An audit of ultrasound diagnosis of gallbladder calculi

Many series suggest that ultrasound is an accurate method for demonstrating cholelithiasis. However, these series were often prospective and the examinations performed by experienced sonographers. This audit addresses whether the accuracy is maintained in daily practice. We reviewed the ultrasound scans of 128 patients who underwent cholecystectomy for cholelithiasis and compared the findings. The operative and ultrasound findings were at variance in eight of the 128 patients (6.2%). Five were reported as having gallstones on ultrasound but none were found at cholecystectomy, a false positive rate for ultrasound of 3.9%. Three had abnormal gallbladders with no gallstones on ultrasound but gallstones were found at operation, a false negative rate of 2.3%. To avoid false positive diagnoses, suboptimal examinations should be repeated and the scan should be repeated immediately pre-operatively if only small calculi are seen. Alternative imaging should be performed if necessary, either cholescintigraphy in the acute situation or elective oral cholecystography. Some false negative examinations may be avoided by performing repeat examinations if the gallbladder is thick-walled and tender. With these provisos we conclude that ultrasound correctly diagnoses cholelithiasis in daily practice.