Cavum Septum Pellucidum Enlargement in Special Operations Forces Members Is Associated with Lifetime Exposure to Large Explosives

Cavum septum pellucidum (CSP) is a common neuroimaging finding linked to repetitive head trauma, yet its relationship to blast exposure among the military population remains elusive. Here, we investigated whether lifetime exposure to different types of blast is associated with CSP morphology among Special Operations Forces (SOF) personnel. We retrospectively analyzed 323 SOF members from the Comprehensive Brain Health and Trauma Program at Home Base who completed high-resolution 3T MRI and the Blast Exposure Threshold Survey (BETS), which quantifies lifetime exposure to explosive weapons across five blast exposure count categories (BEC1-BEC5). CSP grade and length were assessed using validated criteria on coronal 3D T1-weighted Magnetization Prepared Rapid Gradient Echo scans. A CSP length-to-septum length ratio (CSP ratio) was calculated to adjust for anatomical variation. BEC1-BEC5 were log-transformed to correct skewness and are referred to as log-BEC1-5.Variance inflation factor analysis indicated low multicollinearity among predictors (log-BEC1-5 and age), and variable selection using Least Absolute Shrinkage and Selection Operator regression identified log-BEC5 (exposure to large explosives) as the only retained predictor. In fully adjusted models, only log-BEC5 remained significantly associated with CSP measures and was therefore the focus of subsequent analyses.Participants were stratified by BEC5 = 0 vs. BEC5 > 0, and associations with CSP measures were assessed using group comparisons, multivariable regression, and dose-response models.Among 323 participants (mean age 42.7 ± 8.8 years), 273 (84%) reported any BEC5 exposure. SOF members with BEC5 > 0 had significantly greater CSP presence (42.1% vs. 22.0%, <i>p</i> = 0.007) and longer CSP length (median 3 mm vs. 2 mm, <i>p</i> = 0.002). In age-adjusted models, BEC5 > 0 was associated with greater odds of CSP presence (OR = 2.58, 95% CI 1.26-5.25, <i>p</i> = 0.009) and a 1.45 mm increase in CSP length (<i>p</i> = 0.004). In continuous models, each one-unit increase in log-BEC5 was associated with a 0.31 mm increase in CSP length (<i>p</i> = 0.008) and a 0.0059 increase in CSP ratio (<i>p</i> = 0.008).These findings indicate a statistically significant association between cumulative exposure to heavy explosives and CSP enlargement, suggesting that CSP may serve as a potential imaging marker of blast-related neurotrauma.