I'm running into a similar problem with some of the pre-med students that I am advising. The problem is that they don't know exactly what they want to do, and have made or are currently making choices that will effectively close the door on some, but not all, of their opportunities in the future.
With a D.O. and applying for allopathic residencies in neurosurgery is going to put you at a major disadvantage to the M.D. candidates. I didn't create that reality, but it's the truth. I have many colleagues who did osteopathic school and they are wonderful physicians, but I have not met nor have I heard of any osteopathic docs in an allopathic neurosurgery program. Furthermore, I don't think the American Board of Neurological Surgeons recognizes ANY osteopathic neurosurgery residency programs.
Unfortunately, as far as neurosurgery allopathic residencies are concerned, you shot yourself in the foot by going to osteopathic school. Why a D.O. instead of M.D.? That's the answer that all allopathic residencies will want to know. And unfortunately, they all already have a preconceived answer in their minds.