Objective: Normal-pressure hydrocephalus (NPH) is a potentially treatable syndrome with abnormal cerebrospinal fluid dynamics. Meningeal fibrosis and/or obliteration of the subarachnoid space has been suggested as the pathoanatomic basis. The purpose of the present study was to investigate whether meningeal fibrosis causes increased resistance to cerebrospinal fluid outflow (R(out)) and/or increased B-wave activity and whether pathological changes in the brain parenchyma after brain compliance, causing increased B-wave activity.
Methods: The study involved a group of 38 consecutively studied patients with clinical and radiological evidence of idiopathic NPH, for whom a frontal brain biopsy was obtained. For 29 patients, hydrodynamic criteria of NPH were fulfilled and a ventriculoperitoneal shunt was performed.
Results: Meningeal fibrosis was found in 12 of 25 biopsies containing arachnoid tissue, but no correlation with R(out) or B-waves was found. Pathological parenchymal changes, most often Alzheimer's disease (10 cases) or vascular changes (10 cases), were found in 21 biopsies, but no correlation with B-waves or R(out) was found.
Conclusion: The results suggest that leptomeningeal fibrosis is not the only pathoanatomic basis of increased R(out) and/or B-wave activity in patients with NPH and that various degenerative changes in the parenchyma may be responsible for the altered cerebrospinal fluid dynamics characteristic of NPH.