2015 is a watershed year for our understanding of brain
drainage. A lymphatic system for the
central nervous system has been discovered.
For two centuries it was thought none existed, its absence the second pillar
of the blood-brain barrier. Now, a
full-fledged lymphatic network it has been identified microscopically, hidden
in the walls of the dural meninges of the venous sinuses that drain blood from
the brain into the internal jugular veins.
The research also demonstrated the transport through these lymphatic
vessels of white cells, including T-cells, and CSF immune macromolecules. In 2015 another brain drainage system was
also discovered. Coined the glymph
system it permits the drainage of the interstitial fluid that surrounds brain
cells to flow out between the astrocyte foot pads surrounding CNS capillaries
and venules.
Neuro-immunology will change, having failed for half a
century to document auto-immunity or in fact any direct attack by the immune
system on healthy myelin. The discovery
of a brain lymphatic drainage system opens a new front on the advances in
understanding brain perfusion and venous drainage. Do these newly discovered systems function
normally in multiple sclerosis?
Few internal jugular venoplasties are performed for MS
currently, primarily because of the high re-stenosis rate, 30-50% of patients
have a return of their pre-venoplasty symptoms and ultrasound shows the vein
obstructed again. We are waiting for
better methods to keep the veins open.
But why venoplasty helps so many patients is still an open
question. Does the discovery of the
brain’s lymphatic system, which drains into the internal jugular veins, provide
us clues? Previously it was theorized
that venous hypertension resulted from the jugular narrowing, or that sluggish
flow in the venules allowed red cells and iron to cross the blood-brain barrier
inciting inflammation. Now we can ask if
Paolo Zamboni’s theory of chronic cerebrospinal venous insufficiency is
associated with a lymphatic insufficiency as well. We can expect soon to know what cells and
proteins are passing through these lymphatics and how they affect the
oligodendrocytes that make myelin, and how lymphatic flow relates to venous
flow.
