Daniel S. Reich, NINDS.
The lymphatic system is part of your body’s waste disposal system. Lymphatic vessels slurp up excess fluid and proteins from tissues and shuttle it through small structures called lymph nodes. Immune cells in the nodes can detect invading pathogens and launch an immune response.
For years, scientists thought the brain lacked this kind of waste removal system. But in 2017, researchers found evidence of the lymphatic system in the brain using MRI scans and a dye that could pass through the tightly guarded blood-brain barrier. The images they got, like the one above, not only highlighted the blood vessels they expected to see, but also other vessels they suspected were part of the lymphatic system, stained in purple. (The dye also incidentally highlights the choroid plexus, the curved structure in the middle of the brain that produces cerebrospinal fluid.) The discovery could reorient how scientists view the relationship between the brain and the immune system and help answer a question that has stymied researchers for decades.