Ultrasonography

Sonography has been described in clinical case reports to identify soft tissue foreign bodies such as wood, fish bones, sea urchin spines, and other vegetative materials.1 1 and 15 However, this method has had a wide variation in sensitivity, specificity, and overall accuracy for the detection of soft tissue foreign bodies in experimental studies (see T.aMe 42.-1). Depending on the experimental model, the sensitivity for foreign body detection with ultrasound is 30 to 100 percent with a specificity of 70 to 90 percent.1516 and 17 In clinical practice, variation may be due to the size and sonographic nature of the foreign body, the presence of confounding objects (e.g., bone, blood, air, purulence, scars, old sutures) near or about the foreign body, and operator skill and experience. Areas with many echogenic structures such as calcifications, sesamoid bones, and tendons may hide foreign bodies within their acoustic shadows, so these areas must be scanned slowly to detect foreign bodies that are small or oriented perpendicular to the skin surface. Some areas of the body that are prone to foreign body penetration, such as the web spaces of the hands or toes, may not accommodate an ultrasound probe.

Once a foreign body is confirmed by plain films or CT studies, sonography can be used in place of fluoroscopy to guide an instrument to the object during retrieval. 18 The scanning beam should be oriented parallel to the long axis of a hemostat, which can be directed toward the long axis of the foreign body. Transverse and longitudinal scans provide views in multiple planes. A 7.5-MHz linear-array transducer can be used to find objects that are up to 3 cm deep.

The primary advantage of ultrasonography is that this imaging modality avoids radiation exposure. In addition, portable ultrasound machines are becoming increasingly available in EDs. The principal disadvantage of this modality is the variable sensitivity for foreign body detection for the reasons noted earlier.

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