AbstractBackgroundWe utilized 3‐dimensional, surface‐based, morphometric analysis to investigate hippocampus shape between 2 groups: (1) idiopathic normal‐pressure hydrocephalus (INPH) patients who had a positive response to the cerebrospinal fluid tap test and (2) healthy controls. The aims were (1) to evaluate INPH‐related structural abnormalities of the hippocampi and (2) to investigate relationships between hippocampal shape changes and gait disturbance in INPH patients.MethodForty‐eight INPH patients and 25 healthy controls were imaged with MRI, including 3‐dimensional volumetric images, for vertex‐based 3‐dimensional hippocampal shape analysis.ResultVertex‐wise shape analysis revealed significant bilateral deformation in patients with INPH compared with healthy controls after FDR correction. Both the left and right hippocampi were more elongated and narrowed in INPH patients than in the healthy controls. In both hemispheres, INPH patients demonstrated an upward bending of the middle and posterior hippocampus reflecting a bilateral vertical displacement from body to tail. Significant correlations were found between local shape deformity and the timed up and go and 10 meter walking tests (to a greater degree on the right than on the left). Bilateral inward deformations at the superomedial hippocampal tail and inferior hippocampal body were consistently associated with inferior performance across tests. Inward deformations at the right medial and lateral hippocampal head and right superior hippocampal body were also consistently associated with worse performance across tests.ConclusionThese results suggest that patients with INPH have unique patterns of hippocampal shape changes. Our findings encourage future studies to elucidate the underlying mechanism of hippocampal morphometric abnormalities in INPH patients. Changes in overall shape may contribute to the distinctive gait abnormalities associated with INPH.