Jugular reflux mimicking dural arteriovenous fistula

This is a good example of retrograde venous flow mimicking arteriovenous shunting. If this was forward (downward) arterialized flow it would be expected to be saturated out in the lower slabs. 

To confirm this a time-resolved MR angiogram or CTA (provided contrast was injected on the right) or catheter angiogram could be performed. 

ApparentlyHigh signal, suggestive of arterialised flow, is seen fromin the left internal carotid artery via the inferolateral trunk tocavernous sinus and down the inferior petrosal sinus, into the jugular foramen with additional high signal suggesting retrograde flow up the sigmoid and transverse sinus. This suggests

These findings could be (and were) interpreted as being from a dural arteriovenous fistula from the inferolateral trunk arising from the internal carotid artery.

In fact it is, these findings are due to retrograde flow up the left internal jugular vein (reflux) ¹. 

A few clues indicate that this is the case, in addition to it being increasingly recognised as a normal finding. Firstly the left internal jugular is the most likely location due to the presence of venous valves in the neck and the non-dominant size of the vein. Secondly, if this was forward (downward) arterialized flow it would be expected to be saturated out in the lower slabs, whereas instead, the brightest signal is in the lowest parts of the visualised internal jugular vein. Otherwise, MR angiography is unremarkable other than a calcified atherosclerotic change, particularly prominent in the dominant left vertebral artery, better seen on CT (not shown)