Morphometric evaluation of Evans Index in healthy North Indian Adults: establishing normative MRI-based reference values.

Background: The Evans Index (EI) is a practical radiological tool used to assess ventricular size; however, its normative values remain insufficiently defined across diverse populations. This study aimed to establish normative EI values in a healthy North Indian adult population and investigate age and sex-based differences in ventricular morphometry.

Materials and methods: A cross-sectional magnetic resonance imaging (MRI)-based study was conducted on 142 neurologically healthy North Indian adults (79 females and 63 males; age range: 18-72 years). Axial T2-weighted images acquired on a 1.5 Tesla MRI system were analyzed to measure frontal horn width (FHW) and transverse inner diameter of the skull (TIDS). The Evans Index was calculated as the ratio of FHW to TIDS. Statistical analyses using SPSS 29.0 included Welch's t-tests for sex comparisons, Spearman's correlation, and binary logistic regression to evaluate the association between cranial measurements and age and biological sex.

Results: The mean age of participants was 37.4 years. The overall average values were FHW = 31.5 mm, TIDS = 122.4 mm, and EI = 0.257. Males exhibited significantly higher mean values than females for EI (0.265 vs 0.251; p < 0.001). Correlation analysis revealed a strong positive correlation between FHW and EI (rho = 0.866; p < 0.001). Logistic regression identified FHW as the strongest predictor of sex (OR: 1.82, p < 0.001). Model performance parameters included sensitivity of 0.746, specificity of 0.861, and AUC of 0.81.

Conclusions: This study establishes normative Evans Index values for a healthy North Indian population and demonstrates significant sex differences in cranial morphometric parameters. FHW and EI are useful predictors of biological sex with clinical relevance.