SP3.1.7 Performance of ultrasound in the diagnosis of cholecystitis and prediction of the “difficult cholecystectomy”

Aims Ultrasound has long been the radiological investigation of choice for right upper quadrant pain for the detection of gallstones and cholecystitis. However, previously reported sensitivity, specificity and other diagnostic metrics have varied widely and the underlying patient numbers have been small. We present robust and exhaustive diagnostic metrics based on a large series of 793 patients. Methods All laparoscopic cholecystectomies at our university hospital were prospectively logged between 2017 and 2020. The ultrasound findings, Nassar operative difficulty and histopathological findings were all collected in addition to patient biometrics. Results In our large patient series, sensitivity of ultrasound for cholecystitis was lower than previously reported at 75.7% for acute cholecystitis, 34.6% for chronic cholecystitis and 42.7% overall. Moreover, we show that sensitivity degrades with the time between ultrasound and cholecystectomy, falling below 50% at 140 days. Finally, we show that ultrasound strongly predicts Nassar difficulty grade of cholecystectomy and that its ability to do so is greatest where the interval between ultrasound and cholecystectomy is less than 27 days. Conclusions We present robust diagnostic metrics for ultrasound in the diagnosis of cholecystitis. These should caution the clinician that ultrasound may miss a quarter of cases of acute cholecystitis and over half of all cases of cholecystitis. Conversely, the finding of a thickened gallbladder on ultrasound can predict a “difficult cholecystectomy” and highlight the need for appropriate expertise and resources. Both this prediction and the diagnostic sensitivity are best if the ultrasound is done less than 27 days before cholecystectomy.