What Causes Painless Lump Behind The Ear?

Good evening. About ten years ago I had gone in for a dr visit and had them check out a lump on my hairline about an inch and a half behind my ear lobe but not in the middle of my neck. It was hard and did not move. No biopsy was done, never really bothered me. Doesn t nevessarily bother me physically as much as it worries me. I intend to get it checked out, but any thoughts or input are welcome in regards to causes, what it could be and what type of action I should take? Thanks in advance!