Couple of points:
1) Please see Rici's video. This is a real time unpolluted picture. It clearly shows blood flowing back as it tries to get past the narrowed vein and cannot. Due to pressure, it refluxes back.
2) The inflammation sites at mainly around the veins. So the iron must be depositing at that place.
AD1) I saw Rici's video. It doesn't prove you statement that blood is flowing back. All you can see is the moment when contrast solution is injected upstream and quickly and freely flow downstream the vein.
This so-colled reflux theory in vains is unexplaineble according to hemodynamics and hydraulic/phisic laws. Local turbulence is possible in places where cross section of the vain is changing, but global flow is allways downstream the presure line.
AD2) Even if this is true (The inflammation sites at mainly around the veins) iron deposits certainly can not be due to a possible narrowing of the veins in the neck. Osmosis and blood brain barier is something different issue and have not connection with blood flow dynamic in large veins.
There is an X volume of blood being pumped out of heart. It needs to go through complex processing before it gets back to heart. Assume there is a choke point which impedes all the blood flow, what would happen?
Pressure would be created. This pressure has to be absorbed somewhere.
It cannot be absorbed in veins unless there is a puncture. So probably it gets settled around the veins.
I did not understand what you mean by, "can not be due to a possible narrowing of the veins in the neck". Because these are dead cells that are probably getting accumulated as they have nowhere else to go. This part has nothing to do with BBB. BBB comes into picture only when you have enough dead cell accumulation, the immune system starts the process of cleaning them up and in the process kills healthy brain and myelin (??) also ...