RESUMO
UNLABELLED: Importance of the problem. Atypical or precocious presentation of acute appendicitis in children causes false diagnosis. OBJECTIVES: To determine internal and external validity of ultrasonography for confirmation diagnosis of acute appendicitis. PATIENTS AND METHODS: Patients with suspicious acute appendicitis treated in 1998. They have been classified into two groups. Group 1: patients with appendicitis; Group 2: patients with non-specific abdominal pain. MATERIAL: Ultrasonography equipment (5 and 7.5 MHz). METHOD: Ultrasonography has been considered as positive when 3 or more of the typical signs of appendicitis have been detected. Analysis unit: positivity of the test and presence or absence of illness confirmed by histologic analysis of the appendix obtained through laparotomy. RESULTS: Number of patients selected for the work: 139. Middle age: 8 years-old (range: 2 to 14 years); 75% were males, 25% females. Patients included in group 1: 42; patients included in group 2:97. False positive rate was 12.23%, while false negative rate was 7.19%. Sensibility was 76%, specificity was 82%, positive predictive value was 65%, negative predictive value was 88% and precision was 80%. Odds-ratio pre-test: 0.43; Odds-ratio post-test: 0.64. CONCLUSIONS: Probability of accuracy diagnosis is duplicated by ultrasonography. Liability of the test is diminished by variability due to observer.