Classification of acute appendicitis and pathology

Purpose Acute appendicitis (AA) is amongst the most common causes of acute abdominal pain. In spite of progress based on risk stratifications, "negative" appendectomies are performed in up to 30% of patients whilst the appendix perforates in others. Preoperative classification of AA based on imaging is therefore recommended. The aim was to classify AA based on imaging (ultrasound/US, computed tomography/CT), surgical pathology, and/or histopathology in order to differentiate between complicated and uncomplicated AA. A new classification of acute appendicitis (CAA) shall be illustrated by typical US and CT images and be employed in a diagnostic and therapeutic algorithm. Methods Medline, Embase, and the Cochrane Library were searched. Any study after 1970, which investigated clinical scores, pathology, US, CT, magnetic resonance imaging, and treatment of AA, was included. Typical images were taken from the author's image database. Results Five main types of AA are defined, normal appendix (type 0), nonvisualised appendix (type X), uncomplicated AA (type 1), complicated AA without perforation (type 2), and complicated AA with perforation (type 3). The imaging modality is indicated by an additional letter, e.g., type p3b for free perforation on pathology. Standardised reporting of the appendix evaluation by US and CT is presented, as well as algorithms for AA management. Imaging features indicating imminent perforation, as well as likely recurrence, were both classified as complicated AA. Conclusion Imaging is mandatory in suspected AA. The CAA clearly separates uncomplicated from complicated forms of AA allowing nonoperative management in selected patients with uncomplicated forms of AA.