The puzzle of where cerebrospinal fluid is absorbed: new pieces.

The widely held theory of cerebrospinal fluid (CSF) absorption by the arachnoid villus system cannot explain the movement of substances within the fluid, the deposition pattern of corpora amylacea on the surface of the brain, and pathological findings in neurological disorders. Experiments studying the movement of melatonin and inulin in the CSF compartment demonstrate that some CSF recycles into the ventricular system and CSF contacting tissue diffusely absorbs some. Photomicrographs of a suprapineal recess portal into the third ventricle are presented. A cycling theory of CSF assigns function to the structure of the choroid fissures and the suprapineal recess.