Five-Year Serial Brain MRI Analysis of Military Members Exposed to Chronic Sub-Concussive Overpressures

Abstract

Background: The Canadian Special Operations Forces Command conducts explosives operations and training which exposes members to explosive charges at close proximity. This 5-year longitudinal trial was conducted in follow-up to our initial trial which examined military breachers with MRI and EEG pre and post blast exposure.

Purpose: To examine brain MRI findings in military personnel exposed to multiple repeated blast exposures.

Study type: Five-year longitudinal prospective trial.

Population: Ninety-two males aged 23-42 with an average of 9.4 years of blast exposure.

Field strength/sequence: 3 T brain MRI/T1-weighted 3D with reconstruction in three planes, T2-weighted, T2-weighted fluid attenuated inversion recovery (FLAIR) 3D with reconstruction in three planes, T2-weighted gradient spin echo (GRE), saturation weighted images, DWI and ADC maps, diffusion tensor imaging.

Assessment: All MRI scans were interpreted by the two neuroradiologists and one neuroradiology Fellow in a blinded fashion using a customized neuroradiology reporting form.

Statistical tests: Matching parametric statistics represented the number of participants whose brain parameters improved or deteriorated over time. Odds ratio (OR) and 95% confidence intervals (CI) were computed using log regression modeling to determine volume loss, white matter lesions, hemosiderosis, gliosis, cystic changes and enlarged Virchow Robin (VR) spaces. A Kappa (κ) statistic with a 95% CI was calculated to determine rater variability between readers.

Results: A significant deterioration was observed in volume loss (OR = 1.083, 95% CI 0.678-1.731, permutation test), white matter changes (OR: 0.754, 95% CI 0.442-1.284, permutation test), and enlargement of VR spaces (OR: 0.775, 95% CI 0.513-1.171). Interrater reliability was low: κ = 0.283, 0.156, and 0.557 for volume loss, white matter changes, and enlargement of VR spaces, respectively.

Data conclusion: There were significant changes in brain volume, white matter lesions, and enlargement of VR spaces.

Evidence level: 2 TECHNICAL EFFICACY: Stage 2.

Keywords: MRI; brain volume loss; cavernoma; chronic traumatic encephalopathy; developmental venous anomaly (DVA).

FIGURE 1

Example of enlarged VR spaces. T2 FLAIR image showing enlarged VR spaces mainly in the posterior quadrants.

FIGURE 2

Example of hemosiderosis. SWI image showing superficial hemosiderin deposit.

FIGURE 3

Example of white matter changes. T2 FLAIR image showing multifocal white matter changes.