Much like how buildings drain excess fluids through pipes that lead into a sewage system, human bodies also have a network of vessels for moving things around. It’s called the lymphatic system, and while this network seems to run all throughout the body, it has only recently been observed around much of human brains. Using magnetic resonance imaging (MRI) clinicians injected a dye-like substance to help them visualize the pooling of liquid in human and marmoset brains. In MRIs of both species, researchers saw evidence that fluid leaked out of the blood vessels surrounding the brain and collected into what seemed to be lymphatic vessels contained in the brain’s dura.
This newly identified path of waste is potentially relevant to degenerative diseases related to aging such as Alzheimer’s disease, where toxic by-products build up in the brain instead of getting removed. Another potential avenue of research is the way the lymphatic system helps traffic immune cells between the blood and different tissues. Blood vessels directly supplying blood to the brain have a protective layer called the blood brain barrier that controls what gets in, but the arteries and lymphatic vessels outside the brain don’t have the same gating system. This means that they are an easier entry point for dysfunctional immune cells. With the new discovery of lymphatic vessels present in the dura collecting and draining fluids, future studies will focus on whether immune cells can also travel to and from the brain via these vessels.