Size versus shape differences:: Contrasting voxel-based and volumetric analyses of the anterior cingulate cortex in individuals with acute posttraumatic stress disorder

Background: Two studies found morphological differences in the anterior cingulate cortex (ACC) of individuals with chronic posttraumatic stress disorder (PTSD). We sought to replicate and extend these findings in a sample of individuals with acute PTSD. Methods: The ACCs of individuals with acute PTSD (n = 14) and matched healthy control subjects (n = 14) were compared using voxel-based morphometry (VBM), semi-automated volumetric analyses, and probabilistic maps. Posttraumatic stress disorder diagnosis was ascertained by a psychologist using a structured interview. Results: Voxel-based morphometry analyses revealed significantly less gray-matter density in the right pregenual ACC and in the left insula of the PTSD group. However, volumetric analyses of the ACC revealed no significant differences between groups. Probabilistic maps of the labels of the pregenual ACC indicated that the difference between groups in gray matter density was due to shape differences. Conclusions: Although there are no volumetric differences in the ACC of acute PTSD individuals compared with normal control subjects, significant shape differences exist, which might indicate volumetric differences in the surrounding structures.