I've not had any problems at airports with either the full body scanner I was worried I would but no one batted an eyelash!
Just prior to a pat down I've said I have an ostomy bag on my right side you will feel that. Some have made an effort to avoid it, ( maybe they were afriad of touching it) I always make sure it's emptied before clearing security.
I have travelled with a letter from my Doctor never had to produce it. Better safe than sorry.
I find with airport security people the more upfront and honest you are the better it goes. I've never been asked to step aside or go to a private room, if I was I would be nervous but keep in mind they are doing thier job they don't know me I dont' know them I may not be Angelina Joli but in that case when it comes to getting checked out at the airport I am one in a million!