The incomplete-hippocampal-inversion (IHI), also known as malrotation, is an
atypical anatomical pattern of the hippocampus, which has been reported in
healthy subjects in different studies. However, extensive characterization of
IHI in a large sample has not yet been performed. Furthermore, it is unclear
whether IHI are restricted to the medial-temporal lobe or are associated with
more extensive anatomical changes. Here, we studied the characteristics of IHI
in a community-based sample of 2008 subjects of the IMAGEN database and their
association with extra-hippocampal anatomical variations. The presence of IHI
was assessed on T1-weighted anatomical magnetic resonance imaging (MRI) using
visual criteria. We assessed the association of IHI with other anatomical
changes throughout the brain using automatic morphometry of cortical sulci. We
found that IHI were much more frequent in the left hippocampus (left: 17%,
right: 6%, χ2−test, p < 10−28). Compared to subjects without IHI, subjects
with IHI displayed morphological changes in several sulci located mainly in
the limbic lobe. Our results demonstrate that IHI are a common left-sided
phenomenon in normal subjects and that they are associated with morphological
changes outside the medial temporal lobe