Cincinnati Children's is a great hospital for kids. At 18, your brother may be at an age that might make it better to look at adult facilities to seek treatment. If your are wanting an adult provider, the Cleveland Clinic would be an excellent choice.
CCHMC is a great place to start. If you are not local, I would try to work with your family doctor for a recommendation. If that isn't possible, you can always go to cincinnatichildrens.org and find the number for the department best able to help you. The hospital has a Ronald McDonald House very close for out-of-town visitors, so you might be able to stay there when you come.
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