LAUSR

OBJECTIVE Idiopathic normal pressure hydrocephalus (iNPH) is characterized by ventricular enlargement that deforms the corpus callosum, making the callosal angle (CA) small. The authors aimed to evaluate the clinical usefulness of the CA in different planes in iNPH. METHODS Forty patients with iNPH were included in the study. As a control group, 241 patients with other neurological diseases and 50 healthy controls were included. The subjects had been seen at the authors' institutions from 2010 to 2020. The Timed Up and Go (TUG) test total time and Mini-Mental State Examination (MMSE) total score were evaluated. CAs were measured in the axial plane at the splenium and genu and in the coronal plane at the anterior commissure and posterior commissure by using 3-dimensional T1-weighted MR images. As other hydrocephalus parameters, the Evans index, frontal-occipital horn ratio, and third ventricular width were also measured in patients with iNPH. Associations between each CA or hydrocephalus parameter and clinical parameters were evaluated. The classification efficacy of each CA in differentiating between iNPH and other neurological diseases and healthy controls was evaluated. RESULTS The CA at the splenium, but no other hydrocephalus parameters, was correlated with TUG total time or MMSE total score in patients with iNPH. Receiver operating characteristic analysis showed that a CA of 71.1° at the splenium has 90.0% sensitivity and 89.0% specificity in discriminating iNPH from other neurological diseases and healthy controls. Probabilistic tractography analysis showed that neuronal fibers via the splenium connect the superior parietal lobules, temporal lobes, and occipital lobes. CONCLUSIONS The study results suggest that interhemispheric disconnections at the splenium are, at least in part, responsible for gait and cognitive disturbance in iNPH. The CA at the splenium is a unique morphological feature that correlates with gait and cognition in iNPH, and it is useful for discriminating iNPH from other neurological diseases and healthy controls.