Explanation of metrizamide brain penetration: a review.

The penetration of intrathecally injected metrizamide into brain and spinal cord substance is a phenomenon that has surprised and puzzled radiologists. No suitable explanation has been offered in the radiologic literature. This article reviews the recent literature on the relationship between the cerebrospinal fluid (CSF) space and the extracellular fluid (ECF) space of the brain. Recent evidence has shown that these spaces are in fact one compartment with no diffusion barrier between them. Thus, penetration of metrizamide into the brain is an expected rather than surprising phenomenon. An explanation is offered as to why metrizamide does not penetrate edematous or infarcted portions of brain on the basis of a pressure gradient between damaged brain ECF and CSF spaces.