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Speed of Sound

Speed of Sound

Ultrasound to the Rescue When X-Rays Fail

Butts, Christine MD; Kathmann, Brett MD

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doi: 10.1097/01.EEM.0000461006.07836.a6
    Image 2. Ultrasound image of a foreign body within the subcutaneous tissues of the patient's forearm. The object is seen as a hyperechoic (white) linear structure (arrow) with edema surrounding the area (arrowhead).
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    Figure

    A 54-year-old man complains of a wooden splinter lodged deep in his left forearm. He reports that two days earlier he was installing wooden posts for his job when he felt a sharp pain.

    He denies any current pain, but has noticed redness and swelling to the area. His physical exam is significant for a 6 cm lesion over the left forearm with erythema and induration. An initial x-ray of the forearm shows no foreign body. (Cover.) A bedside ultrasound of the affected area, however, was performed (Image 2), and the foreign body was localized and removed. (Image 3.)

    Image 1. X-ray of the patient's forearm, demonstrating an absence of a visible foreign body.

    It is not uncommon for ED patients to complain of a suspected subcutaneous foreign body. Most EPs have experienced the frustration of attempting to localize and remove these objects, even when they appear tantalizingly close to the surface. X-rays have traditionally been the first-line modality to localize a foreign body, but this can be a challenge if the object is radiolucent, as in this case. Ultrasound can aid in identifying a foreign body when the suspected material is not visible on x-ray. Foreign bodies that are wooden, plastic, or made of organic material (catfish and porcupine spines, cactus needles) are identifiable on ultrasound but typically missed on x-ray.

    A high-frequency transducer should be used to image the affected area to generate the necessary resolution to distinguish foreign body from normal tissue. Most foreign bodies are typically seen as hyperechoic (white), and will demonstrate some posterior shadowing. Inflammatory changes around the foreign body can be identified as anechoic (black) or hypoechoic (dark gray), and can aid in identification. These changes will typically be seen after the object has been present for several hours. When in doubt, imaging the contralateral (unaffected) side can help to distinguish foreign body from normal anatomy. Patients can also frequently guide the EP by noting where they feel a foreign body sensation.

    Image 3. Wooden foreign body after removal from the patient's forearm.

    Ultrasound can also be used to guide removal. The EP should note the depth and size of the object on the screen. Obtaining an image of the object in its long axis (along its longest length) allows the EP to mark its location on the skin surface and to make the incision at the appropriate point. Once the incision has been made, ultrasound can also be used to guide removal by localizing the object relative to the probing hemostat or forceps.

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