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Ovoid Shape of the Vermiform Appendix: A Criterion to Exclude Acute Appendicitis—Evaluation with US¹

¹ From the Department of Radiology II, University Hospital Innsbruck, Anichstrasse 35, 6020 Innsbruck, Austria (T.R., M.D., D.z.N.); Departments of Radiology (A.H., P.M., N.G.) and Surgery (K.S.), Hospital Barmherzige Brueder, Salzburg, Austria; and Institute of Biostatistics, University of Innsbruck, Austria (H.U.). From the 1999 RSNA scientific assembly. Received September 7, 2001; revision requested November 9; final revision received April 9, 2002; accepted April 30. Address correspondence to T.R. (e-mail: thomas.rettenbacher@uklibk.ac.at).

PURPOSE: To investigate whether the shape of the appendix in transverse section may be considered an ultrasonographic (US) criterion to exclude or confirm acute appendicitis.

MATERIALS AND METHODS: The shapes of appendices of 100 control subjects, of 174 patients with clinical suspicion of acute appendicitis but without acute appendicitis, and of 108 patients with acute appendicitis were prospectively evaluated with US. Definite diagnoses in patients with clinical suspicion of acute appendicitis were established and confirmed either with surgery and histologic examination in 161 patients or with clinical follow-up in 121 patients. Statistical measures such as sensitivity, specificity, positive and negative predictive values, and accuracy were assessed for the appendiceal shape as a diagnostic US criterion for acute appendicitis.

RESULTS: An at least partly round appendix indicated acute appendicitis with a sensitivity of 100%; specificity of 37%; positive and negative predictive values of 50% and 100%, respectively; and accuracy of 61%. In 67 of 174 patients with clinical suspicion of acute appendicitis but without acute appendicitis, the partly ovoid appendiceal shape aided in the exclusion of acute appendicitis, since it indicated a normal appendix with a probability of 86%. In 65 of 174 patients with clinical suspicion of acute appendicitis but without acute appendicitis, the ovoid shape over the entire appendiceal length excluded acute appendicitis with confidence.

CONCLUSION: The shape of the appendix in transverse section is a useful US criterion, since an ovoid shape over the entire appendiceal length reliably rules out acute appendicitis.

© RSNA, 2002

Index terms: Appendicitis, 751.291 • Appendix, US, 751.12981

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