MRI markers of idiopathic normal pressure hydrocephalus in a population study with 791 participants: Exploring reference values and associations.

PurposeEpidemiological studies on idiopathic normal pressure hydrocephalus (iNPH) imaging markers and their normal values are scarce. This population-based study aimed to analyze several morphologic and volumetric iNPH-related imaging markers in a large sample, determining their distribution, diagnostic accuracy, suggested cut-offs, and associations with iNPH symptoms.MethodsThis cross-sectional study included 791 70 year olds, 40 with radiologically probable iNPH (iNPHRadiol) and 751 without iNPH features (reference). MRI measures included Evans index (EI), z-EI, brain per ventricle ratio at anterior (BVRAC) and posterior commissures (BVRPC), sulcal compression, Sylvian fissure enlargement, callosal angle, diameter of temporal horns, 3rd and 4th ventricles, midbrain, and pons. Volumes of ventricles, corpus callosum, and brainstem were computed using automated segmentation. ROC analysis determined imaging markers' cut-offs. Symptoms were evaluated clinically and through self-report.ResultsIn the reference group, median values (95% CI) for imaging markers were as follows: EI: 0.27 (0.26-0.27), z-EI: 0.28 (0.26-0.31), BVRAC: 1.69 (1.48-1.90), and BVRPC: 2.66 (2.24-3.27). Most imaging markers differed significantly between iNPHRadiol and the reference. Lateral ventricle volumes correlated better with z-EI and BVR than EI (Rs > 0.81 vs 0.68). Optimal cut-off values for z-EI, and BVRAC and BVRPC for distinguishing iNPHRadiol were 0.32, 1.36, and 1.83, respectively. Clinical symptoms correlated moderately with imaging markers (Rs < 0.49 for iNPHRadiol, p < .01).ConclusionsWe report population-based reference values and propose cut-offs for iNPH-related imaging markers and volumetric measurements. Z-EI and BVR are likely superior markers for assessing ventricular enlargement in iNPH. Imaging markers of iNPH correlate moderately with iNPH symptoms.