Research Letter: Blast Exposure and Brain Volume.

OBJECTIVE To determine whether blast exposure is associated with brain volume beyond posttraumatic stress disorder (PTSD) diagnosis and history of traumatic brain injury (TBI). SETTING Veterans Affairs Medical Center. PARTICIPANTS One hundred sixty-three Iraq and Afghanistan combat veterans, 86.5% male, and 68.10% with a history of blast exposure. Individuals with a history of moderate to severe TBI were excluded. MAIN MEASURES Clinician-Administered PTSD Scale (CAPS-5), Mid-Atlantic MIRECC Assessment of TBI (MMA-TBI), Salisbury Blast Interview (SBI), and magnetic resonance imaging. Maximum blast pressure experienced from a blast event represented blast severity. METHODS Hierarchical regression analysis evaluated effects of maximum pressure experienced from a blast event on bilateral volume of hippocampus, anterior cingulate cortex, amygdala, orbitofrontal cortex, precuneus, and insula. All analyses adjusted for effects of current and lifetime PTSD diagnosis, and a history of deployment mild TBI. RESULTS Maximum blast pressure experienced was significantly associated with lower bilateral hippocampal volume (left: ΔR2 = 0.032, P < .001; right: ΔR2 = 0.030, P < .001) beyond PTSD diagnosis and deployment mild TBI history. Other characteristics of blast exposure (time since most recent exposure, distance from closest blast, and frequency of blast events) were not associated with evaluated volumes. CONCLUSION Exposure to a blast is independently associated with hippocampal volume beyond PTSD and mild TBI; however, these effects are small. These results also demonstrate that blast exposure in and of itself may be less consequential than severity of the exposure as measured by the pressure gradient.