Which imaging metric quantifies ventriculomegaly in suspected hydrocephalus?

• A. Fazekas scale
• B. Evans index
• C. Fisher index
• D. Hounsfield index

Answer: (B)

In suspected hydrocephalus, you want a metric that directly quantifies how enlarged the ventricular system is on a routine CT or MRI. The Evans index does that by comparing the width of the frontal horns of the lateral ventricles to the inner width of the skull at the same level. You measure the maximum frontal horn width and divide by the maximum inner skull width; a value around 0.3 or higher indicates ventriculomegaly. This approach is simple, reproducible, and widely used in clinical practice to assess ventricular enlargement.

Other options don’t measure ventricular size: the Fazekas scale assesses white matter changes, not ventricles; the Fisher index is a grading system for subarachnoid hemorrhage on CT; and Hounsfield units reflect tissue density, not the extent of ventriculomegaly.