Markedly Elevated CA 19-9 in Type I Mirizzi Syndrome in the Absence of Malignancy: A Case Report.

Mirizzi syndrome (MS) is a rare complication of long-standing cholelithiasis in which an impacted gallstone causes extrinsic compression of the common hepatic duct. Markedly elevated carbohydrate antigen 19-9 (CA 19-9) is strongly associated with pancreaticobiliary malignancies, but severe benign biliary obstruction can also cause substantial elevations, presenting a diagnostic challenge. We present a 50-year-old man with acute obstructive jaundice, fever, right upper quadrant pain, and a serum CA 19-9 level of 1000 U/mL. Triphasic contrast-enhanced computed tomography confirmed Type I Mirizzi syndrome caused by an 11.9-mm gallstone impacted in Hartmann's pouch, with no evidence of malignancy. Due to dense adhesions obliterating Calot's triangle, the patient underwent subtotal (fenestrating) cholecystectomy. Postoperatively, cholestatic liver tests markedly improved, and CA 19-9 decreased to 153 U/mL, supporting a benign obstructive and inflammatory etiology. This case highlights the importance of considering Mirizzi syndrome in patients with obstructive jaundice and markedly elevated CA 19-9 to avoid misdiagnosis and unnecessary aggressive surgical intervention.