Normative values for Evan's index on CT scan for apparently healthy individuals

Limited data are available from India that describe the normative volume and size of ventricular system. We add our experience with normative values of Evan's index to measure the ventricular size on CT scan in apparently healthy individuals. A total of 326 patients were included in the study, in whom brain CT scan was performed for various indications and it was apparently normal. Evan's index ratio was obtained by measuring maximum frontal horn width to the maximum transverse diameter of the inner table in the same section. The data entry and statistical analysis were done using StatsDirect® version-3. Data were expressed as mean, standard deviation, actual numbers, and percentages. We divided the Evan's index into two categories, <0.3 and >0.3, which indicates ventriculomegaly to find out % of abnormality. The mean Evan's index in these patients was 0.25 ± 0.02. There was no trend in Evan's index with increasing age. It was appreciated that there was not much variation in calculation of Evan's index from CT scan. It was found that Evan's index could be calculated fairly accurately by multiple observers, which could be appreciated in the form of very small standard deviations. In summary, the normative values of Evan's index in a group of persons were similar to as described in literature. Less than 5% of patients were having ventriculomegaly but there were no clinical symptoms related to ventriculomegaly.