The prelymphatic pathways of the brain as revealed by cervical lymphatic obstruction and the passage of particles.

Light and electron microscopy was used to examine portions of the brain, the circle of Willis, and the internal carotid arteries of normal cats and rabbits, of sham-operated ones, and of those whose cervical lymphatics had been ligated. Carbon was injected into the cerebral cortex of some lymphoedematous animals. It was found that lymphatic ligation produced oedema of the brain, and a dilatation of the prelymphatic spaces around the vessels. Carbon was traced in these from the injection site, around the minor and major vessels, in the adventitia of the internal carotid artery, entering lymphatics adjacent to it, and finally in the draining lymph nodes. The oedema and dilated spaces were not present in the control animals. This was taken to indicate that there is a continuous system of non-endothelialized spaces and potential spaces-the prelymphatics-draining the brain into the cervical lymphatics. The protein in these spaces appeared to be increased if the lymph-oedema had lasted three weeks as compared to 24 hours, indicating that one of the major roles of this system is the removal of protein.