Accuracy of MRI compared with ultrasound imaging and selective use of CT to discriminate simple from perforated appendicitis

Abstract

Background: Discrimination between simple and perforated appendicitis in patients with suspected appendicitis may help to determine the therapy, timing of surgery and risk of complications. The aim of this study was to estimate the accuracy of magnetic resonance imaging (MRI) in distinguishing between simple and perforated appendicitis, and to compare MRI against ultrasound imaging with selected additional (conditional) use of computed tomography (CT).

Methods: Patients with clinically suspected appendicitis were identified prospectively at the emergency department of six hospitals. Consenting patients underwent MRI, but were managed based on findings at ultrasonography and conditional CT. Radiologists who evaluated the MRI were blinded to the results of ultrasound imaging and CT. The presence of perforated appendicitis was recorded after each evaluation. The final diagnosis was assigned by an expert panel based on perioperative data, histopathology and clinical follow-up after 3 months.

Results: MRI was performed in 223 of 230 included patients. Acute appendicitis was the final diagnosis in 118 of 230 patients, of whom 87 had simple and 31 perforated appendicitis. MRI correctly identified 17 of 30 patients with perforated appendicitis (sensitivity 57 (95 per cent confidence interval 39 to 73) per cent), whereas ultrasound imaging with conditional CT identified 15 of 31 (sensitivity 48 (32 to 65) per cent) (P = 0.517). All missed diagnoses of perforated appendicitis were identified as simple acute appendicitis with both imaging protocols. None of the MRI features for perforated appendicitis had a positive predictive value higher than 53 per cent.

Conclusion: MRI is comparable to ultrasonography with conditional use of CT in identifying perforated appendicitis. However, both strategies incorrectly classify up to half of all patients with perforated appendicitis as having simple appendicitis. Triage of appendicitis based on imaging for conservative treatment is inaccurate and may be considered unsafe for decision-making. Presented to a scientific meeting of the Association of Surgeons of the Netherlands, Veldhoven, The Netherlands, May 2012; published in abstract form as Br J Surg 2012; 99(Suppl 7): S6.