Good Correlation between CT-Measured Z-Evans’ Index and CT Volumetric of Ventricular System in Patients with iNPH Treated by Cerebrospinal Fluid Shunting

Background: Patients with idiopathic normal pressure hydrocephalus (iNPH) demonstrated an increase in the volume of lateral ventricles oriented along the Z-axial axis, as opposed to the X-axial axis. Objective: To determine which computed tomography (CT)-measured X-Evans’ index and Z-Evans’ index, exhibit a stronger correlation with CT-derived ventricular volume both before and after shunting procedures. Additionally, a comparative examination between those with iNPH characterized by disproportionate enlargement of subarachnoid space hydrocephalus (DESH) and those without DESH features. Materials and Methods: The present study enrolled forty-three iNPH patients who underwent shunting between April 2013 and April 2016. The initial screening involved a thorough review of pre-shunting CT images, leading to the categorization of patients into two distinct groups, those with DESH and without DESH features. Results: Both the X-Evans’ index and Z-Evans’ index exhibited a noteworthy correlation with ventricular volume, substantiated by correlation coefficients (r) of 0.777 (p<0.001) and 0.876 (p<0.001), respectively. Notably, the correlation between the change in CT ventricular volume and the change in Z-Evans’ index was more conspicuous in the overall patient cohort (r=0.730, p<0.001) than X-Evans’ index change (r=0.599, p<0.001). This tendency was particularly discernible within the DESH group, where the correlation with Z-Evans’ index (r=0.826, p<0.001). Conclusion: The Z-Evans’ index emerged as a more effective representation of ventricular volume compared to the X-Evans’ index in the entirety of the iNPH patient cohort. In contrast, during the subsequent CT follow-up, the change in X-Evans’ index exhibited superior efficacy in capturing the corresponding alterations in ventricular volume.