To identify variables associated with inconclusive ultrasound examination and the need for further abdominopelvic computed tomography (CT) examination for the diagnosis of acute appendicitis.

A total of 105 adult patients with acute appendicitis were included. There were 55 patients (38 men, 17 women; mean age, 23±9 [SD] years; range: 15–58 years) with a diagnosis of acute appendicitis using ultrasound alone and 50 patients (30 men, 20 women; mean age, 31±14 [SD] years; range: 16–83 years) who required further CT. Demographic, clinical, and biological criteria and appendix location were compared between the two groups to search for variables associated with the need of further CT.

Patients who required further CT were older (31.1±14 [SD] years) and had a greater body mass index (BMI) (26.7±4.3 [SD]kg/m²) than those who did not require CT (23±9 [SD] years and 22.9±3.4 [SD]kg/m²), respectively (P<0.01). A greater proportion of patients with complicated acute appendicitis was observed in patients who required further CT (9/50; 18%) than in those who had only ultrasound (1/55; 2%) (P=0.012). Atypical appendix location was more frequent in patients who required CT (19/50; 36%) than in those who had only ultrasound (6/55; 11%) (P<0.001). There were no significant differences regarding gender, inflammatory syndrome and hours of imaging (on call vs. working hours) between the two groups.

Advanced age, high BMI, atypical appendix location, and complicated appendicitis are associated with inconclusive ultrasound and the need for further CT to diagnose acute appendicitis.