Volumetric analysis of medial temporal lobe subregions in developmental amnesia using high-resolution magnetic resonance imaging.

There is great interest in the cognitive consequences of hippocampal volume loss in developmental amnesia (DA). In many DA cases, volume loss occurs before the hippocampus is fully developed, and yet little is known about the locus, extent, and distribution of damage in these cases. We used high-resolution MRI to manually segment the medial temporal lobe (MTL) subregions in H.C., an adult with DA, and a group of sex-, age- and education-matched control participants (n = 10). The hippocampus was defined and divided into anterior (head) and posterior (body and tail) segments. Within the body of the hippocampus, the subregions (CA1 , DG/CA2/3 , and subiculum) were defined. Finally, the entorhinal (ERC), perirhinal (PRC), and parahippocampal (PHC) cortices were segmented. Anterior hippocampus was reduced bilaterally and posterior hippocampus was significantly reduced on the right. In the body of the hippocampus, all three subregions were reduced in the left hemisphere, whereas CA1 and subiculum were reduced in the right hemisphere. No group differences were observed in the PRC and ERC, whereas left PHC volume was marginally increased in H.C. compared to controls. These results can be used to inform patterns of spared and impaired cognitive abilities in DA and perhaps in amnesia more generally.