White matter degeneration in diffuse axonal injury and mild traumatic brain injury observed with automatic tractography

Automated three-dimensional major white matter bundle segmentation using diffusion magnetic resonance imaging

White matter bundle segmentation using diffusion magnetic resonance imaging fiber tractography enables detailed evaluation of individual white matter tracts three-dimensionally, and plays a crucial role in studying human brain anatomy, function, development, and diseases. Manual extraction of streamlines utilizing a combination of the inclusion and exclusion of regions of interest can be considered the current gold standard for extracting white matter bundles from whole-brain tractograms. However, this is a time-consuming and operator-dependent process with limited reproducibility. Several automated approaches using different strategies to reconstruct the white matter tracts have been proposed to address the issues of time, labor, and reproducibility. In this review, we discuss few of the most well-validated approaches that automate white matter bundle segmentation with an end-to-end pipeline, including TRActs Constrained by UnderLying Anatomy (TRACULA), Automated Fiber Quantification, and TractSeg.

Concussion leads to widespread axonal sodium channel loss and disruption of the node of Ranvier

Despite being a major health concern, little is known about the pathophysiological changes that underly concussion. Nonetheless, emerging evidence suggests that selective damage to white matter axons, or diffuse axonal injury (DAI), disrupts brain network connectivity and function. While voltage-gated sodium channels (NaChs) and their anchoring proteins at the nodes of Ranvier (NOR) on axons are key elements of the brain's network signaling machinery, changes in their integrity have not been studied in context with DAI. Here, we utilized a clinically relevant swine model of concussion that induces evolving axonal pathology, demonstrated by accumulation of amyloid precursor protein (APP) across the white matter. Over a two-week follow-up post-concussion with this model, we found widespread loss of NaCh isoform 1.6 (Nav1.6), progressive increases in NOR length, the appearance of void and heminodes and loss of βIV-spectrin, ankyrin G, and neurofascin 186 or their collective diffusion into the paranode. Notably, these changes were in close proximity, yet distinct from APP-immunoreactive swollen axonal profiles, potentially representing a unique, newfound phenotype of axonal pathology in DAI. Since concussion in humans is non-fatal, the clinical relevance of these findings was determined through examination of post-mortem brain tissue from humans with higher levels of acute traumatic brain injury. Here, a similar loss of Nav1.6 and changes in NOR structures in brain white matter were observed as found in the swine model of concussion. Collectively, this widespread and progressive disruption of NaChs and NOR appears to be a form of sodium channelopathy, which may represent an important substrate underlying brain network dysfunction after concussion.

The ratio of serum neuron-specific enolase level to admission glasgow coma scale score is associated with diffuse axonal injury in patients with moderate to severe traumatic brain injury

Background

Moderate to severe traumatic brain injury (TBI) is frequently accompanied by diffuse axonal injury (DAI). Considering the low sensitivity of computed tomography (CT) examination for microbleeds and axonal damage, identification of DAI is difficult using conventional diagnostic methods in the acute phase. Neuron-specific enolase (NSE) has been demonstrated to be increased in serum following various types of TBI and is already clinically/commercially available. We conjecture that serum NSE level to admission GCS score ratio (NGR) may be a useful indicator for the early diagnosis of DAI.

Methods

This study included 115 patients with moderate-to-severe TBI who underwent NSE measurements within 6 h after injury and brain magnetic resonance imaging (MRI) within 30 days. The positive and negative DAI groups were divided according to MRI findings.

Results

Among the 115 patients, 49 (42.6%) were classified into the DAI group and 66 (57.4%) patients into the non-DAI group by clinical MRI. The NGR of patients without DAI was found to be significantly lower than those of patients with DAI (p < 0.0001). NGR presented the largest Pearson r value (r = 0.755, 95% CI 0.664–0.824, p < 0.0001) and high diagnostic accuracy for DAI [area under the curve (AUC) = 0.9493; sensitivity, 90.91%; and specificity, 85.71%]. Patients with TBI presenting with higher NGR were more likely to suffer an unfavorable neurological outcome [6-month extended Glasgow Outcome Scale (GOSE) 1–4].

Conclusions

The NGR on admission could serve as an independent predictor of DAI with moderate-to-severe TBI.