Freddi Segal-Gidan is Director of the Rancho Los Amigos/University of Southern California (USC) Alzheimer’s Disease Center and Assistant Clinical Professor in the departments of Neurology and Family Medicine at Keck School of Medicine, USC, and in Gerontology at L. Davis School of Gerontology at USC, Los Angeles.
NEUROIMAGING Brain neuroimaging with CT or MRI is essential to the initial investigation and diagnostic evaluation of suspected iNPH. Neuroimaging is not diagnostic in itself, but the findings are important both to support a suspected diagnosis of iNPH and to exclude other conditions that could cause similar findings or contribute to the symptoms (eg, stroke or tumor).
The key finding is enlargement of the lateral ventricles (ventriculomegaly) disproportionate to the degree of cortical atrophy (see Figure 1). Ventricular dilatation is characterized by rounding of the contour of the ventricles with a widened third ventricle. Normal volume of brain parenchyma is evidenced by the absence of sulci widening, which would be seen in the presence of cortical atrophy and the absence of obscured sulci. White matter changes, seen as periventricular white matter hyperintensity on MRI, has also been noted frequently on imaging consistent with iNPH.14 On MRI, a marked CSF flow void in the aqueduct of Sylvius and fourth ventricle, called a flow void, is usually seen.15
The Evans ratio, calculated by dividing the maximum width of the ventricular frontal horns on imaging by the widest skull diameter, is one criteria for diagnosis of iNPH on neuroimaging. An Evans ratio greater than 0.3 (signifying ventriculomegaly), within the appropriate clinical context, is considered indicative of iNPH.14,16
