What causes a neuroma?

I was told I may possibly have a neuroma in my elbow. I had surgery for ulnar nerve compression (elbow)this past autumn. Two months after surgery I was injured, elbow bore the brunt of it. No fractures.

I've experienced a lot of burning pain in the palm of my hand below little and ring fingers, pain has developed in elbow incision area.

I was told I may have a neuroma in my elbow and could have exploratory surgery to see if there is one in my elbow or anything else that could be causing pain. I had a nerve conduction test which came back as normal.

I was wondering what causes neuromas?