Negative appendicectomy: evaluation of ultrasonography and Alvarado score
Background: High negative appendicectomy rates are no longer acceptable with improvements in imaging techniques and clinical prediction rules. The use of ultrasound and CT scan in addition to clinical assessment and blood investigations has greatly reduced the negative appendicectomy rate to less than 10%.
Objectives: The aim of the study was to determine the negative appendicectomy rate at the two major teaching hospitals in Harare and to evaluate the accuracy of the Alvarado score and ultrasound scan in diagnosing acute appendicitis.
Design: Prospective observational, cross sectional study
Setting: Parirenyatwa Group of Hospitals and Harare Central Hospital, in Zimbabwe
Materials and Methods: A total of 206 patients undergoing appendicectomy at the two major teaching hospitals in Harare were included in this study between June 2012 and May 2013. Information recorded included: age, sex, clinical features, investigations and treatment. Alvarado score was calculated from the data in the case notes and ultrasound scan results were also captured. All appendices removed at operation were sent for histopathological examination. Appendicitis was confirmed at histology. The positive predictive value of Alvarado score and sensitivity and specificity of ultrasound scan were calculated.
Results: The overall negative appendicectomy rate was 16.5%. The negative appendicectomy rate for men was 13.3% and that for females was 24.4%. The negative appendicectomy rate for Parirenyatwa Group of Hospitals was 19.0% and that for Harare Central Hospital was 12.1%. The mean age was 28 years (SD 12.8). Appendicitis was diagnosed commonly in the second and third decades of life. Sensitivity of ultrasound scan in diagnosing acute appendicitis was 89.5% with a positive predictive value of 77.2%. Females were 2.6 times more likely to have an ultrasound scan done to diagnose appendicitis than males. Alvarado score had a sensitivity of 95.3% with a positive predictive value of 90.3%.
Conclusion: The negative appendicectomy rate (16.5%) at the two University Teaching Hospitals in Harare is relatively high when compared with modern trends. Alvarado score had a high sensitivity (95.3%) and predictive value (90.3%). Ultrasound scan had a high sensitivity (89.5%) and a relatively low predictive value (77.2%) in diagnosing acute appendicitis. Regular use of these assessment modalities should contribute substantially to reduction in the negative appendicectomy rate in our practice.