Cerebrospinal fluid and extracellular fluid: their relationship to pressure and duration of canine hydrocephalus.

Fifteen greyhound dogs were made hydrocephalic by the transsphenoidal injection of silicone into the basal cisterns at the level of the tentorial incisura. Six of these animals had ventriculocisternal perfusions 4 weeks later and six at 8 weeks, half at 150 and half at 100 mm H2O. Three 12-week dogs were perfused at 150 mm H2O. Serial sections of brain from the ependyma of the left frontal horn to the overlying pia were counted for 14C inulin and 3H methotrexate uptake. Tissue concentrations of both markers varied indirectly with distance from ependyma and from pia, and varied directly with perfusion pressure. The data indicate that the diffusional pathway between cerebrospinal fluid (CSF) and extracellular fluid (ECF) can be modified by CSF pressure changes, i.e., CSF flows from the ventricles and subarachnoid space into the extracellular space when CSF pressures are raised. Brain uptake of inulin and methotrexate was significantly increased in the dogs made hydrocephalic 4 weeks prior to perfusion, but was less so in the 8-week hydrocephalics. Uptake of the tracers in three 12-week animals was similar to that found previously in normal dogs at elevated pressures. These findings correspond in location and time to the periventricular lucencies that are seen by computed tomography in human subacute hydrocephalus. They are apparently due to pressure-related changes in the volume of the ECF.