Many patients have none of the above predisposing conditions listed above. The pathophysiology of INPH is still undecided. There is a frequent co- ocurrence of INPH and vascular subcortical encephalopathy. Frequent and severe periventricular lesions and DWMIs were noted in INPH but no direct causal relationship is supported. Krauss postulated a parenchymal compliance problem.
Vascular lesions reduce elastic properties of cerebral white matter and alter tissue strength.
This predisposes the ventricles to enlarge under pressure. The enlargement of the ventricular volume is not accompanied by any significant change in the volume of the subarachnoid space. The subarachnoid space in obstructive hydrocephalus is reduced compared with normal subjects. Bech et al found no correlation between meningeal fibrosis and poor CSF outflow. No correlation was found between pathological changes in the parenchyma and the presence of B waves.