"Lights and shadows" in ultrasonography

The case of a 40-year-old male patient come to the emergency service with symptoms suspicious of biliary colic, is presented. Liver sonography was requested to evaluate the parenchyma, the gallbladder and bile duct caliber in the suspicion of lithiasis. During the examination a hyper-reflecting image with posterior shadowing was detected at the level of the gallbladder infundibulum. However, the shadowing was not typical of lithiasis. This aroused some doubts and the scan was repeated after some minutes: an absolutely normal infundibulum was visualized. The shadowing was therefore an artifact probably due to a partial volume effect of the air contained in the distended duodenum, in contact with the gallbladder. The formation process of the sonographic image is carefully analyzed with particular reference to the situations generating artifacts.