Intrahepatic bile ducts include capillary bile ducts, interlobular bile ducts, hepatic segments, hepatic lobe bile ducts, and the right and left hepatic ducts in the intrahepatic portion. The right and left hepatic ducts are primary bile duct branches, the left inner lobe, left outer lobe, right anterior lobe, and right posterior lobe bile ducts are secondary bile duct branches, and the remaining bile ducts of the liver segments are tertiary bile duct branches. Under normal circumstances, ultrasound can only detect the primary and secondary bile duct branches. If the ultrasound shows dilatation of the tertiary bile ducts or the interlobular bile ducts or capillary bile ducts, it suggests the presence of obstructive lesions. The bile secreted by the liver enters the common hepatic duct from the capillary bile ducts through the intrahepatic bile ducts at all levels, reaches the gallbladder to concentrate the bile, and then is discharged into the duodenum through the common bile duct. Due to the anatomical relationship between the left outer lobe and right posterior lobe bile ducts and the confluence of the common hepatic duct, it is more likely to lead to poor bile drainage, thus causing the formation of intrahepatic bile duct stones.