Cystic vein

The cystic veins (usually multiple small veins rather than a single cystic vein) drain venous blood from the gallbladder   and the cystic duct. The cystic veins either drain into various branches (within the liver) and tributaries (outside the liver) of the hepatic portal vein.

Cystic veins do not accompany the cystic artery. 

Anatomy
Those cystic veins that arise upon the superior aspect of the body and neck of the gallbladder pass within loose connective tissue that occurs between the gallbladder and liver; they then enter the liver to drain into branches of the hepatic portal vein within the liver.  

The rest of the gallbladder drains into 1-2 small cystic veins which then usually empty into either the hepatic portal vein within the liver, or into tributaries of the hepatic portal venous system that drain either the proximal bile duct or hepatic ducts; rarely, one or more cystic vein(s) drain(s) into the right branch of the hepatic portal vein directly.