Volume and shape analysis of the Hippocampus and amygdala in veterans with traumatic brain injury and posttraumatic stress disorder

There is a need to improve the understanding of the neurobiological underpinnings of traumatic brain injury (TBI). Individuals with TBI experience comorbidities such as posttraumatic stress disorder (PTSD) with considerable symptom overlap including depression and hyperarousal, confounding the ability to identify specific TBI-related brain changes. The aims of the current study were to investigate hippocampal and amygdalar volumes in Veterans with TBI with (TBI + PTSD, n = 32) and without (TBI - PTSD, n = 25) PTSD. Shape analysis was employed to reveal any relationship between the hippocampus and depressive symptoms in TBI subgroups. 32 TBI + PTSD, 25 TBI - PTSD, and 25 age-matched healthy male Veterans underwent an MRI scan on a 3 Tesla scanner and a clinical evaluation. The TBI + PTSD and the TBI + hyperarousal (met criteria for the hyperarousal symptom cluster, regardless of PTSD diagnosis) subgroup had trend-level larger left amygdalar volume than the TBI - PTSD subgroup and the TBI - hyperarousal subgroup, respectively. However, there was no significant difference between the TBI group as a whole and healthy controls (HC). There was a significant negative correlation between the Hamilton Rating Scale for Depression score (HAM-D) and left hippocampal volume and a positive correlation between the HAM-D score and left amygdalar volume in the TBI group. Left hippocampal volume was correlated with the HAM-D score only in the TBI + PTSD and not in TBI - PTSD subgroup. Shape analyses revealed a significant correlation between the HAM-D score and the CA1 and subiculum regions of the left hippocampus. Our results suggest that the amygdala may be a neuroanatomical correlate in mediating PTSD-like symptoms in Veterans with TBI. The results of shape analysis suggest that alterations in the CA1 and subiculum subregions of hippocampus may have a role in depression and PTSD.