Evaluation of hippocampal infolding using magnetic resonance imaging.

To investigate developmental morphological variation of the hippocampal formation, we evaluated the degree of hippocampal infolding in cross-sectional oblique coronal images of the cerebral peduncle and the superior cerebellar peduncle. We defined the hippocampal infolding angle as the angle between the vertical midline and the straight line connecting the medial superior margin of the subiculum with the lateral margin of the cornu ammonis. The angle increased slightly with age, and was larger in the superior cerebellar peduncle than in the cerebral peduncle and larger in the right superior cerebellar peduncle than in the left superior cerebellar peduncle. This suggests that this angle and its variation with age and location merit our attention in morphological evaluation of the hippocampal formation.