Children commonly present to the emergency department (ED) with a subcutaneous foreign body (splinter, glass, etc.). Although rarely life-threatening, subcutaneous foreign bodies can be a source of frustration to patients, parents, and physicians, as well as being associated with potentially significant complications (1,2,3,4). Undetected foreign bodies often lead to repeat visits to the ED, additional expense, surgery, and, in extreme cases, substantial morbidity (5). In addition, missed foreign bodies comprise the second most frequent basis for malpractice claims filed against emergency physicians (6).

The detection and removal of subcutaneous foreign bodies is becoming easier and more efficient due to the increasing availability of portable, handheld ultrasonography in the ED. As more EDs become equipped with these devices, there is a need for emergency physicians to become well versed in their use. Ultrasonography has historically been used effectively for detecting ocular foreign bodies; evaluating extremities by delineating muscle groups, tendons, and vascular structures; and localizing foreign bodies preoperatively (7,8,9,10,11,12,13,14). It also has been used to localize and remove both radiopaque and nonradiopaque materials from extremities (1,10,14,15,16,17,18,19). More recently, studies have proved the utility of ultrasonography in evaluating foreign bodies in the mouth, head, and neck (20,21). Techniques for removing subcutaneous foreign bodies without the aid of ultrasound localization are discussed fully in Chapter 111.

Ultrasound offers the emergency physician an accurate, safe, and painless means of (a) determining if a foreign body is present, particularly if nonradiopaque; (b) performing precise preoperative three-dimensional localization; and (c) maintaining visualization during foreign body removal (7,9,13,16,22,23). It is particularly useful for confirming the presence of a foreign body in the pediatric population, as these patients are often unable or unwilling to provide a thorough history. In addition, once the foreign body is removed, ultrasonography can be used to determine whether it has been removed in its entirety (21), as wood, thorns, and some cactus spines tend to fragment both with the initial skin puncture and during removal (4,24).

Although it is not difficult to search for foreign bodies with ultrasonography, it does require patience, training, and the proper equipment. Definitive identification and removal of a foreign body with ultrasound requires practice. However, it has been demonstrated that physicians with no formal training in ultrasonography can be highly effective in detecting foreign bodies in clinical simulations (22).

The response of the body to a foreign object depends, in part, on the type of material present in the wound. If the body is unable to expel the foreign material, macrophages will attempt to digest it. If these mechanisms fail, fibroblasts will form a collagen capsule around it, resulting in a granuloma with associated hypervascularity and neovascularity (18). It is thought that subsequent capsular disruption secondary to trauma can result in delayed or recurrent inflammation (3,25).

Over time, retained subcutaneous foreign bodies can have variable effects on the surrounding tissues. Foreign body type and location affect potential complications. Glass, metal, and plastics are relatively inert and may produce minimal sequelae in the body. Conversely, organic materials, such as wood, tend to cause a pronounced inflammatory response. In addition, foreign bodies can migrate and result in neuropraxia, delayed rupture of nerves and tendons, and vascular injury (26,27,28,29).
They can also enter the circulation. Other complications are discussed in Chapter 111.

Whereas the visibility of objects on roentgenograms and CT scans depends on their density, ultrasonography detects differences in acoustic impedance between different tissues. The density of a medium multiplied by the velocity of sound through that medium determines its acoustic impedance. The greater the difference in acoustic impedance between two media, the more sound waves are reflected back toward the transducer to help produce an image. For example, the difference in acoustic impedance at the air-tissue interface at the surface of the skin is so great that virtually 100% of the sound is reflected and no image is produced. Thus, gel is used as a coupler to allow sound to enter into the tissues (3,30,31,32).

The ultrasound transducer not only produces sound waves but also serves as a receiver of the reflected waves. Objects in the path of the beam either reflect, absorb, or transmit sound. The stronger the reflected sound (echoes) returning from an object, the brighter the image produced. When the beam of ultrasound is perpendicular to the foreign material, more sound is reflected back to the transducer, and the dots comprising the image are brighter. Hence, a better image or a better artifact is usually seen when the beam is perpendicular to the object. Furthermore, when the reflection of sound is strong secondary to large differences in acoustic impedance, some returning sound is repeatedly reflected between the transducer and the object, much like the repeating echo heard when a person shouts in a canyon. This recurring reflection of sound between the transducer and the object is a reverberation that produces a “comet tail” artifact. Its appearance can be so striking that its presence can serve as a clear indication that a foreign body is present. This artifact, however, also can occur when air is present in the tissues, as the air-tissue interface represents a significant difference in acoustic impedance (3,9,15,30,31,33).

Small changes in beam orientation can have a great impact on the appearance of shadows, artifacts, or the imaging of the foreign object itself. For instance, tendons may appear echogenic if the beam is perpendicular or hypoechoic if the beam is oblique to the tendon. The size, shape, orientation of the object in relationship to the surface of the skin, and whether the object is in the focal zone of the transducer also will affect its ultrasonographic visibility (5,16,32,34,35). Although vessels are visible with gray-scale imaging, the addition of Doppler makes their identification much easier (9,11,16,36).

It cannot be overemphasized that the clinician needs to be familiar with the ultrasound equipment, the normal anatomy of the extremities, and the appearance of a variety of foreign bodies in longitudinal and transverse sections. The skin interface appears bright, with the soft tissues represented as more hypoechoic. Practice on normal hands and feet will increase comfort with the appearance of tendons, vessels, muscles, and bones. Scanning should be performed both at rest and with active range of motion (9,11,13). Differences can be noted in the appearance of a tendon or object when the ultrasound beam is oblique versus perpendicular to the normal anatomy. Beef or chicken models may be used to observe the characteristic echo patterns produced by different materials. As mentioned previously, these patterns can alert the ultrasonographer that a foreign body is present and also may provide clues as to the composition of the object. For instance, metal and glass are often associated with reverberation artifacts, whereas wood, pebbles, and sand can cause distal shadows (Fig. 136.1) (5,15,16,22,34,35). Organic materials often cause an intense inflammatory response, which can highlight the echogenic object by creating a contrasting darker background around the object. These hypoechoic halos around objects also can represent fibrinous exudates, collagenous capsule formation, abscesses, and granulation tissue (1,2,4,16,18). Further discussion of clinically important concepts in ultrasonography can be found in Chapter 132.

Foreign bodies are sometimes overlooked in the initial evaluation of soft tissue wounds in the ED (17). Physical examination usually identifies foreign bodies that are superficial and can be seen or palpated. Radiographs commonly identify those that are radiopaque. Radiopaque materials are commonly missed on initial examination because radiographs were never ordered (37). The history of an injury (e.g., an injury involving a thin or breakable object) or a physical examination consistent with retained foreign material, as well as the patient’s subjective opinion that a foreign body is present, are the best means for determining if a diligent search, including imaging studies, is necessary. Clinical findings associated with retained objects include localized tenderness, sharp pain with palpation, pain associated with a mass, discoloration beneath the surface of the skin, a chronic draining sinus, a nonhealing wound, an abscess with sterile purulent cultures, and persistent sterile monoarticular arthritis (2,3,4,23,28,38).