Evans Index (Ventricular Enlargement)
Evans index: maximum frontal-horn width / inner-skull (biparietal) diameter on the same axial slice; > 0.30 defines ventricular enlargement (radiologic hydrocephalus threshold).
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Maximum frontal-horn width
- 45 mm
- Maximum inner-skull (biparietal) diameter
- 140 mm
Result: Evans index 0.32 — ventricular enlargement (> 0.30 — radiologic hydrocephalus threshold).
The tool opens with these values already filled in. Replace them with your own.
What the result means
- <= 0.25
- Within normal range.
- 0.25-0.30
- Borderline.
- > 0.30
- Ventricular enlargement (radiologic hydrocephalus threshold). It does not distinguish atrophy from CSF-dynamics disturbance. A ratio, not a diagnosis.
What you enter
- Maximum frontal-horn width
- Maximum inner-skull (biparietal) diameter
How this is calculated
Evans WA Jr. An encephalographic ratio for estimating ventricular enlargement and cerebral atrophy. Arch Neurol Psychiatry. 1942;47(6):931-937. (Modern radiologic threshold > 0.30: Frontiers Aging Neurosci. 2021;13:783092.) Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.