Prenatal Ultrasound Abbreviation

I had my 19 week ultrasound today and the technician was not a talker. She labeled each still with an abbreviation (Lt. Hum = left humerous, 4 ch = 4 chambers, etc.) One of the many stills she saved she labeled “GV”. Any guesses as to what that might stand for?

Thanks!

A bit technical, but here you go:

Thank you for the link on vein of Galen, cher3. Both hubby and I could have sworn that still showed the legs and part of the torso, but it was really hard to make out.