Diagnosis of Normal-Pressure Hydrocephalus: Use of Traditional Measures in the Era of Volumetric MR Imaging

Abstract

Purpose To assess the diagnostic performance of the callosal angle (CA) and Evans index (EI) measures and to determine their role versus automated volumetric methods in clinical radiology. Materials and Methods Magnetic resonance (MR) examinations performed before surgery (within 1-5 months of the MR examination) in 36 shunt-responsive patients with normal-pressure hydrocephalus (NPH; mean age, 75 years; age range, 58-87 years; 26 men, 10 women) and MR examinations of age- and sex-matched patients with Alzheimer disease (n = 34) and healthy control volunteers (n = 36) were studied. Three blinded observers independently measured EI and CA for each patient. Volumetric segmentation of global gray matter, white matter, ventricles, and hippocampi was performed by using software. These measures were tested by using multivariable logistic regression models to determine which combination of metrics is most accurate in diagnosis. Results The model that used CA and EI demonstrated 89.6%-93.4% accuracy and average area under the curve of 0.96 in differentiating patients with NPH from patients without NPH (ie, Alzheimer disease and healthy control). The regression model that used volumetric predictors of gray matter and white matter was 94.3% accurate. Conclusion CA and EI may serve as a screening tool to help the radiologist differentiate patients with NPH from patients without NPH, which would allow for designation of patients for further volumetric assessment. ^© RSNA, 2017.

Figure 1:

By using MPRAGE sequences, a coronal plane was obtained at the level of the posterior commissure from each observer’s best approximation (blue and red lines, left), with plane oriented 90° to anterior-posterior commissure line. By using the plane at this level, CA was determined (red arrows, middle) as the angle between the superior borders of the lateral ventricles. EI was determined on transaxial view by measuring the largest left-to-right width of the frontal horns divided by the largest left-to-right extent the skull (red arrows, right).

Figure 2:

Sample sagittal (left), posterior coronal (middle), and midtransaxial (right) segmentation masks overlaid on T1-weighted MR images of shunt-responsive NPH, definitive AD, and HC volunteers. These images show gray matter (in red), white matter (in yellow), ventricular (in blue), and hippocampal (in green) regions.

Figure 3:

Scatterplot demonstrates the cutoff values of CA and EI that separate patients with NPH from patients who do not have NPH (ie, patients with AD and HC volunteers).

Figure 4:

Box-and-whisker plots of segmentation parameters across the three patient groups. The plots show, A, gray matter, B, white matter, C, ventricles, and, D, hippocampi.