Evans' Index and Frontal and Occipital Horn Ratio in Correlation to Volumetric Data of Lateral Ventricles in...

Evans' Index (EI) and Frontal and Occipital Horn Ratio (FOHR) are routinely used in screening for enlargement of the ventricular system. However, both lack epidemiological definition of normal values in adults. In a representative, randomized sample of adult normal population in Germany we studied the correlation of lateral ventricle volumes with EI and FOHR to evaluate the performance of pre-established cutoff values of EI > 0.3 and FOHR > 0.37, and to introduce age- and sex-specific thresholds, which for FOHR do not yet exist in adults.

In a population-based sample of 3058 subjects of the "Study of Health in Pomerania" (SHIP), aged 21-90 years, brain imaging with T1 weighted MPRAGE with 1 mm isotropic voxel-size was obtained. We semiautomatically determined the volumes of the lateral ventricles and manually performed measurements to calculate EI and FOHR for every individual. Besides descriptive statistics, ROC analyses were carried out to determine test performance of both parameters. Negative and positive predictive values were derived from contingency analyses.

Average values were 0.257 ± 0.025 for EI and 0.363 ± 0.024 for FOHR, with sex- and age-depending differences. Using the established cut-off value of EI > 0.3, this index achieved high specificity of 97.1% and moderate sensitivity of 55.3% for diagnosing ventricular enlargement. Using a threshold of > 0.4, FOHR achieved a specificity of 93.4%, and higher sensitivity of 81.4%. FOHR showed stronger correlation with actual lateral ventricle volumes, as compared to EI (r_{s FOHR} = 0.741 vs. r_{s EI} = 0.656; p < 0.001).

For the first time, EI and FOHR were evaluated in a reasonable sized, randomized, representative sample of normal adult population in Germany, and were confirmed as useful screening tools in the diagnosis of ventricular enlargement. We introduce a cut-off value of > 0.4 for FOHR in adults, with emphasis on specific caveats.