A 32-year-old multiparous woman undergoes vacuum-assisted delivery for arrest of descent at +1 station. After two pulls, the cup detaches from the fetal head. The obstetrician attempts reinsertion and achieves delivery after three more pulls. The neonate is born with a cephalohematoma and poor Apgar score (3 at 1 minute). Which investigation is most appropriate to evaluate for potential intracranial injury?