Solar, K.G., Treit, S. and Beaulieu, C. (2022), High-resolution diffusion tensor imaging identifies hippocampal volume loss without diffusion changes in individuals with prenatal alcohol exposure. Alcohol Clin Exp Res. Accepted Author Manuscript. https://doi.org/10.1111/acer.14857
Magnetic resonance imaging (MRI) studies of prenatal alcohol exposure (PAE) commonly report reduced hippocampal volumes, which animal models suggest may result from microstructural changes including cell loss and altered myelination. Diffusion tensor imaging (DTI) is sensitive to microstructural changes but has not yet been used to study the hippocampus in PAE.
36 healthy controls (19 females; 8-24 years) and 19 participants with PAE (8 females; 8-23 years) underwent high-resolution (1 mm isotropic) DTI, anatomical T1-weighted imaging, and cognitive testing. Whole-hippocampus, head, body and tail subregions were manually segmented to yield DTI metrics (mean, axial, radial diffusivities – MD, AD, RD; fractional anisotropy – FA), volumes, as well as qualitative assessments of hippocampal morphology and digitations. Automated segmentation of T1-weighted images was used to corroborate manual whole-hippocampus volumes.
Gross morphology and digitation counts were similar in both groups. Whole-hippocampus volumes were 18% smaller in the PAE than control group on manually-traced diffusion images, but automated T1-weighted image segmentations were not significantly different. Subregion segmentation on DTI revealed reduced volumes of the body and tail, but not head. There were no significant differences in diffusion metrics between groups for any hippocampal region. Correlations between age and volume were not significant in either group, while negative correlations between age and whole-hippocampus MD/AD/RD, and head/body (but not tail) MD/AD/RD were significant in both groups. There were no significant effects of sex, group-by-age or group-by-sex for any hippocampal metric. In controls, 7 positive linear correlations were found between hippocampal volume and cognition; 5 of these were left-lateralized and included episodic and working memory, and 2 were right-lateralized and included working memory and processing speed. In PAE, left tail MD positively correlated with executive functioning, and right head MD negatively correlated with episodic memory.
Reductions of hippocampal volumes and altered relationships with memory suggest disrupted hippocampus development in PAE.