Ultrasonography (US) examination of acute appendicitis (AA): diagnosis of complicated and uncomplicated forms and when US is not enough

Ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) have high diagnostic accuracy in the diagnosis of acute appendicitis. Nowadays imaging is part of the diagnostic algorithm of appendicitis and the advantages are demonstrated by the reduced negative appendectomies rates. US is the preferred first line imaging in acute appendicitis. The US diagnosis of complicated and uncomplicated appendicitis is well characterized by different signs but the paradigm of US to take in mind is that the non-visualization of the appendix cannot exclude acute appendicitis. In US, when the appendix is not visualized, or US is inconclusive, second-line imaging examination should be performed. The aims of this pictorial are 1. to illustrate the US signs of complicated and uncomplicated AA; 2. to describe the conditions in which other imaging modalities should be performed to reach a definitive diagnosis.