The hidden devil: unexpected retained knife in the chest wall.

We report a 52-year-old woman presenting with stab wounds on her back and upper extremities. A knife retained in her chest wall was not discovered in the emergency department. This case reminds us that an obvious foreign body can be missed even after obtaining a detailed history, complete physical examination and plain film. Particularly, a retained foreign body increases the risk of infection and may cause further internal organ injury. We suggest that patients undergo computed tomography (CT) scanning whenever a penetrating wound cannot be explored adequately or the trauma surgeons are unable to perform detailed examinations on the injured patients. The CT images could delineate the course and severity of the penetrating injury, and decrease the risk of a retained foreign body.