A proposed model of cerebrospinal fluid circulation: observations with radionuclide cisternography.

PURPOSE: To determine the mechanisms of the tracer distribution at radionuclide cisternography (RC). METHODS: Ten patients with venous vasculitis were studied with RC. Flow phantom studies were performed mimicking cerebrospinal fluid (CSF) circulation with and without a main outlet comparable to the pacchionian granulations. RESULTS: Nine of the 10 patients had normal findings on RC images, including a maximum uptake over the vertex at 24 hours. In all patients, a second maximum occurred in the lumbosacral area. The flow phantom studies showed no tracer accumulation at an open outlet corresponding to the pacchionian granulations. On the contrary, a maximum arose without such an outlet. A maximum always arose at the closed dead ends of the phantom, including the lumbosacral area. CONCLUSION: The commonly accepted flow model for CSF circulation needs to be revised. The pattern of the normal RC cannot be explained by a bulk flow transport of the tracer to an outlet at the pacchionian granulations but rather by a primary mixing caused by pulsatile flow with a secondary dilution by newly formed CSF from the ventricular system. We suggest that the main absorption of the CSF is through the central nervous system to the blood.