Accuracy of ultrasound and oral cholecystography in assessing the number and size of gallstones: implications for non-surgical therapy

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Abstract
Prior to non-surgical therapy of gallstones it is important to assess their number and size. In order to evaluate the accuracy of ultrasound (US) and oral cholecystography (OCG) in counting and measuring gallstones, a prospective blind study was conducted to compare the results of US (n = 99) and OCG (n = 36), either alone or in combination (n = 34), with the number and size of gallstones retrieved after cholecystectomy. The number of gallstones was accurately estimated by US and OCG in 74% and 69% of the cases, respectively. In assessing the presence of up to three, five or 10 gallstones both US and OCG proved reliable. In measuring the size of gallstones, there was 19% accuracy with US compared with only 3% with OCG. With an accepted measurement error of 3 mm these values increased to 80% for US and 44% for OCG. US proved more reliable than OCG in discriminating gallstones smaller or larger than 10 mm and smaller or larger than 20 mm, but with US, detection of gallstones larger than 30 mm was problematic. Both US and OCG underestimated gallstone size. The combination of both techniques did not significantly improve the assessment of either number or size of gallstones compared with the results obtained with US or OCG alone. It is concluded that (1) both US and OCG have some limitations in assessing the number and size of gallstones, (2) the combination of both examinations does not improve accuracy, and (3) patient selection for non-surgical treatment of gallstones can be started by US alone.