Evan's index is the ratio of maximum width of the frontal horns to the maximum width of the inner table of the cranium. An Evan's index more than 0.31 indicates hydrocephalus. Patients with suspected<unk>  should have typical symptoms in addition to ventricular enlargement on neuroimaging. The international evidenced-based diagnostic criteria for primary<unk>  are: * Gradual onset after age 40 years, symptoms duration of ≥ 3–6 months, clinical evidence of gait or balance impairment, and impairment of cognition or urinary incontinence * Imaging from magnetic resonance imaging (MRI) or computed tomography (CT) is needed to demonstrate enlarged ventricles and no macroscopic obstruction to cerebrospinal fluid flow. Imaging should show an enlargement to at least one of the temporal horns of lateral ventricles, and impingement against the falx cerebri resulting in a callosal angle ≤ 90° on the coronal view, showing evidence of altered brain water content, or<unk>  active flow (which is referred to as "flow void") at the cerebral aqueduct and fourth ventricle. +Typical imaging findings in<unk>  versus brain atrophy. 335px 333px<unk>  Brain atrophy Preferable projection Coronal plane at the level of the posterior commissure of the brain. Modality in this example CT MRI CSF spaces over the convexity near the vertex (red ellipse 20px) Narrowed convexity ("tight convexity") as well as medial cisterns Widened vertex (red arrow) and medial cisterns (green arrow) Callosal angle (blue ) Acute angle Obtuse angle Most likely cause of leucoaraiosis (periventricular signal alterations, blue arrows 25px) Transependymal cerebrospinal fluid diapedesis Vascular encephalopathy, in this case suggested by unilateral occurrence MRI scans are preferred. The distinction between<unk>  and enlarged ventricular size by cerebral atrophy is difficult to ascertain. Up to 80% of cases are unrecognized and untreated due to difficulty of diagnosis. Imaging should also reveal the absence of any cerebral mass lesions or any signs of obstructions. Although all patients with<unk>  have enlarged ventricles, not all elderly patients with enlarged ventricles have primary<unk> . Cerebral atrophy can cause enlarged ventricles, as well, and is referred to as hydrocephalus ex vacuo. The Miller Fisher test involves a high-volume lumbar puncture (LP) with removal of 30–50 ml of CSF. Gait and cognitive function are typically tested just before and within 2–3 hours after the LP to assess for signs of symptomatic improvement. The CSF infusion test and the lumbar test are similar tests to Miller Fisher test. The tests have a positive predictive value over 90%, but a negative predictive value less than 50%. The LP should show<unk>  or mildly elevated CSF<unk> . CSF should have<unk>  cell contents, glucose levels, and protein levels.
Normal pressure hydrocephalus
Low pressure hydrocephalus
Lewy body dementias
Early-onset Alzheimer's disease
Multiple system atrophy
Frontotemporal dementia
Vascular dementia
Dementia with Lewy bodies