Jaraj D, Agerskov A, Rabiei K et al. Vascular risk factors in suspected normal pressure hydrocephalus. A population based study. Neurology 2016; 86: 592-599
Authors found that hypertension, white matter lesions on MRI and diabetes were related to clinical and imaging features of NPH suggesting vascuar mechanisms;
Graff-Radford NR. Is normal pressure hydrocephalus becoming less idiopathic? Neurology 2016; 86: 588-89.
Dr. Graff Radford discusses that the problem usually cited, resistance to CSF outflow, is problematic as an etiology as some patients with normal CSF outflow resistance also present with hydrocephalus. He points out that more than 10 %of patients with iNPH have congenital hydrocephalus, and more than 10 % have a head size above the 98th percentile.
Ventricular pulse pressure is related to iNPH, and ligating the choroid plexus in dogs unilaterally (prventing pulse pressure) prevents hydrocephalus in that but not the other ventricle.
In a human study, patients with iNPH but without an absorption problem underwent shunting; these patients had severe vascular risk factors. They improved with shunting. The small study (n=14) was blinded and randomized sothe control group had their shunts ligated for three months in the neck and only improved after un-ligation.
He regards the question of vascular risk factors as etiologic to be unresolved.