Abstract
With an ever-growing aging population, the prevalence of normal pressure hydrocephalus (NPH) is increasing. Clinical symptoms of NPH include cognitive impairment, gait disturbance, and urinary incontinence. Surgery can improve symptoms, which leads to the disease's alternative name: treatable dementia. The Evans index (EI), defined as the ratio of the maximal width of the frontal horns to the maximum inner skull diameter, is the most commonly used index to indirectly assess the condition of the ventricles in NPH patients. EI measurement is simple, fast, and does not require any special software; in clinical practice, an EI >0.3 is the criterion for ventricular enlargement. However, EI's measurement methods, threshold setting, correlation with ventricle volume, and even its clinical value has been questioned. Based on the EI, the z-EI and anteroposterior diameter of the lateral ventricle index were derived and are discussed in this review.
Highlights
Normal pressure hydrocephalus (NPH) refers to a condition in which the cerebrospinal fluid (CSF) pressure is normal, but the hydrocephalus in the ventricular system is dilated
The comparison of Evans index (EI) results using different planes and angles can lead to differences, which may be due to the different measurement methods rather than changes in the ventricle (Ryska et al, 2021)
The measurement of EI is affected by different imaging planes and angles, and its normal range varies depending on both age and sex
Summary
Normal pressure hydrocephalus (NPH) refers to a condition in which the cerebrospinal fluid (CSF) pressure is normal, but the hydrocephalus in the ventricular system is dilated. As more than 80% of patients can be treated with surgery to improve their symptoms, including the improvement of cognitive impairment (Jaraj et al, 2016), it is known as treatable dementia (Nakajima et al, 2021). It mostly affects the elderly (Zaccaria et al, 2020), and according to two recent epidemiological surveys in Sweden (Jaraj et al, 2014; Andersson et al, 2019), the prevalence of NPH among 65-year-olds was 3.7%. EI (2) EI measurement method (3) Threshold setting of the EI (4) Correlation between the EI and VV (5) Clinical value of the EI (6) Alternative index to the EI.
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