What causes the venous stenoses and abnormalities leading to CCSVI?

At present, no one is certain. Dr. Zamboni and others have theorized that many, though not all, of the stenoses are congenital. Support for this assertion comes from the fact that some types of venous obstructions, particularly certain cases of hypoplasia, atresia, and agenesis, are such profound abnormalities that they appear to be congenital  or developmental malformations. However, the etiology of the many other types of stenoses, blockages, and other venous malformations causing CCSVI is largely unexplored, and requires more research.