I have always had this large quarter sized bump behind my right ear. Ever since I can remember it's been there, it only hurts when I wear sunglasses or reading glasses. When I was 16 I finally had it removed, and I have yet to figure out exactly what it is.
I went through CTs, MRIs, x-rays, a whole battery of tests and went to every local ear nose and throat doctor. What they finally "diagnosed" it as was a mastoid austioma. It turns out it's just bone.
However...it grew back! It's been 10 years and it's the size the old one was before I had it removed.