Paolo Zamboni (born 25 March 1957, Ferrara, Italy) is an Italian doctor who claims to have found in an unblinded preliminary study that in over 90% of the participants with multiple sclerosis there were problems in veins draining their brain, like stenosis or defective valves. He also noticed high level of accumulation of iron deposits in the brain, supposedly due to restricted outflow of blood.
According to Zamboni some symptoms of multiple sclerosis in his own wife as well as 73% of his patients abated after an endovascular procedure to open these veins.
The theory is controversial. The National Multiple Sclerosis Society has said that, while "there is not yet enough evidence to conclude that obstruction of veins causes MS," that "[Zamboni's] hypothesis on CCSVI and its corrective treatment is a path that must be more fully explored and one that we are supporting with research funding." Since 2010, there has been more research that disputes the Zamboni theory. According to a recent research carried out at the Cardiovascular Diseases Section, Department of Emergency and Organ Transplantation (DETO), University of Bari (Italy), venous echo-color-Doppler (ECD) showed that chronic cerebrospinal venous insufficiency (CCSVI) syndrome is related to multiple sclerosis (MS). 
^Traboulsee, Anthony L., et al. (2013, October 9). Prevalence of extracranial venous narrowing on catheter venography in people with multiple sclerosis, their siblings, and unrelated healthy controls: a blinded, case-control study. The Lancet. Retrieved from http://press.thelancet.com/CCSVIcathetervenography.pdf
^Ciccone M.M., et al. Multigate quality Doppler profiles and morphological/hemodynamic alterations in multiple sclerosis patients. Curr. Neurovasc. Res.. 2012 May;9(2):120-7. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/22475396