In total, 90% of ductal stones come from the gallbladder, with the rest arising from the duct itself. A total of 70% are cholesterol based; ...
In total, 90% of ductal stones come from the gallbladder, with the rest arising from the duct itself. A total of 70% are cholesterol based; they are pigment based if arising in the duct itself. Only about 10% are visible on CT. The biliary system is best imaged following a 4-hour fast (to distend the gallbladder).
US
• First line, good specificity (>95%).
• Shadow casting calculi in the gallbladder/bile ducts.
• Non-shadowing echogenicity is sludge (could also be blood or pus).
• Mimics include—gas, blood clots, clips, arterial calcification, parasites.
• CBD diameter less than 4 mm unlikely to contain any stones.
• EUS is most sensitive for detecting CBD stones.
CT
• Stone detected when surrounded by lower density bile.
MRCP
• Bile ducts clearly demonstrated on T2-weighted sequences, best seen in the coronal plane.
• Most sensitive, may be reserved where there is a low likelihood of stone.
• Stones are represented by low-signal filling defects.
• Not reliant on normal liver function.
• Risk of false negative with gas, blood and flow voids.
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