Diagnosing appendicitis by ultrasonography was first described by Puylaert in the 1980s.1 However, many factors have prevented this modality from becoming standard of care in the diagnostic work-up of appendicitis. Its limitations were further highlighted in 1994 when Balthazar et al. reported on 100 cases of appendicitis, comparing ultrasound with computed tomography (CT) scanning; the study showed better accuracy, negative predictive value (NPV), and sensitivity with CT scanning.2
However, while CT scanning has become the standard of care in the diagnosis of appendicitis in both children and adults, its liberal use has come under fire recently because of the risk of malignancy due to its ionizing radiation.3 To prevent excessive radiation, multiple authors have proposed a protocol utilizing ultrasound as the first diagnostic modality for suspected appendicitis, followed by CT scan of the abdomen if the ultrasound is negative or equivocal.4-6 This algorithm is feasible because of the inherent testing characteristics of ultrasonography in appendicitis. A meta-analysis by Doria et al. lists the overall sensitivity of ultrasound as 88% and 83% and its specificity as 94% and 93%, for children and adults, respectively.7 These characteristics make ultrasonography a good “rule in” test to confirm appendicitis as its specificity rivals that of CT scanning in some studies.
Unfortunately, its poor sensitivity in comparison to CT does not allow it to be utilized as a good “rule out” test, necessitating additional testing if the ultrasound result is not positive for appendicitis. Ultrasound is more accurate for detecting appendicitis in the pediatric population because the abdominal musculature of children generally has less fat content.8-10
The opposite is true of CT scans, where intraperitoneal fat actually improves the diagnostic accuracy for appendicitis.11 In this way, the protocol of ultrasound first followed by CT scan is ideally suited to help avoid ionizing radiation in pediatric patients. However, in today’s overcrowded ED, time and inability to perform the ultrasound examination are commonly cited as reasons for not obtaining an ultrasound examination in patients with suspected appendicitis. The literature shows that nonradiologists can perform this examination and obtain specificities as high as radiologists, even during the “off hours” between 5 p.m. and 8 a.m., when there is traditionally no radiology backup.12