Clinical Ultrasound Is Safe and Highly Specific for Acute Appendicitis in Moderate to High Pre-Test Probability Patients

Daniel Corson-Knowles, MD; Frances M. Russell, MD


Western J Emerg Med. 2018;19(3):460-464. 

In This Article

Abstract and Introduction


Introduction: Clinical ultrasound (CUS) is highly specific for the diagnosis of acute appendicitis but is operator-dependent. The goal of this study was to determine if a heterogeneous group of emergency physicians (EP) could diagnose acute appendicitis on CUS in patients with a moderate to high pre-test probability.

Methods: This was a prospective, observational study of a convenience sample of adult and pediatric patients with suspected appendicitis. Sonographers received a structured, 20-minute CUS training on appendicitis prior to patient enrollment. The presence of a dilated (>6 mm diameter), non-compressible, blind-ending tubular structure was considered a positive study. Non-visualization or indeterminate studies were considered negative. We collected pre-test probability of acute appendicitis based on a 10-point visual analog scale (moderate to high was defined as >3), and confidence in CUS interpretation. The primary objective was measured by comparing CUS findings to surgical pathology and one week follow-up.

Results: We enrolled 105 patients; 76 had moderate to high pre-test probability. Of these, 24 were children. The rate of appendicitis was 36.8% in those with moderate to high pre-test probability. CUS were recorded by 33 different EPs. The sensitivity, specificity, and positive and negative likelihood ratios of EP-performed CUS in patients with moderate to high pre-test probability were 42.8% (95% confidence interval [CI] [25-62.5%]), 97.9% (95% CI [87.5–99.8%]), 20.7 (95% CI [2.8–149.9]) and 0.58 (95% CI [0.42–0.8]), respectively. The 16 false negative scans were all interpreted as indeterminate. There was one false positive CUS diagnosis; however, the sonographer reported low confidence of 2/10.

Conclusion: A heterogeneous group of EP sonographers can safely identify acute appendicitis with high specificity in patients with moderate to high pre-test probability. This data adds support for surgical consultation without further imaging beyond CUS in the appropriate clinical setting.


Acute appendicitis is inflammation of the appendix that can lead to perforation, abscess, other serious infections and death. Over 280,000 appendectomies are performed in the United States annually.[1] Although widespread availability of computed tomography (CT) has allowed more accurate diagnosis of acute appendicitis before reaching the operating room, this has come at the price of increased radiation exposure, increased cost and longer emergency department (ED) lengths of stay.[2–4]

Due to these risks, it is common to perform ultrasound examinations as the initial imaging modality in children to diagnose acute appendicitis.[5] Nonetheless, ultrasonography for appendicitis is not available in many EDs, and in most departments the availability of diagnostic ultrasonography is limited by the time of day.[6,7] Even when available, the accuracy of formal radiology ultrasound may be much lower in community practice than in academic centers where it is commonly studied.[8]

Previous studies have demonstrated excellent specificity of point-of-care or clinical ultrasound (CUS) for acute appendicitis among small cohorts of highly trained sonographers,[9–15] and incorporation of clinical risk-stratification with sonography has been shown to safely enhance diagnostic accuracy in a variety of settings.[16–20] However, the accuracy of ultrasound is highly dependent on the skills of the operator. This may be a barrier to implementation of CUS for appendicitis in new settings. The goal of this study was to determine if a heterogeneous group of emergency physicians (EP) could diagnose acute appendicitis on CUS. We hypothesized that EP sonographers could diagnose acute appendicitis with high specificity using a combination of clinical risk assessment, CUS, and self-assessment of image acquisition and interpretation.