Wednesday, June 24, 2015

Brain Drain

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.