Hippocampal Alterations in Autism Spectrum Disorder: A Scoping Review of Magnetic Resonance Imaging

Autism Spectrum Disorder (ASD) is a neurodevelopmental condition defined by impairments in social communication and interaction alongside restricted and repetitive patterns of behavior or interests. Alterations in the hippocampus are likely associated with cognitive and behavioral manifestations of ASD. This study aims to map the methods used in Magnetic Resonance Imaging (MRI) of the hippocampus in ASD and to investigate its reported alterations.

We performed a literature search using Medical Subject Headings (MeSH) and keywords across PubMed, Embase, BVS, Web of Science, Scopus, Cochrane Library, and PsycINFO. Original case-control, cross-sectional, and longitudinal studies evaluating patients with ASD using MRI were eligible for inclusion. Data was manually extracted and charted in four tables.

A total of 104 studies were included, encompassing neuroimaging modalities such as structural morphometry, diffusion imaging, magnetic resonance spectroscopy, functional magnetic resonance imaging, and perfusion imaging. Reported findings across studies included atypical hippocampal overgrowth during early development, reduced N-acetylaspartate levels in children, chronic hypoperfusion extending into early adulthood, hyperrecruitment of specific hippocampal regions that improperly connect with cortical areas, reduced microstructural integrity in adulthood, and a notable decline in hippocampal volume as individuals age.

The current evidence suggests that the hippocampus may undergo multimodal alterations in ASD, spanning morphometric, microstructural, metabolic, functional, and perfusion domains, and that these alterations may be age-dependent. Longitudinal research is required to delineate age-specific thresholds for these changes and elucidate their associations with neurodevelopmental outcomes in ASD.