Citation, DOI, disclosures and article data
Citation:
Venkatesh M, Yap J, Gaillard F, et al. Evans index. Reference article, Radiopaedia.org (Accessed on 16 Apr 2024) https://doi.org/10.53347/rID-26125
The Evans index can be used as a marker of ventriculomegaly.
It is useful as a marker of ventricular volume and thus has been proposed as a helpful biomarker in the diagnosis of normal pressure hydrocephalus (NPH) 1. Unfortunately, it is a very rough marker of ventriculomegaly and varies greatly depending on the location and angle of the slice 2. As such, the Evans index has little role to play in day-to-day reporting 4.
Evans index is the ratio of the maximum width of the frontal horns of the lateral ventricles and the maximal internal diameter of the skull at the same level employed in axial CT and MRI images.
Interpretation of the Evans index is as follows 5:
The ratio can be higher in a normal healthy elderly individual, and varies with age and sex 3.
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History and etymology
The ratio was first proposed by William A Evans, Jr, in 1942 5.
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1. Ng S, Low A, Tang K, Chan Y, Kwok R. Value of Quantitative MRI Biomarkers (Evans' Index, Aqueductal Flow Rate, and Apparent Diffusion Coefficient) in Idiopathic Normal Pressure Hydrocephalus. J Magn Reson Imaging. 2009;30(4):708-15. doi:10.1002/jmri.21865 - Pubmed
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2. Toma A, Holl E, Kitchen N, Watkins L. Evans' Index Revisited: The Need for an Alternative in Normal Pressure Hydrocephalus. Neurosurgery. 2011;68(4):939-44. doi:10.1227/NEU.0b013e318208f5e0 - Pubmed
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3. Brix M, Westman E, Simmons A et al. The Evans' Index Revisited: New Cut-Off Levels for Use in Radiological Assessment of Ventricular Enlargement in the Elderly. Eur J Radiol. 2017;95:28-32. doi:10.1016/j.ejrad.2017.07.013 - Pubmed
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4. Neikter J, Agerskov S, Hellström P et al. Ventricular Volume Is More Strongly Associated with Clinical Improvement Than the Evans Index After Shunting in Idiopathic Normal Pressure Hydrocephalus. AJNR Am J Neuroradiol. 2020;41(7):1187-92. doi:10.3174/ajnr.A6620 - Pubmed
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5. Evans W. An Encephalographic Ratio for Estimating Ventricular Enlargement and Cerebral Atrophy. Arch NeurPsych. 1942;47(6):931. doi:10.1001/archneurpsyc.1942.02290060069004
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