Improved sonographic visualization of choledocholithiasis.

Ultrasonographic diagnosis of gallstones in the distal part of extrahepatic duct is not easy. A number of new techniques have been used by the authors to improve the detection rate of these stones. They include filling the duodenum and gastric antrum with drinking water, scanning after a fatty meal, and changing the patient's position during scanning. Ultrasound successfully identified choledocholithiasis in 78 of 104 patients for a sensitivity of 75%. There were 26 false-negative cases. The chief causes of the false negatives were obscuration of the distal duct by overlying bowel gas, missing of small stone in a nondilated bile duct, and misdiagnosis of soft pigment or an impacted stone having an atypical hypoechoic image in the distal duct as a tumor. False-positive diagnosis occurred in 32 out of 188 noncalculous cases, giving a specificity of 83%. These cases represent various hyperechoic lesions in the neck of gallbladder, cystic duct, and periampullary region. The overall diagnostic accuracy of gallstones in the extrahepatic bile duct by ultrasound was 80% (234/292).