Diagnosing appendicitis with CT and ultrasound using prospective patient stratification by body mass index

Abstract

Purpose: To determine the accuracy of CT and ultrasonography (US) in diagnosing appendicitis in adults stratified to either modality on the basis of body mass index (BMI), a measure of body habitus. Methods: Seventy-two adults with suspected appendicitis and demonstrating atypical clinical features were prospectively stratified to either appendiceal CT or US based on BMI. Patients with BMI < 30 underwent US and with BMI ≥ 30 underwent CT. Outcomes were determined by surgery, the medical record, and clinical follow-up after 3 months. Results: Of the 72 patients enrolled, 30 (24 women and 6 men) underwent CT and 42 (35 women and 7 men) underwent US. The average BMI was 34 ± 4 among patients who had CT and 24 ± 3 among patients who had US. Of the patients who had CT scans, 4 had positive scans for appendicitis and all of these were proven at surgery to have appendicitis. The remaining 26 patients had negative CT scans for appendicitis. Twenty-two of these were subsequently proven either by surgery or clinical follow-up not to have appendicitis, while 4 were lost to follow-up. This corresponds to a sensitivity, specificity, positive predictive value, and negative predictive value of 100 %. Twelve ultrasound examinations were positive for appendicitis. Nine of these patients had appendicitis proven at surgery, 1 had a perforated Meckel's diverticulum, and 2 did not have appendicitis after clinical follow-up. Twenty-seven patients had negative ultrasound exams for appendicitis. However, 6 of these had appendicitis proven at surgery, 17 did not have appendicitis, and 4 were lost to follow-up. Three patients had ultrasound exams that were equivocal for appendicitis; of these, 1 had appendicitis and 2 did not. For US, this corresponds to a sensitivity of 60 %, specificity of 85 %, PPV of 75 %, and NPV of 74 %. Conclusion: This study suggests that CT is an accurate method of evaluating adults with suspected appendicitis who have BMI ≥ 30. Stratifying patients with BMI < 30 to US did not reproduce the results already reported in the literature.