To what extent has the pathophysiology of normal-pressure hydrocephalus been clarified?

The causes and pathophysiology of idiopathic normal-pressure hydrocephalus (NPH) still remain poorly understood. We reviewed the recent pertinent literature on NPH from the past 3 years (1994- 1996) in this journal [Crit Rev Neurosurg (1997) 7:263-275] and here review further manuscripts that appeared mainly in 1997. Recent investigations suggest that idiopathic NPH may be a primary cerebral parenchymal disease rather than a disorder of cerebrospinal fluid (CSF) absorption. The pathophysiology of idiopathic NPH has a wide spectrum ranging from purely hydrodynamic problems owing to a CSF absorption defect to parenchymal changes caused by hemodynamic problems owing to ischemic vascular risk factors. Magnetic resonance imaging (MRI) of NPH frequently shows ischemic vas-cular encephalopathy. NPH may coexist with subcortical white matter vascular encephalopathy, because Binswanger's encephalopathy and idiopathic NPH share common clinical symptoms. Most patients with suspected NPH may suffer from both problems. Because of MRI findings of suspected NPH, ischemic parenchymal changes caused by vasculopathy have been receiving attention. Brain biopsy findings of suspected NPH suggest the presence of parenchymal changes caused by vasculopathy such as arteriosclerosis. Patients with brain biopsy findings of Alzheimer's disease may benefit from shunting. Pathological changes seen by brain biopsy are not specific for NPH. The information accumulated so far about NPH shows a wide clinical spectrum and multifactorial etiology. Therefore, patients with NPH are inhomogeneous, and this makes it difficult to diagnose and select patients for shunting.