Arachnoid granules: Dandy was Dandy, Cushing and Weed were not.

Errors can be instructive. It seems that Harvey Cushing and Louis Weed provided the medical world with a faulty theory of cerebrospinal fluid absorption. Louis Weed, working in Harvey Cushing's laboratory, initially studied the movement of substances in the cerebrospinal fluid by using low-pressure studies. Results of the low-pressure studies were considered unsatisfactory and high pressure experiments were undertaken and these had results similar to earlier work done by others in human cadavers. High pressure results demonstrating movement of fluid through the arachnoid granules were deemed correct. Because of Cushing's position of authority, the theory became accepted as fact and in time proved to be entrenched dogma. Walter Dandy demonstrated in experiments on hydrocephalus and the surgical removal of the arachnoid granule system that the fluid was produced by the choroid plexuses and not absorbed by the arachnoid granules. His work was dismissed by Weed as unreliable. Examination of the pattern of deposition of corpora amylacea on the surface of the brain provides evidence that cerebrospinal fluid does not pass through arachnoid granules but passes through the choroid fissure and is recycled through choroid plexus portals. The choroid plexus portal theory can explain the findings in the low-pressure experiments of Weed. Bias and pride seem to be the source of the faulty theory. Entrenched dogma is resistant to challenge.