P-BN20 An evaluation of the accuracy of sonography for the measurements of gallbladder polyps across 3 UK hospital trusts: should the surveillance guidelines be revised?

Background Transabdominal ultrasound scan (USS) is recommended for surveillance of gallbladder polyps (GBP), this is to stratify risk for premalignant potential. European Society of Gastrointestinal and Abdominal Radiology make recommendations based on increases of as small 2mm during sequential USS surveillance. Our aim is to determine the accuracy of USS in diagnosis and measurement of GBP. Methods Measurement data for all GBPs were gathered for three hospital trusts across a 12 year period and retrospectively reviewed. USS findings (diagnosis of GBP and GBP size) were compared with histological diagnosis and measurements, when both reports were available, in those patients who had underwent cholecystectomy at the time of data collection. Results For the first two hospital trusts, 778 USS were reviewed which identified patients with GBP. 78 patients had undergone cholecystectomy at time of data collection. Only 17/78 of patients had histological evidence of GBP.  Of those without GBP, 37/61 had gallstones. For the third hospital trust, 41 GBP histological reports were identified, 20 could be directly compared with USS. Collectively 29 USS reports were directly compared with GBP histology reports. Only, 31% had results which were in agreement to within 1mm. The mean measurement discrepancy between both modalities was 5.41mm. Conclusions USS does not provide an accurate diagnosis of GBP, it is likely that USS misdiagnoses gallstones as GBP.  Moreover, when comparing USS measurements with histological data, there is 31% accuracy of measurement to within 1mm in this cohort. Current guidelines recommend cholecystectomy if there is an interval change of 2mm or more; this data shows a measurement error of more than this.