Chicken arachnoid granulations: a new model for cerebrospinal fluid absorption in man.

Cerebrospinal fluid (CSF) absorption was investigated chicken and rat using infusion tests into the cisterna magna. Data were analysed according to a mathematical model by Johnson et al. Results in rat predicted a predominant lymphatic mechanism, which was confirmed by rapid outflow of X-ray contrast media into the olfactoric mucosa. In contrast, dynamics measurements suggested CSF drainage via arachnoid granulations in chicken. CSF spaces along the optic nerve were contrasted radiographically resulting in venous drainage. Electron microscopically, villus-like structures were found at the distal optic nerve connecting the subarachnoid space with accompanying veins, resembling human arachnoid granulations. We hypothesize that CSF absorption through arachnoid villi in microsmatic chicken reflects the situation in man very well.