Measurement of ventricular size: Reliability of the frontal and occipital horn ratio compared to subjective assessment

Introduction: The frontal and occipital horn ration (FOR) has recently been described as a simple, linear measurement of ventricular size that correla tes very well with ventricular volume. This study further characterizes the measurement properties of the FOR by investigating its interobserver relia bility and comparing it to a subjective assessment of ventricular size. Met hods: Axial images (CT and MR) of children with hydrocephalus taken before and after third ventriculostomy were reviewed by 4 independent observers. T wo observers were blinded to patient identity and clinical status and 2 obs ervers were nonblinded. Each observer independently recorded linear measure ments from which the FOR was calculated for each image. Each reviewer also made a separate subjective assessment of the degree of hydrocephalus on a g -point adjectival scale. Reliability was calculated using a repeated-measur es analysis of variance (ANOVA) and an intraclass correlation coefficient ( ICC) with random image and observer effects. Results: There were 120 separa te observations (4 observers, 30 images). The FOR ranged from 0.33 to 0.75 (mean 0.55, standard deviation 0.11). The reliability coefficient was 0.93 (95% confidence interval, CI 0.80-0.97) between the 2 blinded observers and 0.98 (95% CI, 0.95-0.99) between the 2 nonblinded observer. The overall in terobserver reliability for all 4 observers was 0.95 (95% CI 0.92-0.98). Th e mean FOR for each observer was very similar, regardless of the observer's blinding status. However, the reliability of the observers' subjective ass essment of the hydrocephalus was much lower (ICC = 0.77, 95% CI 0.60-0.88). Conclusions: The FOR demonstrates excellent interobserver reliability (>0. 9) and was superior to subjective assessments of hydrocephalus. In this stu dy, excellent reliability was maintained regardless of the blinding status of the observers. This further demonstrates the properties of the FOR as a simple and reproducible measure of ventricular size. It is suitable for use in clinical studies, possibly even in situations in which observer blindin g is not possible.