I once had to take a day off for an abortion. I said I was getting minor surgery, and my boss assumed I was having dental work done. When I came back the following week, she asked me about my extraction or something...I can't remember exactly how she phrased it, but I wasn't very good at thinking on my feet, so I was startled. I said I had had a growth removed, which was absolutely true. I should think that the same explanation (times two) would work for top surgery. After all, you weren't born with the things; they grew!
I did have a nosy coworker who just had to know WHERE the growth was. I was again caught off guard and stammered something. Nowadays, I would make some rude remark.