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The Speed of Sound

The Speed of Sound: Ultrasound Effective (and Less Radiation) for Diagnosing Appendicitis

Butts, Christine MD

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doi: 10.1097/01.EEM.0000422878.09706.78
    Ultrasound image of an inflamed appendicitis consistent with acute appendicitis
    Ultrasound image of an inflamed appendicitis consistent with acute appendicitis:
    Ultrasound image of an inflamed appendicitis consistent with acute appendicitis. This image demonstrates the typical transverse appearance of the appendix, which is rounded and resembles a “target.” A small area of anechoic (black) fluid can be seen surrounding the appendix. A direct measurement is not included in this image, but a diameter greater than 6 mm is consistent with acute appendicitis. Compression of an inflamed appendix will demonstrate that the fluid-filled lumen remains open and does not compress.

    A 25-year-old man presents to the ED complaining of pain in his lower abdomen for three days. He states that the pain initially began in his periumbilical area, and has now migrated to his lower abdomen. He describes subjective fevers, chills, and nausea.

    His blood pressure is 110/80 mm Hg, heart rate is 100 bpm, respiratory rate is 12 bpm, and his temperature is 100.8°F. His exam reveals significant tenderness to his right lower quadrant with rebound. A bedside ultrasound reveals acute appendicitis, a commonly suspected diagnosis in patients with abdominal pain. Many practitioners rely on computed tomography to make the definitive diagnosis in suspicious cases, but this approach may not be feasible or advised. Obtaining a CT scan frequently requires intravenous and oral contrast, which may be time-consuming, and growing concerns about the long-term effects of routine CT scans may cause the emergency physician to reconsider this modality.

    Bedside ultrasound of the appendix is typically considered a more advanced application, but it can be successfully performed by the emergency physician. Visualization of the features of acute appendicitis in the correct clinical scenario may allow the practitioner to make the diagnosis without additional imaging.

    An inflamed appendix is best visualized with a high-frequency transducer, which allows for sufficient resolution of the area and identification of the organ. This transducer will provide excellent resolution but limited depth of penetration, so bedside ultrasound of the appendix may be limited by patient habitus.

    A helpful starting point for the bedside sonographer to identify the appendix is to begin the exam at the area of maximal pain or tenderness. Alternatively, the transducer can be placed in the approximate location of McBurney's point. Gentle compression of the transducer should be applied to displace overlying bowel. The initial orientation of the transducer is less important because the orientation of the appendix is variable. The entire right lower quadrant should be scanned in both orientations.

    An inflamed appendix typically appears as a “target” in transverse because of edema within its walls. The characteristic finger-like shape of the appendix can be seen in the longitudinal orientation. The appendix can be differentiated from other segments of bowel by its blind end. The total diameter will be greater than 6 mm and the lumen will not compress with pressure because it is fluid-filled. Anechoic (black) fluid may be seen surrounding the area, particularly with advancing appendicitis. Application of color Doppler may reveal increased flow, secondary to hyperemia. Finding an appendix with these characteristics can help to confirm an appendicitis diagnosis, but not localizing the appendix does not rule it out because patient habitus, bowel gas, or atypical positioning may hide it from view. A normal appendix is frequently difficult to localize to rule out acute appendicitis. Further evaluation and management is warranted in cases where appendicitis is clinically suspected without clear sonographic evidence.

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