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Abnormal hippocampal morphology in dissociative identity disorder and post‐traumatic stress disorder correlates with childhood trauma and dissociative symptoms

Smaller hippocampal volume has been reported in individuals with post‐traumatic stress disorder (PTSD) and dissociative identity disorder (DID), but the regional specificity of hippocampal volume reductions and the association with severity of dissociative symptoms and/or childhood traumatization are still unclear. Brain structural magnetic resonance imaging scans were analyzed for 33 outpatients (17 with DID and 16 with PTSD only) and 28 healthy controls (HC), all matched for age, sex, and education. DID patients met criteria for PTSD (PTSD–DID). Hippocampal global and subfield volumes and shape measurements were extracted. We found that global hippocampal volume was significantly smaller in all 33 patients (left: 6.75%; right: 8.33%) compared with HC. PTSD–DID (left: 10.19%; right: 11.37%) and PTSD‐only with a history of childhood traumatization (left: 7.11%; right: 7.31%) had significantly smaller global hippocampal volume relative to HC. PTSD–DID had abnormal shape and significantly smaller volume in the CA2‐3, CA4‐DG and (pre)subiculum compared with HC. In the patient groups, smaller global and subfield hippocampal volumes significantly correlated with higher severity of childhood traumatization and dissociative symptoms. These findings support a childhood trauma‐related etiology for abnormal hippocampal morphology in both PTSD and DID and can further the understanding of neurobiological mechanisms involved in these disorders. Hum Brain Mapp 36:1692–1704, 2015. © 2014 Wiley Periodicals, Inc.