Normative Evans index values in the Turkish adult population: an age- and sex-stratified MRI study.

PURPOSE: The Evans Index (EI) is a widely used radiological parameter for the assessment of ventriculomegaly and normal pressure hydrocephalus, but its values may vary according to demographic characteristics. The aim of this study was to determine EI normative reference values in the Turkish adult population and to evaluate the relationship of these values with age and sex.

METHODS

The study included 600 individuals with normal cranial magnetic resonance imaging (MRI) findings. The individuals were divided into three age groups (18-39, 40-59, 60-77 years) with 100 women and 100 men in each group. EI was calculated by measuring frontal horn width (FHW) and maximum internal skull diameter (MISD) on T2-weighted axial sections (EI = FHW/MISD).

RESULTS

The mean EI value for the entire sample was found to be 0.243 ± 0.02. FHW, MISD and EI values were significantly higher in males than in females (p < 0.05). In the age group analysis, FHW values remained stable, but due to the significant decrease in MISD with age (r= - 0.271), EI values were found to be higher in older age groups and plateaued from the age of 40 onwards. The main difference was determined to be between the 18-39 age group and the other groups (p = 0.002).

CONCLUSION

The normative EI values determined for the Turkish population are below the 0.30 threshold found in the literature. It has been determined that the age-related increase in the index may be associated with cranial changes rather than ventricular dilatation and stabilises after the age of 40. These findings emphasise the importance of population-specific and age-sensitive reference ranges in clinical assessments.