CCSVI (chronic cerebrospinal venous insufficiency) is thought to be a vascular condition in which an obstructed flow of blood from the brain and spinal cord back to the heart may cause damage to the nervous system and lead to MS.
Professor Paolo Zamboni, a vascular surgeon from the University of Ferrara, Italy, first observed and named CCSVI. His 2008 paper suggested that reflux pressure in the cerebral veins might induce leakage of blood around the small veins in the brain, and subsequently inflammation which causes MS and other diseases.
Multiple publications on CCSVI have appeared since then, and Zamboni has continued his own research, but the findings remain inconclusive. Studies are ongoing, but for now, the evidence that CCSVI causes MS is not strong.