Perivascular Space Morphology Is Affected By Career Exposure In Special Operations Forces Combat Soldiers

Abstract

Special Operations Forces (SOF) combat Soldiers are at high risk for repetitive blast and head impact exposure. These exposures may predispose SOF combat Soldiers to acute brain injuries and subsequent chronic manifestations including sleep disorders reported by 40% of US Service Members. Studying brain morphology such as perivascular spaces (PVS) may illustrate a strong intersection between brain glymphatic system function and sleep quality. Cerebral PVS are glymphatic system passageways normally serving to clear brain metabolic waste during sleep. Increasing MRI visible PVS number and volume are a possible pathogenesis for neurodegenerative disorders. PURPOSE: To determine the association between PVS morphological characteristics and career stage in SOF combat Soldiers. METHODS: Healthy asymptomatic SOF combat Soldiers (age=33.0±4.1yrs) cross-sectionally participated in this study at two career stages: baseline (n=141) and in-career (n=76). We collected whole brain 3D T2-weighted magnetic resonance imaging (MRI) on a Siemens 3T Biograph mMR or 3T MAGNETOM Prisma with equivalent settings (TR/TE = 3200/400ms, slice thickness = 1mm, FoV = 256mm x 256 mm). We segmented the PVS using validated multi-scale deep convolutional encoder-decoder neural networks. All images were skull stripped and registered to a custom brain atlas using Advanced Normalization Tools to identify only PVS clusters within cerebral white matter. We quantified PVS number and volume. The PVS outcome variables were non-normally distributed. As such, we employed nonparametric Mann Whitney U tests to compare the two career stage groups. RESULTS: Median (IQR) data were as follows: PVS number = 37.0 (44.0); PVS volume = 647mm3 (972mm3). In-career SOF combat Soldiers had greater PVS number (z = 2.56, P = 0.01) and PVS volume (z = 2.28, P = 0.02). CONCLUSIONS: In-career SOF combat Soldiers (typically older) show higher segmented PVS number and volume compared to baseline cohort. Also, our PVS findings may indicate impairments with clearing brain wastes suggesting sleep interventions may be warranted in SOF combat Soldier populations who experience continued exposures to combat and training. Measuring the PVS may be an important outcome in determining the efficacy of sleep studies in this population. Funded by US Special Operations Command.