Retained foreign bodies are associated with up to 1.9% of all wounds.1 The presence of a foreign body in a wound increases the incidence of a wound infection.2 Retained foreign bodies are also a major cause of litigation against Emergency Physicians.3,4 A high index of suspicion for a retained foreign body must be maintained whenever there is the potential for a foreign body in a wound.5,6 This chapter focuses on ultrasound-guided identification and removal of subcutaneous foreign bodies.
Foreign bodies may be small, leave no skin entry marks, and consist of many different types of material. Almost any object (solid, liquid, or gas) can become a foreign body and present itself in a location where it should not reside. Standard radiographs and fluoroscopy are good at identifying radiopaque objects such as metal, gravel, and glass.7–13 The ability of these techniques to identify a foreign body varies by the size and composition of the foreign body.9 MRI and CT are useful to detect foreign bodies.12,14,15 These are expensive imaging modalities and the images vary depending upon the length of time the foreign body has been present.15 Certain foreign bodies may produce artifacts that diminish the MRI and CT image qualities.12 Plastic, hair, vegetative material, and rubber are not radiopaque and are not routinely identified on radiographs.6–8,10–13,16–18 Ultrasound (US) is able to identify radiopaque foreign bodies. US can also detect foreign bodies that are not radiopaque due to their different echotextures in relation to surrounding structures.6,8,14–30
Foreign bodies can be present in almost any part of the body. Foreign bodies can be detected with US even when they are found in nontraditional places. They have been identified in the eye,31 esophagus,29 and tongue32 with US. Foreign bodies isolated to small spaces, such as in the web spaces of the hand, may not be identified due to the size of the US probe footprint and the difficult anatomic location to scan.26
Not diagnosing foreign bodies can be dangerous for the patient and lead to an increased risk of complications. Legislation to introduce an aluminum penny into circulation in the United States in 1973 was defeated in part by Pediatricians and Pediatric Radiologists concern that these new coins would not be easily identified on radiographs.33 Patients with retained lead foreign bodies can have statistically significant elevated blood lead levels as compared with matched controls.34
Foreign bodies have specific US characteristics. Smooth and flat surfaces typically produce a dirty shadowing or reverberation artifact.35,36 Irregular surfaces with a small radius or curvature produce a more clean shadow (Figure 98-1). Glass and metal typically produce a ring-down or reverberation artifact11,23,28,29,35,37 (...