Aim: To analyze the Negative Appendicectomy Rate (NAR) in a single tertiary health service, compare it to published data and analyze the impact of pre-operative imaging in acute appendicitis.

Methods: A retrospective cohort study of a single health service was performed for a single year. Search terms included ‘diagnostic laparoscopy’ and ‘appendicectomy’ (both laparoscopic and open). Demographic data was extracted. The primary outcome was NAR. Secondary outcomes included tumour incidence and imaging modality accuracy as defined by NAR. Data was excluded if there was no histopathological report available.

Results: A total of 820 cases were identified, with 736 operations being performed for suspected appendicitis. A total of 633 booked laparoscopic appendicectomies were included for analysis, yielding an NAR of 11.2%. Overall tumour incidence was calculated at 1.5%. No preoperative imaging, or cases which utilized ultrasound as the only imaging modality, produced NARs of 19.3% and 17.4% respectively. Use of Computed Tomography (CT) in males under 40 was associated with lower NAR (3.0%, p=0.01) but no statistical difference was found between no imaging and ultrasound-only in this age group. Ultrasound-only was better than no imaging for females of all ages (p<0.001) and CT alone did not improve NAR in those under 40 years old (p>0.05). Preoperative CT was overall statistically significant at correctly identifying appendicitis (OR 2.80, p<0.001), giving an NAR of 7.1%.

Conclusion: This study’s NAR is better than accepted rates, however, is still high when compared internationally. There is great potential in the use of preoperative imaging to further guide correct diagnosis and operative patient selection.