You're going to have an interview at some point before the surgery, probably by a nurse-practitioner, maybe in person, or it might be by phone. If it's anything like the five or six surgeries I've experienced, one of the questions will be "Do you wear a hair piece, wig, or any hidden appliances?" For crying out loud, answer truthfully. They've heard it all and seen it all, believe me, and it won't surprise them one bit. When you answer "yes", she'll advise you on how you should handle it-- whether it's OK to leave it in place, or if you should remove it before coming in.

These medical professionals (at least in the states) are bound by federal privacy laws known as HIPAA, and they're not going to blab. Their jobs depend on it. Why take the chance that you keeping a secret could jeopardize your surgery for any reason over something like this?

Relax, and focus your energies on getting over your surgery! Good luck.