CTA: What is this vein?

[KoolDude]

@Rather_b_hiking That is a collateral vein (Posterior Condylar Vein connects to Vertebral Venous Plexus and drains all the way down to Brachiocephalic vein/Subclavian Vein). Sometimes it is called deep cervical vein and it is an alternate route to drain the brain when your jugular veins are impaired. It is dilated because blood is rerouted to it since the right Jugular vein is compressed - tale-tale sign of IJVS. I captured some diagrams and explanations on the link below if you need more details on it.

CT Scan Pics, broken styloid or scan error? Compression?

@blistle Well, based on your symptoms and limited imaging you provided, I can safely assume, you are suffering from Internal Jugular Vein Stenosis (IJVS) symptoms. This, I think is due to compression of the Styloid fragment on your right IJV and since your left IJV is small and is also compressed by the C1, it can’t compensate it. I think your symptoms are so similar to mine (see here Visual snow and floaters - #4 by KoolDude), no surprises there because your IJVs are like mine, just the opposit…