The pathogenesis of normal pressure hydrocephalus: A theoretical analysis |
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Authors: | David N Levine |
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Institution: | (1) Department of Neurology, New York University Medical Center, New York, USA;(2) RIRM 311, 400 E. 34th St., NYC, NY 10016, USA |
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Abstract: | Hydrocephalus is an abnormal accumulation of cerebrospinal fluid (CSF) in the cerebral ventricles, usually caused by impaired
absorption of the fluid into the bloodstream. Despite obstructed absorption and continued secretion of CSF into the ventricles
at a near normal rate, the ventricular CSF pressure (VCSFP) is often normal. We attempt to understand how hydrocephalus can
exist with normal VCSFP by exploring the role of the brain parenchyma in absorbing CSF in hydrocephalus. We test three theories:
(1) the ventricular wall is impermeable to CSF; (2) ventricular CSF seeps into the parenchyma, from which it is efficiently
absorbed; and (3) ventricular CSF seeps into the parenchyma but is absorbed inefficiently.
We model the brain as a thick spherical shell consisting of a porous, elastic, solid matrix, containing interstitial fluid
and blood. We modify the equations of poroelasticity, which describe flow of fluid through porous solids, to allow for parenchymal
absorption. For each of the three theories we calculate the steady state changes in VCSFP and in parenchymal fluid pressure
caused by an incremental defect in CSF absorption. We also calculate the steady state changes in fluid content, tissue volume,
tissue displacement, and stresses caused by a small increment of VCSFP. We conclude that only the second theory—seepage of
CSF with efficient parenchymal absorption—accounts for the clinical features of normal pressure hydrocephalus. These features
include sustained ventricular dilatation despite normal VCSFP, increased periventricular fluid content, and localized periventricular
white matter damage. |
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