Ask Dr. Z

This is a 21-day-old patient with a complex intrahepatic arterioportal fistula. The report says to apply modifier -63, which I have never used before but seems to apply. They are embolizing two arterial feeders to this AVM via an umbilical venous approach. Sounds like they went through the ductus venosus and selected both arterial feeders separately (which appear to stem from bilateral inferior phrenic arteries). My question on the catheterization is would this be two second order venous catheterizations 36012 x 2, or does it switch to arterial? If we code arterial, what order of selectivity? They're trying to assign 36247 and 36248. Also, would this be coded 37241 for venous embolization or 37242 for arterial? What would be the correct cod, and should I use a -63 modifier?