Until recently, it was thought the brain had no lymphatic vessels. Research in 2012 proved otherwise.
Lymphatics of the Brain
In this study, scientists injected tracer dye into the subarachnoid space of the brains of living mice.
Subarachnoid space showing CSF. Cerebral spinal fluid travels around the brain & spinal cord & in the ventricles of the brain providing nutrients & removing waste.3
The subarachnoid space is found within the membranes (called meninges) that cover the brain & spinal cord.
Meninges
There are three layers of protective meninges. The inner layer is called the pia mater. Between the inner layer & the middle layer (called the arachnoid meningeal layer) is the subarachnoid space that houses the cerebral spinal fluid (& blood vessels). The outside layer of meninges is called the dura mater.
Cervical lymph nodes & CSF
Researchers followed the dye they had injected during their study. They observed that CSF drained from the inner brain (the CNS or central nervous system) to lymphatic vessels in the outer brain (the dura mater meningeal layer) before draining to the cervical lymph nodes in the neck.4 So, this study showed lymphatic vessels were present in the brain – the outer dura mater meningeal layer in mice.1,2 (Turns out, they’re in humans, too, as well as the spinal cord meninges.)4
Perivascular channels
The pia mater meningeal layer contains spaces known as perivascular channels (also called “Virchow-Robin” channels). These channels are created by the space between blood vessel walls & the inner pia mater meningeal layer. Cerebral spinal fluid (CSF) mixes with interstitial fluid (fluid found within the tissue space between cells – the fluid we deal with in lymphedema) continuously within this perivascular space before draining to the lymphatic vessels in the outer dura mater.
Where does dementia come into the picture? Find out next time as we continue to part 2.
References
1 https://www.nih.gov/news-events/nih-research-matters/new-brain-cleaning-system-discovered
2 https://www.nih.gov/news-events/nih-research-matters/lymphatic-vessels-discovered-central-nervous-system#:~:text=The%20lymphatic%20system%20carries%20white,was%20termed%20the%20glymphatic%20system.
3 https://www.nih.gov/news-events/nih-research-matters/new-brain-cleaning-system-discovered
4 Hershenhouse KS, Shauly O, Gould DJ, Patel KM. Meningeal Lymphatics: A Review and Future Directions From a Clinical Perspective. Neurosci Insights. 2019;14:1179069519889027. Published 2019 Dec 31. doi:10.1177/1179069519889027 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7176397/#:~:text=They%20demonstrated%20lateral%20branches%20associated%20with%20spinal%20nerves%20and%20blood%20vessels.&text=The%20localization%20of%20the%20lymphatics,nonhuman%20primate%2C%20and%20human%20specimens.&text=Further%20anatomical%20evidence%20for%20this,meningeal%20arteries%20and%20venous%20sinuses.&text=However%2C%20this%20localization%20remains%20an,access%20from%20the%20dura%20mater
