A: All penetrating injuries that do not involve underlying structures are assigned to the External body region when calculating an ISS with the exception of penetrating injuries to the head and massive penetrating injuries to the face. The AIS 2005 dictionary spells this rule out more clearly than previous editions. Remember, when coding penetrating injuries, always code the underlying injuries if known, and when they are known, the skin injury is considered to be included in that code and is not coded separately.