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The Speed of Sound

The Speed of Sound: Ultrasound Trumps X-Rays at Identifying Foreign Bodies

Martinez, Rebecca MD; Butts, Christine MD

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doi: 10.1097/01.EEM.0000428253.17470.ea
    Image 1
    Image 1:
    Image 1. A needle viewed in long axis within the muscles of the neck. It is distinguished from the surrounding tissues because it is strongly echogenic (white). Slight movements of the transducer will reveal reverberation or comet tail effects, which are characteristic of metal or glass foreign bodies.

    A 40-year-old woman presents to the ED from the neurology clinic after having a needle break off in her left lateral neck during a procedure. She is anxious, but has no complaints, and her vital signs are stable. The patient asks if the ED can remove the needle without surgical intervention. Bedside ultrasound is applied to the area in question. (Image 1.)

    A patient with a possible retained foreign body can be a source of frustration for emergency physicians. Plain radiographs may fail to reveal the objects, and fare poorly in clearly localizing them. This may result in a time-consuming and frustrating search that may endanger underlying structures such as nerves or vessels.

    Foreign body identification with ultrasound is useful to identify not only radiopaque foreign bodies but other objects as well. Radiolucent objects, such as wood or plastic, can be easily missed on standard x-rays, but foreign bodies usually appear hyperechoic (white) when viewed with ultrasound. Metal and glass foreign bodies produce reverberations or comet tail effects (Image 2), and wood or plastic objects produce shadowing effects (Image 3).

    A high-frequency transducer should be used to obtain the best resolution possible because some objects can be difficult to differentiate from normal tissue. A stand-off pad can be made by placing gel in a glove and applying it to the area to improve visualization in hands and feet. Placing an extremity in a water bath also allows better sound transmission and a better view of the object. Once located, the depth, size, and orientation of the object can be evaluated. Surrounding structures also can be evaluated for nerves or vessels that should be avoided if removal of the foreign body is attempted in the ED.

    Image 2
    Image 2:
    Image 2. A glass foreign body within the soft tissue demonstrates the reverberation effect emanating from the inferior aspect (arrow). This is typical of glass or metal foreign bodies, which helps identify them.

    To remove the foreign body, center the transducer over the object and mark the optimal site for incision, taking into consideration the depth and position of the object. Inject lidocaine into the area to be incised, and then make a lateral incision. Guide hemostats toward the foreign body while visualizing the object in the long axis. Once the foreign body is felt, grab it and slowly retract the object from the site. Attempt removal in the short axis if you are unable to locate the object in long axis. Another option, which is useful for small objects, is to use two needles to localize the object in the short and long axis by ultrasound. An incision can then be made down to where the two needles meet.

    Image 3
    Image 3:
    Image 3. The foreign body here — wood within the soft tissue — is less obvious, but it is identified by the shadow extending deep to the object.

    Bedside ultrasound is reliable for localizing foreign bodies and ascertaining their position and proximity to other important structures. Removing the objects at this point becomes much more straightforward than searching blindly. This technique can also save the patient further consultation and procedures. It requires some practice, but multiple studies prove that emergency physicians can be successful in using ultrasound at the bedside to find and remove foreign bodies.

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