9 Name the characteristic sites of focally decreased and fo-cally increased fatty infiltration of the liver. How can they be differentiated from malignant hepatic processes?
9 Review the following three sonographic images. Write down the imaging plane and list your differential diagnosis of the findings. Include every abnormality since several pathologic processes are present.
The bile duct (66), comprising the common hepatic duct above the cystic duct insertion and the common bile duct below it, normally measures up to 6 mm at the level of the minor omentum, but luminal diameters between 7 and 9 mm are still within the range of normal (Fig. 34.1), particularly after cholecystectomy. A dilated duct (exceeding 9 mm in diameter) invariably becomes visible anterolateral^ to the portal vein (11) (compare p. 23). Even when the distal segment of the common bile duct is obscured by duodenal air (compare Fig. 17.3), a proximal intrahepatic obstruction (e.g., hepatic metastasis) can be sonographically distinguished from a distal obstruction (e.g., stone lodged at the papilla, lymphadenopathy in the lesser omentum, or carcinoma of the pancreas). The proximal obstruction distends neither gallbladder (14) nor common bile duct.
The small intrahepatic biliary ducts are parallel to the portal vein branches (11) and are normally invisible. They become visible along the portal veins when biliary obstruction has dilated the ducts, resulting in the double-barreled shot-gun sign (Fig. 35.3). Sonography is successful in up to 90% of cases in distinguishing between obstructive (ductal dilatation) and hepatocellular (no ductal dilatation) jaundice. Characteristically, a severe biliary obstruction (Fig. 34.2) produces a tortuous dilatation of the intrahepatic biliary ducts (66) that can assume the appearance of a towering antler. Cholestasis can increase the viscosity of the bile that can lead to the precipitation of cholesterol or calcium crystals (Fig. 34.3). This so-called "sludge" (67) can also be seen after prolonged fasting without biliary obstruction. Before diagnosing sludge, a thickness artifact (p. 10) should be excluded by obtaining additional sections and by turning and shaking the patient. The ERCP can drain a biliary obstruction by inserting a biliary stent (59). Alternatively, biliary drainage can be achieved with a percutaneous transhepatic catheter.
Stones are formed in the gallbladder (gallstones) because of an altered composition of the excreted bile. Depending on their composition, gallstones (49) can transmit sound almost completely (Fig. 35.3), float within the gallbladder (cholesterol stones) or, if high in calcium content, reflect sound to the degree that only the surface is visualized (Fig. 35.1). A stone is established if an echogenic structure can be dislodged from the gallbladder wall (80) by moving and turning the patient, in contradistinction to a polyp (65) (Fig. 35.2).
Some stones remain fixed at the gallbladder wall because of inflammatory processes, or become lodged in the infun-dibulum, rendering the differentiation between stones and polyps difficult. Acoustic shadowing (45) distal to such a lesion (Figs. 35.1, 35.3) indicates a stone. An edge effect of the gallbladder wall (45) (Fig. 35.2) must be carefully distinguished from stone-induced acoustic shadowing (compare Fig. 9.4) to avoid any misinterpretation. The polyp shown in this case (Fig. 35.2) should be followed for signs of growth to exclude any malignant process.
Intrahepatic cholestasis (Fig. 34.2) is not always a manifestation of malignancy and can be caused by obstructing stones (49) in the intrahepatic ducts (66) (Fig. 35.3). The prevalence of cholelithiasis is about 15%, whereby older
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