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Abstract
Background: The Evans Index (EI), which is the ratio of the largest transverse diameter of the frontal horns to the largest internal diameter of the skull at the same axial level, is the most commonly used linear radiological ratio of ventricular enlargement used routinely in reporting of cranial CT scans. Globally, 0.3 has been used as a threshold for ventriculomegaly, and is incorporated in international guidelines for idiopathic normal pressure hydrocephalus (NPH) diagnosis. However, large-scale normative studies have shown that EI steadily rises with age and is systematically higher for males than females, making it insufficient to have a single cut-off threshold, without age and sex-specific reference values. There are no population specific normative CT EI data for Pakistani adults and Pakistani clinicians use data obtained from different ethnic populations. Objectives: To introduce different age and sex-specific normative values of Evans index for healthy population of Pakistan, and to determine the effects of age and sex on EI. Method: A prospective cross-section study was carried out in Idrees Hospital, Sialkot, Pakistan for 6 months. There were 140 participants in this study and they were healthy adults, ages 18–80 years, seven age groups (n = 10 for each sex group). Results: In healthy Pakistani adults (140 adults; 70 male and 70 female; age range 18–80 years) the mean Evans Index (EI) overall was 0.27 (SD = 0.03), and was not different between male and female groups. When the scores of EI were compared across the ages, a positive correlation was observed and it was found to be statistically significant (rs = 0.549, p < 0.001), with mean scores showing increase gradually from 0.25 (SD = 0.01) in the youngest age group (18-20 years) to 0.30 (SD = 0.04) in the oldest age group (71-80 years). There was no significant difference between the EI mean scores of the males and the females in the sample (Mann-Whitney U = 2216.5, p = 0.327), and the mean scores were identical for the males and females across both sex groups. Conclusions: In this study, the normative CT value of Evans Index is set for the first time in a healthy adult population of Pakistan using an age stratification model. The EI increases with age and the influence of sex is not independent in this cohort. This indicates that the use of a single EI cut-off of ≥ 0.3 may not be clinically relevant for younger Pakistani adults; age-dependent EI reference standards should be used in the routine interpretation of cranial CT scans for NPH screening in Pakistan