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. 2015 Dec 22;9:160.
doi: 10.3389/fnana.2015.00160. eCollection 2015.

Incomplete Hippocampal Inversion: A Comprehensive MRI Study of Over 2000 Subjects

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Free PMC article

Incomplete Hippocampal Inversion: A Comprehensive MRI Study of Over 2000 Subjects

Claire Cury et al. Front Neuroanat. .
Free PMC article

Abstract

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%, χ(2)-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.

Keywords: IMAGEN database; Large database; MRI; anatomical variability; brain development; cortical sulci; human hippocampus; malrotation.

Figures

Figure 1
Figure 1
Illustration of the 5 criteria used for the evaluation of Incomplete Hippocampal Inversions. C1: Roundness and verticality. The horizontal arrow (C1a) goes from the medial part of the Dentate Gyrus (DG) to the lateral part of the hippocampus. The vertical arrow (C1b) goes from the bottom to the top part of the Cornus Ammonis (CA) C2: Verticality and depth of the collateral sulcus. The vertical line indicates the lateral border of the hippocampus which is used to determine if the sulcus is deep or not. CS indicates the collateral sulcus and OTS the occipito temporal sulcus. C3: Medial positioning. The C3a segment indicates the part of the subiculum (Sb) not covered by the DG. The C3b segment indicates the part of CA covered by the DG. C5: Orientation of the sulci of the fusiform gyrus. The dotted lines indicate the top of the sulci CS and OTS. The upper part of the subiculum is the red area.
Figure 2
Figure 2
For each IHI criterion, examples corresponding to 3 different grades (0, 1, 2) are displayed.
Figure 3
Figure 3
Sulci segmented via the Morphologist toolbox of the Brainvisa software.
Figure 4
Figure 4
Histograms of the sum of grades of individual criteria categorized by the global criterion C0, for left (A) and right (B) hippocampi.
Figure 5
Figure 5
Sulci of the left hemisphere (top) significantly different for left hippocampi with or without IHI. Sulci of the right hemisphere (bottom) significantly different between right hippocampi with or without IHI. The color map indicates the value of the corrected p-value. p > 0.05 are in blue.

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