The effect of increased CSF pressure on interstitial fluid flow during ventriculocisternal perfusion in the cat.

Transependymal absorption of cerebrospinal fluid (CSF) in hydrocephalus is suggested by periventricular edema, but the necessary bulk flow of interstitial fluid (ISF) has not been found. We performed ventriculocisternal perfusions in adult cats using CSF with the extracellular marker [3H]sucrose. CSF pressure was maintained at -5(control), 20 or 40 cm H2O for 2 or 4 h. Some animals had perfusions with isotope for the full experiment while others had an isotope-free perfusion for 2 h followed by a delayed-pulse with isotope. Apparent diffusion coefficients and distribution spaces for sucrose were determined from depth of isotope penetration. White matter apparent diffusion coefficients were statistically increased compared to controls for the 4-h 20 cm H2O and 2-h 40 cm H2O experiments. Apparent diffusion coefficients for delayed-pulse experiments at increased pressure were greater than those of full-pulse. Sucrose distribution spaces were not enlarged at the various pressures. Alteration of ISF transport in periventricular white matter occurred with increased pressure. These time-dependent changes in bulk flow rate indicate either a decrease in normal ISF flow toward the ventricle or reversal of transependymal ISF flow.