He is a patient of Dr. Evelyn Vogel, who was a trauma surgeon.
Arnold resented Dr. Evelyn Vogel for constantly calling him a psychopath and threatened to hurt her if she ever told anyone that he was one. After Dexter discovers that Ron Galuzzo is a cannibal, he realizes that Ron is clearly not The Brain Surgeon. Vogel then suggests that he look into Gordon. This clearly proves to be a dead end, since Gordon is never mentioned again.