networks in the brain (12, 13).

In severe trauma, conventional scanning methods such as Computer Tomography (CT) and Magnetic Resonance Imaging (MRI) can detect bone rupture, edema and micro-haemorrhages, but in mTBI, it is often difficult to detect edema or micro-hemorrhages, and the conventional methods is often not sensitive enough to show pathology especially beyond the acute period, although patients continue to have physical symptoms as well as cognitive and emotional problems (6, 12).

More MRI techniques, which are not routinely used in the clinic, has verified both DAI and changes in cortical network as compared to healthy controls (12). One of these is the method Diffusional tensor imaging (DTI) which can be used to detect the DAI in white matter (WM). DTI studies confirm DAI in several WM areas after mTBI (12). Other studies have shown that DAI detected by DTI in several places of WM correlates with cognitive problems after mTBI (1,2,6,13).

A more recent and less studied MRI method is Diffusional Kurtosis Imaging (DKI) which can display DAI in WM and prove to be more sensitive than the DTI for the detection of damage in gray matter (GM) (3, 4). A study in humans showed significant differences between individuals with mTBI and healthy controls, in the thalamus and several WM areas (3). This study also showed a correlation between DKI markers in the thalamus and the capsula interna with cognitive problems in multiple domains after mTBI. DKI is therefore suggested to be used in addition to DTI in relation to detect tissue damage in both WM and GM.