Final answer:
External injuries without underlying injury are coded to the AIS region and assigned to the ISS region.
Step-by-step explanation:
When an external injury occurs without underlying injury, it is coded to the specific AIS (Abbreviated Injury Scale) region, but assigned to the ISS (Injury Severity Score) region. AIS is a system that categorizes injuries based on their anatomical location and severity, while ISS is a scoring system that quantifies the severity of multiple injuries sustained by an individual.