Normal-pressure hydrocephalus: A critical review

Abstract

Normal-pressure hydrocephalus (NPH) is a potentially reversible syndrome characterized by enlarged cerebral ventricles (ventriculomegaly), cognitive impairment, gait apraxia and urinary incontinence. A critical review of the concept, pathophysiology, diagnosis, and treatment of both idiopathic and secondary NPH was conducted. We searched Medline and PubMed databases from January 2012 to December 2018 using the keywords "normal-pressure hydrocephalus" / "idiopathic normal-pressure hydrocephalus" / "secondary normal-pressure hydrocephalus" / "NPH" / "ventriculoperitoneal shunt". The initial search produced 341 hits. After careful selection, a total of 54 articles were chosen and additional relevant studies were included during the process of writing this article. NPH is an important cause of potentially reversible dementia, frequent falls and recurrent urinary infections in the elderly. The clinical and imaging features of NPH may be incomplete or nonspecific, posing a diagnostic challenge for medical doctors and often requiring expert assessment to minimize unsuccessful surgical treatments. Recent advances resulting from the use of non-invasive MRI methods for quantifying cerebral blood flow, in particular arterial spin-labeling (ASL), and the frequent association of NPH and obstructive sleep apnea (OSA), offer new avenues to understand and treat NPH.

Keywords: cerebral blood flow; falls; incontinence; normal-pressure hydrocephalus; reversible dementia; spinal tap test.

Figure 1. Neuroimaging in NPH (A) Axial FLAIR MRI scan showing a significant ventriculomegaly with increased Evans Index, the ratio of maximum width of the frontal horns of the lateral ventricles and maximal internal diameter of skull at the same level on axial CT or MRI images. In this case, Evans index is 0.39 (abnormal > 0.3) (B) T1-weighted coronal gadolinium-enhanced MRI scan showing reduced callosal angle. (C) Axial FLAIR MRI scan revealing enlarged lateral ventricles with bright signal in the surrounding white matter, suggestive of transependymal edema. (D) Axial FLAIR MRI showing narrowing of the sulci and subarachnoid spaces over the high convexity and midline surface in the frontoparietal regions.

Figure 2. An example of ASL-MRI illustrating a positive correlation between enhanced CBF and clinical improvement after large-volume spinal tap (unpublished data).