After Dexter Morgan discovers that Ron Galuzzo is a cannibal, he realizes that Ron is clearly not The Brain Surgeon. Dr. Evelyn Vogel then suggests that he look into Arnold Gordon. She says Arnold resented her for calling him a psychopath and threatened to hurt her if she ever told anyone that he was one. Also, being a surgeon, he has the skill set to remove brain sections.
This clearly proves to be a dead end, since Arnold is never mentioned again.