Those with a deformity on your genitals, when do you tell a potential partner or hookup about it?

I have a small cist on my testicles. Had an ultrasound and it's confirmed harmless, but it makes me insecure.

Developed it a few years ago. Haven't hooked up with a woman since getting it. I plan to resume dating after I get my vasectomy/confirm being sterile. (Don't want to risk having kids at all.)

Obviously you should tell them prior to sex, but when?

Yes, I'm embarrassed to be asking at 27 years old.