Unusual reflux of contrast into the azygos system, highlighting its anatomy on the CTPA study. 

This case has a common configuration of a common trunk of the hemiazygos and accessory hemiazygos draining into the azygos vein. It also demonstrates the extensive communication with the vertebral venous plexus as well as the communication between the accessory hemiazygos and the left superior intercostal vein (which is more common than no communication).