Hi: I'm not a dr either but have had both of these and anteriolisthesis is when the vetrebra slips forward (towards the abdomen) and retro... is when it slips in the opposite direction.
Hopefully your surgeon will be able to do something for this, if you *need* it. Sometimes they leave these alone until there is some degree of nerve involvement (pain, compression). Does it say what the degree of slip is, like numbers 1-4?
Good luck, and I'm sure they will be able to figure something out for this.