MRI Evaluation and Reporting in Suspected and Established Idiopathic Normal Pressure Hydrocephalus, AJR Expert Panel Review.

This AJR Expert Panel Narrative Review summarizes MRI features of idiopathic normal pressure hydrocephalus (iNPH) and their utility in various clinical scenarios, describes imaging features suggestive of alternate or co-pathology, and provides a framework for reporting such findings. iNPH is characterized by gait impairment, cognitive decline, and urinary incontinence that may be improved with CSF shunting. Imaging is an important part of the diagnostic assessment for iNPH by identifying findings supportive of a diagnosis of iNPH or of alternate diagnoses or co-pathology. Although MRI features of iNPH have been proposed, these features' utility for diagnosis, prognosis, and treatment monitoring have varied among studies. The imaging assessment for suspected iNPH should include an unenhanced brain MRI examination incorporating, among other sequences, a 3D-T1weighted sequence. Key imaging features supportive of an iNPH diagnosis include: ventriculomegaly, high-convexity narrowed sulci, and enlarged Sylvian fissures (collectively termed disproportionately enlarged subarachnoid space hydrocephalus [DESH]), along with cerebral aqueduct patency. Incidentally detected findings of iNPH may be summarized in the report impression as "findings supportive of a diagnosis of iNPH in the appropriate clinical context." This article concludes with consensus statements summarizing MRI protocols and findings to report in the diagnostic assessment and treatment monitoring of iNPH.