## Why option 1 is right Mirizzi syndrome, as depicted at **A**, is defined by extrinsic compression of the common hepatic duct (CHD) by an impacted stone in the cystic duct or gallbladder neck (Hartmann pouch). This high-level obstruction produces obstructive jaundice with a characteristic imaging finding: dilated intrahepatic ducts with a normal-caliber distal CBD. The curvilinear indentation on the lateral CHD wall seen on ERCP is pathognomonic. The anchor fact—impacted gallstone causing external compression of the CHD—directly explains the patient's presentation (Csendes A et al., Br J Surg 1989). ## Why each distractor is wrong - **Option 2**: This describes choledocholithiasis (a stone within the CBD itself), not Mirizzi syndrome. In choledocholithiasis, the stone obstructs the CBD directly from within, not from external compression of the CHD. The imaging would show a dilated CBD distal to the stone, not a normal distal CBD. - **Option 3**: This describes intrahepatic cholestasis with multiple stones (as in diagram **C**), which would present with diffuse intrahepatic ductal dilatation. Mirizzi syndrome is a single impacted stone at the cystic duct/gallbladder neck causing localized external compression, not diffuse intrahepatic disease. - **Option 4**: This describes a polypoid gallbladder mass (diagram **D**) with no ductal involvement. Such lesions do not cause biliary obstruction or jaundice unless they occlude the cystic duct lumen itself, and they would not produce the characteristic curvilinear indentation or high-level CHD compression seen in Mirizzi syndrome. **High-Yield:** Mirizzi syndrome = impacted cystic duct stone → extrinsic CHD compression → proximal biliary dilatation with normal distal CBD (the hallmark imaging finding that distinguishes it from choledocholithiasis). [cite: Csendes A et al. Mirizzi syndrome and cholecystobiliary fistula classification. Br J Surg 1989]
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