Here's one, from the faq:
Venous angioplasty is rarely used because the incidence of re-stenosis is so high. This is because narrowed veins are usually scarred, and the scar tissue is very elastic. So, if a narrowed vein is treated by balloon venoplasty, it is like stretching an elastic; remove the balloon from the vein and its elastic properties make it return to its original shape.
Here is a more trusted source, Dr. Sclafani, stating that the narrowings above the valve do not seem to him to be scar tissue:
just because you think that the narrowing is scar tissue, doesnt mean it is. In fact, i do not think it is when the narrowing is in the vicinity of the valves.
i was just making the statement that most IRs believe it is scar until proven otherwise and thus are over dilating.
I think it is not and have backed off on sizeing balloons to conform to the diameter of the vein to start.