An Unusual Cause of Obstructive Jaundice

Abstract

Question: A 45-year-old man presented with painless obstructive jaundice for 1 month. His past medical history was unremarkable. Significant laboratory results included total bilirubin of 73.4 μmol/L (normal 5.1-20 μmol/L), direct bilirubin of 46.5 μmol/L (normal <6.1 μmol/L), alanine transaminase of 168.3 U/L (normal 9-50 U/L), alkaline phosphatase of 438 U/L (normal 50-135 U/L) and gamma-glutamyl transferase of 1321.6 U/L (normal 10-60 U/L). Abdominal ultrasonography showed a gallstone in the common hepatic duct with intrahepatic ductal dilation, and the gallbladder was atrophic. Contrast-enhanced computed tomographic (CT) scan in a dual-energy mode showed luminal distension of gallbladder neck (Figure A, white arrow), with hepatic hilar stenosis (Figure A, blue arrow) and bilateral intrahepatic ductal dilation. Coronal virtual monoenergetic image reconstruction at 40 keV clearly showed an intraluminal lesion with hypodensity in gallbladder neck (Figure B, red arrow). The spectral Hounsfield unit curve showed the decreased attenuation values of the lesion as the energy level decreased (Figure C). What is the most likely diagnosis? Look on page 197 for the answer and see the Gastroenterology website (www.gastrojournal.org) for more information on submitting to Gastro Curbside Consult. Dual-energy CT suggested that the lesion was a cholesterol gallstone. Magnetic resonance cholangiopancreatography (MRCP) was then performed and confirmed a stone (Figure D, white arrow) in the gallbladder neck, with external compression of the common hepatic duct and dilation of the intrahepatic biliary duct, highly suggestive of Mirizzi syndrome (MS). In addition, a long cystic duct running parallel to the common bile duct with low insertion was found. Subsequent cholecystectomy confirmed a 1.7-cm cholesterol gallstone in the neck of the gallbladder causing hepatic hilar stricture, which was consistent with MS. The patient had an unremarkable recovery. MS, as a rare complication of gallstone disease, refers to impaction of a gallstone in the gallbladder neck or cystic duct causing obstruction of the extrahepatic bile duct.1Abou-Saif A. Al-Kawas F. Complications of gallstone disease: Mirizzi syndrome, cholecystocholedochal fistula, and gallstone ileus.Am J Gastroenterol. 2002; 97: 249-254Crossref PubMed Google Scholar MS can be tricky and may mimic cholangiocarcinoma, especially when gallstones are radiolucent on conventional CT.2Chen Y. Chang C. Liu K. Mirizzi syndrome due to a large radiolucent gallstone.Am J Gastroenterol. 2016; 111: 599Crossref PubMed Scopus (2) Google Scholar With the ability to differentiate materials on the basis of their differential attenuation at 2 different energy levels, dual-energy CT can help to identify the composition of internal body constituents, such as gallstones. Previous studies have reported that dual-energy CT can increase the conspicuity of isoattenuating gallstones.3Soesbe T.C. Lewis M.A. Xi Y. et al.A technique to identify isoattenuating gallstones with dual-layer spectral CT: an ex vivo phantom study.Radiology. 2019; 292: 400-406Crossref PubMed Scopus (15) Google Scholar In this case, dual-energy CT was first used to diagnose MS, clearly showing the gallstone in the gallbladder neck as the cause of the hepatic hilar obstruction, and to provide a diagnostic clue to confirm MS. This technique can potentially reduce the need for further imaging, such as MRCP, leading to a reduction in imaging cost and time to diagnosis for selected patients.