http://link.springer.com/article/10.100 ... 016-4314-6
and a quote from each:
Both observers found stenosis in the IJVs with fair agreement. Most stenoses were located in the upper IJV segments.
It's known that those upper jugular narrowings can be physiological narrowings, that are present in some positions but not present in others, because of skull base or muscular compression of the vein that is relieved when the neck is turned a different way.Areas of narrowing greater than 50% occur most commonly in the upper cervical and skull base regions.
These physiological stenoses are distinctly different than stenoses that occur within the vein, such as a valve or septum that blocks the flow intraluminally regardless of how the head is turned.
I think these researchers who are drawing the conclusion that people without MS have stenoses too and therefore that weighs against the CCSVI hypothesis need to have a way to disclude physiological stenoses. Looking specifically at the area of the valves and not the length of the whole vein might be enough to achieve this. If in people without MS, these stenoses tend to be at the top of the vein near the skull base, then that needs to be compared to the location of the stenoses in people with MS. If our stenoses are not like those of the people without MS, i.e. ours are throughout the vein or likely to be in the valve are of the vein, then that help separate out what is different about us and it would support the CCSVI hypothesis.