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Emergency Ultrasound

Tips and Tricks: Ultrasound in the Diagnosis of Acute Appendicitis

Alice Chao, MD and Laleh Gharahbaghian, MD, FACEP

Acute appendicitis is one of the most common abdominal surgical emergencies. The diagnosis of acute appendicitis can be challenging, with a significant portion of patients initially misdiagnosed due to atypical clinical presentations and nonspecific laboratory tests. A delay in diagnosis increases the risk of perforation and, as a result, mortality rates.

The role of bedside ultrasound (US) by emergency physicians in the evaluation of appendicitis continues to evolve. Once appendicitis moved away from being a purely clinical diagnosis, physicians looked for the appropriate imaging modality that would be accurate, safe, cost-effective, and completed in a timely fashion. While computed tomography (CT) has been used most frequently due to its accuracy and availability, it falls short in other dimensions. The radiation from CT scanning is not ideal for pediatric or pregnant patients, and it is a costly imaging study. Ultrasound is thus an obvious alternative. One use of US in evaluating for acute appendicitis is to perform an US and, if equivocal, either discharge the patient with close follow-up or consult the surgical service depending on level of suspicion. Another approach is a 2-step imaging protocol, which starts with an US, then moves to CT if the US has equivocal results.[1, 2] In some institutions recently, this 2-step protocol has been replaced with focused magnetic resonance imaging (MRI).

Appendix US is both operator and patient-dependent. Sonographers with higher levels of experience and training have increased sensitivity in identifying the appendix. Few studies investigate the ability of EPs to successfully identify the appendix on US after a short training course. In one prospective study, the sensitivity of detecting appendicitis with point of care (POC) US was only 65% with a specificity of 90%, concluding that EP-performed bedside ultrasound was not sensitive enough to rule out appendicitis.[3] Chen et al, however, showed that EP-performed sonography for appendicitis had a sensitivity of 96.4% after completing a 5-day intensive training course in abdominal ultrasound.[4] Ultrasound of the appendix can be limited depending on the patient’s body habitus, anatomy, and amount of bowel gas obstructing the view. Here we describe the technique and some tips and tricks on finding the appendix by bedside US.

Technique

1. Patient position: supine.Appendicitis1

a. Tip: Have the patient bend their knees in order to relax the abdominal wall musculature for ease of compressibility.
b. Tip: Provide pain medication prior to scanning.

2. Probe: Either the high frequency linear probe or the curvilinear probe (if increased depth is required) can be used to detect the appendix.

a. Tip: When using the linear probe, choose the probe with the larger/wider footprint, which will allow better visualization of the regional anatomy. 

3. Technique: Place the probe in the right upper quadrant over the ascending colon with the probe indicator toward the patient’s right. Sliding inferiorly down to the right lower quadrant will reveal the cecum/terminal ileum and ultimately the appendix. Alternatively, the probe may be placed directly over the point of maximal tenderness, as indicated by the patient. 

Appendicitis2

Graded compression is applied to image the bowel; firm pressure is applied to bring the abdominal wall in contact with the psoas muscle every 1cm.

 

a. Tip: In the right lower quadrant, identify the psoas muscle and the transverse iliac vessels. Once found, the appendix usually lies just anterior to those structures. 

4. Appendix Anatomy: The appendix is a blind-ending tubular structure that normally will demonstrate peristalsis, is <6 mm in diameter, and is compressible. Click here for video

a. Tip: Once the appendix is found, scan in two orthogonal planes to ensure its tubular appearance; a lymph node may appear similarly yet will maintain an ovoid appearance. 

5. Appendicitis: Sonographic criteria for a diagnosis of appendicitis include a tubular structure that is > 6mm in diameter, noncompressible, and lacks peristalsis.Appendicitis3 Click Here for Video. There are several secondary signs of appendicitis that may be appreciated on ultrasound. A hyperechoic appendicolith within the lumen may be seen with posterior shadowing. Increased vascularity of the appendiceal wall may be appreciated as hyperemia with color flow Doppler, often referred to as the “ring of fire” on short axis. Finally, periappendiceal fluid collections may be seen suggesting edema or perforation.[5]

a. Tip: Make sure to evaluate the entire appendix to its tip, as there may be inflammation only present in the tip. In addition, adjacent abscess or evidence of perforation may be present only around the tip of the appendix

Elikashvili et al showed that the sensitivity of bedside US was not significantly different from that of radiology US (60% vs 63%) after a 30-minute lecture and 30-minute hands-on session. Use of bedside US also significantly decreased ED length of stay (LOS) (bedside US: mean LOS 154 minutes; radiology US: mean LOS 288 minutes; CT scan: mean LOS 487 minutes).[6] Not surprisingly, it has also been shown that US sensitivity and the rate of visualization of the appendix on US improved with more frequent use.[7]  

Conclusion
Though ultrasound diagnosis of acute appendicitis is not as sensitive as CT scans, the lack of radiation exposure and potential earlier time to diagnosis and disposition suggest that it should be attempted prior to exposing patients to radiation. Further practice by EPs will only improve diagnostic accuracy of acute appendicitis with bedside US and, as a result, improve the quality of patient care.

References

  1. Krishnamoorthi R, Ramarajan N, Wang NE, et al. Effectiveness of a staged US and CT protocol for the diagnosis of pediatric appendicitis: reducing radiation exposure in the age of ALARA. Radiology. 2011;259(1):231-9.
  2. Ramarajan N, Krishnamoorthi R, Gharahbaghian L, et al. Clinical correlation needed: what do emergency physicians do after an equivocal ultrasound for pediatric acute appendicitis? J Clin Ultrasound. 2014;42:385-394.
  3. Fox JC, Solley M, Anderson CL, et al. Prospective evaluation of emergency physician performed bedside ultrasound to detect acute appendicitis. Eur J Emerg Med. 2008;15:80-85.
  4. Chen SC, Wang HP, Hsu HY, et al. Accuracy of ED sonography in the diagnosis of acute appendicitis. Am J Emerg Med. 2000;18:449-452.
  5. Dawson M and Mallin M. (2014). Chapter 13: Appendicitis. Fox JC and Youssefian A, Introduction to Bedside Ultrasound: Volume 2 [iBook]. (pp 209-223).
  6. Elikahvili I, Tay ET, Tsung JW. The effect of point-of-care ultrasonography on emergency department length of stay and computed tomography utilization in children with suspected appendicitis. Acad Emerg Med. 2014;21:163-170.
  7. Mittal MK, Dayan PS, Macias CG, et al. Performance of ultrasound in the diagnosis of appendicitis in children in a multicenter cohort. Acad Emerg Med. 2013;20:697-702.



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