Background: The Evans’ index is an indirect marker of ventricular volume helpful in the diagnosis of hydrocephalus. Data on normal or baseline
value for the Evans’ index for the Thai population are not available.
Objective: The primary objective of the present study was to establish gender- and age-appropriate normal or baseline value of Evans’ index for the Thai population. The secondary objective was to assess the correlation between Evans’ index derived from computed tomography (CT) brain and magnetic resonance imaging (MRI) of the brain.

Material and Methods: The present study was a retrospective descriptive study conducted between January and June 2020 at the Vajira Hospital. The authors included data from 711 patients with normal brain CT, of these, normal MRI were also available for 40 subjects. Patients with intracranial pathology on CT or MRI brain and neurological disorders were excluded. The Evans’ index was defined as the ratio of the maximum width of the frontal horns of the lateral ventricle and the maximal internal diameter of the skull at the same level.

Results: Of the 711 patients, 355 (49.9%) were male and 356 (50.1%) were female, their age ranged from four days to 94 years, and the mean value of Evans’ index was 0.2591±0.0355. Evans’ index increased with age and was slightly higher among males. The difference in Evans’ index values between male and female patients was significant only in individuals aged 61 to 70 years and older than 80 years. The Evans’ index calculated from CT and MRI brain showed good correlation with an ICC of 0.919 (95% CI 0.851 to 0.956).

Conclusion: Data from the present study concur with the Evans’ index cutoff value for hydrocephalus as greater than 0.3 for age 70 years and younger. For individuals with age of 70 years and older, the cutoff value should be 0.34.

Keywords: Evans’ index; Hydrocephalus; Normal pressure hydrocephalus (NPH); Thailand population

DOI: 10.35755/jmedassocthai.2022.06.13321

Received 14 October 2021 | Revised 20 April 2022 | Accepted 20 April 2022