I was wondering if you could elaborate on that a little more. Are the stenoses a defect in the structure of the vein, where it "funnels down" or narrows at one point? Or is it the buildup of tissue on the inside of the vein wall? Or something else?
Firstly, not all resistance to flow is caused by stenosis (narrowing).
Narrowing can be secondary to
1.hyppplasia,or failure to grow to proper sized
2. extrinsic compression by a duplicated vein
3.transverse webs of tissue acting like a lid on the vein
4. or septum that divides the tube (jugular) into two smaller tubes
5. A diverticulum that compresses the vein
6. by valves that are stiff and do not open and close properly
7 valves made of several leaflets that end up fused together
8 valves that are located in abnormal locations
Almost all of these narrowings occur near the confluens of the jugular vein with the subcclavian where valves are seen normally in about 85 per cent of patients. Problem is these valves are highly dysfunctionally developed in patients with MS. I think the IVUS really shows this really well.The venogram shows narrowing but the IVUS shows that the narrowing is valvular.
These narrowings are not inflammatory strictures and they are not "buildup of tissue on the wall of the vein (sort of like plaqeu).
My guess is that this is maldevelopment of the valves in the fetus.
There are other malformations of veins that are well known. They include problems with the veins of the liver as they join the inferior vena cava. This well known entity is called Budd Chiari syndrome and results in major problems of the liver.