Answer: You should report the procedure using a code from the 57000 series. Depending on the exact nature of the surgery, you could use 57000 (Colpotomy; with exploration) if the ob-gyn makes an incision in the vagina. Or you could use 57135 (Excision of vaginal cyst or tumor) if the physician cut out part or the entire cyst and didn't just incise it.
A Gartner duct cyst is a lateral vaginal wall congenital cyst leftover when the male tubules of the sexless fetus dissolve because the female tubules are taking over during fetal development. These cysts are also known as Wolffian duct remnants and are caused by the same thing as morgagnian cysts usually found by the fallopian tubes.