I had surgery on Monday, and I didn't intend on telling anyone I'd had ANYTHING done. I was able to leave the hospital on my own in a cab, but when I returned to the house of the two friends I was staying with, I wanted to explain why I was walking so slowly and asking them to reach up to high cupboards for me.
Years ago, on this site there was an explanation that I thought was the best if you do feel inclined to offer one. "Had a growth removed. Not malignant, thankfully. Thanks for your concern." While this explanation is obviously intentionally misleading, it is the truth so you'll never be caught in a lie as a result.
Ultimately this is what I told them. (I thought to say this because I'd read it somewhere else on the forums!) I said I'd had some growths / cists removed from my chest and couldn't move my arms too high because it could tear the stitches. None of this is far from the truth, and it didn't elicit any more questions.
Some other friends came over the next day. One of the people I'd already told jokingly made mention of how I was "walking like a penguin" because of my surgery. The other friends were shocked and asked what happened. I said I'd "had my soul removed" because I'm a journalism student, then the friends I'd told it was a growth laughed, and we all laughed because everyone knew it mustn't have been serious. They didn't ask me anything else, but if they ask the other two, they'll be told the exact same thing about the growth. Just make sure you don't tell different people different things; the story will become conflated and hard to manage, and everyone will know you're lying if one person repeats a different story to another.
Don't sweat it, people generally won't question much if you just say it's a benign growth or something. Those close to you will just want to know you're okay. As Paa_Paw said, you don't owe it to ANYONE to tell them anything. But if anyone presses you for more specifics, and you don't want to seem rude or abrupt, just say all you know is that it wasn't dangerous, but the doctors saw fit to take it out. Give a smile and say you'd prefer to forget about it. Laugh it off as insignificant.
BTW: Now back at home (with parents), five days post-op, and I haven't told them a thing. It's nearing winter now, so if they see my garment peeking through clothes I'll just say it's getting cold and it's a singlet. It
is getting cold. It
is (essentially) a singlet. No lies. Having an oddball like me as a son for 21 years, though, wearing something under my shirt is probably one of the less concerning things they've had to deal with, so I doubt it'll even come up.