===Fibrin sheath===
In a normal case, the contrast flows straight out from the catheter.<ref name=Helsingborg/> Contrast flowing at a skewed angle compared to the catheter means is regarded to be a suspected fibrin sheath.<ref name=Helsingborg/>
A definite fibrin sheath is visualized as contrast flowing backwards around the catheter, looking like a thickening of the distal part, before exiting at a more proximal part of the catheter.