In healthy humans, the cerebrospinal fluid (CSF) is renewed approximately four times per day, and the skull is lined with membranes that protect the brain and spinal cord. More than 200 years ago, it was speculated that the brain was also protected by lymphatic vessels whose purpose is, among other things, to transport bacteria and debris to the lymph nodes to be destroyed and eliminated from the body. In 2018, the hypothesis of the existence of lymphatic vessels in the brain was confirmed using state-of-the-art imaging technology.

In aging adults, impaired function of lymphatic vessels can lead to accelerated accumulation of toxic amyloid beta in the brain. The traditional model for how the CSF drained was directly challenged when the scientists injected molecular tracers into the CSF and demonstrated that the drainage occurred through the lymphatic vessels—demonstrating a new route for clearing molecules from the brain. The presence of a “brain drain” is now understood to be critical for maintaining intracranial pressure and removing waste.

Jony Kipnis, Ph.D., University of Virginia School of Medicine