CSF dynamics in hydrocephalus--with special attention to external hydrocephalus.

Cerebrospinal fluid (CSF) physiology, and the pathophysiology of hydrocephalus is briefly reviewed, with emphasis on the arachnoid villae and the CSF-venous interface. Five cases of benign "external hydrocephalus" are recorded and the literature of similar cases is reviewed. It is proposed that anatomical or functional obstruction of various etiologies at the level of the arachnoid villae accounts for the dilated subarachnoid pathways in these patients.