Radiographic Evaluation of Normal Pressure Hydrocephalus

Normal pressure hydrocephalus (NPH) is a clinical syndrome of a gait disorder, cognitive impairment, and urinary incontinence that also has characteristic imaging features. This article provides an overview of the radiographic evaluation and imaging features of NPH.

Ventriculomegaly is an overarching imaging feature of NPH, although it is nonspecific. More specific imaging features have been described in association with NPH subtypes. Patients with idiopathic NPH commonly have features of ventriculomegaly, high-convexity tight sulci, and enlarged sylvian fissures. Patients with delayed-onset congenital NPH have features of marked ventriculomegaly, without extraventricular hydrocephalus, and may have stenosis or obstruction of the cerebral aqueduct. Evaluation of CSF dynamics, patterns of radiotracer uptake on positron emission tomography (PET), and patterns of brain stiffness on MR elastography can help to differentiate idiopathic NPH from secondary NPH or a neurodegenerative process.

Imaging features of disproportionately enlarged subarachnoid space hydrocephalus are important to recognize as they are part of the diagnostic criteria for idiopathic NPH and aid in differentiating NPH from a neurodegenerative process. Evaluation of CSF dynamics, patterns of fludeoxyglucose (FDG) uptake, and patterns of brain stiffness may aid in the evaluation of challenging cases that lack typical clinical and structural radiographic features.