Structural Neuroimaging of Hippocampus and Amygdala Subregions in Posttraumatic Stress Disorder: A Scoping Review

Abstract

Numerous studies have explored the relationship between posttraumatic stress disorder (PTSD) and the hippocampus and the amygdala because both regions are implicated in the disorder's pathogenesis and pathophysiology. Nevertheless, those key limbic regions consist of functionally and cytoarchitecturally distinct substructures that may play different roles in the etiology of PTSD. Spurred by the availability of automatic segmentation software, structural neuroimaging studies of human hippocampal and amygdala subregions have proliferated in recent years. Here, we present a preregistered scoping review of the existing structural neuroimaging studies of the hippocampus and amygdala subregions in adults diagnosed with PTSD. A total of 3513 studies assessing subregion volumes were identified, 1689 of which were screened, and 21 studies were eligible for this review (total N = 2876 individuals). Most studies examined hippocampal subregions and reported decreased CA1, CA3, dentate gyrus, and subiculum volumes in PTSD. Fewer studies investigated amygdala subregions and reported altered lateral, basal, and central nuclei volumes in PTSD. This review further highlights the conceptual and methodological limitations of the current literature and identifies future directions to increase understanding of the distinct roles of hippocampal and amygdalar subregions in posttraumatic psychopathology.

Figure 1

The hippocampus and amygdala subregions were grouped across all reviewed studies (n = 21) based on the well-established literature of their anatomy and function and on their absolute size because larger subregions showed greater test-retest reliability across different magnetic resonance imaging sites and vendors. These results were generated with FreeSurfer 7.1.0 and are overlaid on an anatomical scan of a single subject. Amygdala nuclei (A) and hippocampal subfields (B) are displayed in 3 dimensions on coronal and sagittal planes, with a black line separating the two. The amygdala subregions are presented bilaterally, whereas the hippocampal subregions are presented unilaterally. CA, cornu ammonis.

Figure 2

Flow of information through different phases of the review according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. PTSD, posttraumatic stress disorder; TBI, traumatic brain injury.