The normal crease at the bottom of the butt is known as the infra gluteal fold. This fold is very often duplicated or triplicated with weaker but prevalent folds going down onto the posterior thigh. If the second fold is on the back of the thigh and has fat in between the first and second folds, we refer to this fat filled area below the buttocks as the "banana". I and several other authors have written papers on this particular phenomenon.This fat, whether it is connected to the bottom of the buttocks or else even on the upper posterior thigh, can be suctioned out leaving one with a single crease on the buttocks. Liposuction of this area is tricky to say the least. These folds keep the buttocks intact and, if the primary fold is injured, it can lead to distal migration of the infra gluteal fold, i.e. your butt can drop.Diagnosing your particular congenital anomaly requires an experienced plastic surgeon who has dealt with liposuction of the banana in the past and who understands the dynamics of this particular portion of the body. To find a good Board Certified plastic surgeon in your region, I suggest visiting the American Society for Aesthetic Plastic Surgery website to find surgeons in your area, then look them up on RealSelf, Health Grades, Vitals, etc. to see what other patients have said about them. At that point, I would seek consultation with two or three of these experienced surgeons and see what they say after an in person, physical examination.