Brain Structural Changes in Blast-Exposed Special Operations Forces Soldiers

Special Operations Forces (SOF) soldiers experience frequent low-level occupational blast exposure and mild traumatic brain injury (mTBI), but the cumulative effects of these exposures on long-term neurological health remain poorly understood. The purpose of this longitudinal cohort study was to investigate associations between occupational blast exposure and brain structural change in SOF soldiers and to determine whether mTBI sustained between assessments moderated these associations. Male SOF soldiers (n = 88) underwent T1- and T2-weighted magnetic resonance imaging at two timepoints. Volumetric segmentation was performed using FreeSurfer. Main outcomes were percent change in global brain tissue volumes, including cerebral cortex, cerebral white matter, lateral ventricles, subcortical gray matter, and cerebellar cortex. Exposure was quantified as months between Time 1 and Time 2, used as a proxy for cumulative occupational blast exposure during time in a high-tempo operational unit. The number of self-reported mTBIs sustained between timepoints was categorized as 0, 1-2, or 3 or more injuries. The Benjamini-Hochberg procedure was applied to control the false discovery rate. Greater occupational blast exposure predicted increased lateral ventricle percent change (F_1,86 = 9.86; B = 0.126%; R² = 0.103; p = 0.002; p-adjusted = 0.012) and decreased cerebellar cortex percent change (F_1,86 = 5.72; B = -0.074%; R² = 0.062; p = 0.019; p-adjusted = 0.047). Between-visit mTBI did not significantly moderate these associations. In this cohort of SOF soldiers, greater cumulative occupational blast exposure was associated with lateral ventricular expansion and cerebellar cortex volume loss. The rate of ventricular expansion observed in this study is atypical compared with expected change in healthy adults and may represent an early structural marker of blast-related brain vulnerability. Cerebellar cortex volume loss may reflect regional susceptibility to blast-related injury. Identifying brain structural changes associated with occupational blast exposure may help inform exposure-monitoring strategies and targeted interventions to preserve warfighter brain health and readiness.