The central nervous system is devoid of conventional lymphatic vessels, unlike other organs containing networks of lymphatic vessels, which process various substances, such as wastes, fluid, proteins, and cells from tissues to lymph nodes. However, the lymphatic perivascular drainage system in the brain performs the main function assigned to systemic lymphatic vessels. Analysis of the lymphatic perivascular drainage system dates back as far as the nineteenth century, where it was shown that Indian ink injected into cisterna magna drained to the cervical lymph nodes (Schwalbe, 1869; Weller et al., 2010).
