![]() Evans retrospectively analyzed the 53 encephalograms of normal patients done at the Children's Hospital of Michigan and Harper Hospital and concluded that the ratio of the transverse diameter of the anterior horns to the internal diameter of the skull could be used as an index to evaluate ventricle size. First proposed by Evans in 1942, it has been used to indirectly assess the expansion of the ventricular system in encephalography ( Evans, 1942). The Evans index (EI) is defined as the ratio of the maximal width of the frontal horns to the maximum inner skull diameter. This means that the prevalence of NPH increases with age. More importantly, in these two studies, the prevalence of NPH disease in elderly people over 80 years old was as high as 5.9% and 8.9%. ![]() 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%. However, 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 also known as treatable dementia ( Nakajima et al., 2021). Its clinical manifestations include gait disorders, cognitive disorders, and urinary incontinence ( Adams et al., 1965). 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. Based on the EI, the z-EI and anteroposterior diameter of the lateral ventricle index were derived and are discussed in this review. However, EI's measurement methods, threshold setting, correlation with ventricle volume, and even its clinical value has been questioned. 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. ![]() 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. Surgery can improve symptoms, which leads to the disease's alternative name: treatable dementia. Clinical symptoms of NPH include cognitive impairment, gait disturbance, and urinary incontinence. With an ever-growing aging population, the prevalence of normal pressure hydrocephalus (NPH) is increasing. Department of Radiology, The First Affiliated Hospital of Shenzhen University, Health Science Center, Shenzhen University, Shenzhen Second People's Hospital, Shenzhen, China. ![]()
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