Clinical Tools & Calculators

Evans Index

For educational use. This tool is intended for reference and education. All care decisions require a direct clinical assessment of the patient and independent verification of doses and values by the treating team. The calculation runs locally in your browser, no patient data is sent to any server.

Evans Index

The ratio of the maximum width of the frontal horns of the lateral ventricles to the maximum internal skull diameter on the same axial slice. Used to assess ventriculomegaly. Values > 0.30 are considered abnormal in adults, paediatric thresholds vary by age.

0.29
Evans Index
Normal (≤ 0.30 in adults)‎
Source: Evans WA Jr. An encephalographic ratio for estimating ventricular enlargement and cerebral atrophy. Arch Neurol Psychiatry 1942;47(6):931–937.
On the history of the Evans Index (review): Fleuren KJR, Koehler PJ, Hoff EI. The History of the Evans Index. Eur Neurol 2025;88(2):92–96. Article (Karger) · Evans' original 1942 article (JAMA Network)
Modern interpretation: Toma AK, et al. Evans' index revisited: the need for an alternative in normal pressure hydrocephalus. Neurosurgery 2011;68(4):939–44. PMID 21221031 · doi:10.1227/NEU.0b013e318208f5e0

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