Cranial trauma is a term used for when a person is hit on the head violently or suffers from an injury from hitting their head.
In 2369, Dr. Julian Bashir examined Chief Miles O'Brien after he had been found to be suffering from aphasia. Bashir could not find any signs of cranial trauma on O'Brien head, which was usually associated with aphasia. It was later discovered that O'Brien had contracted aphasia from an aphasia device planted on the station in 2351 by Bajorans when it was under Cardassian rule. (DS9: "Babel")