Renal Metastasis from Extrahepatic Cholangiocarcinoma Mimicking Renal Infarction: A Case Report and Literature Review.

Background: Cholangiocarcinoma (CCA) is a rare and aggressive malignancy of the biliary tree. Renal metastasis represents an exceptionally rare event, reported in fewer than 0.5% of cases. Its clinical and imaging presentation may closely mimic benign renal conditions, particularly renal infarction, posing a significant diagnostic challenge. Case Presentation: We report the case of a 72-year-old man who initially presented with intense right-sided flank pain without urinary symptoms. Combined imaging findings, including absent Doppler signal on ultrasound and absent contrast uptake on contrast-enhanced ultrasound (CEUS) in two-thirds of the right renal parenchyma, led to an initial diagnosis of right renal infarction. Seven months later, re-evaluation prompted by macroscopic haematuria, significant weight loss, cholestatic syndrome, and markedly elevated CA 19-9 revealed an invasive renal tumour mass associated with biliary ductal dilatation. Renal biopsy with immunohistochemical analysis (CK7+, PAX8-, c-kit weakly positive) confirmed renal metastasis from extrahepatic cholangiocarcinoma. The patient's clinical course was complicated by acute cholangitis, Clostridioides difficile enterocolitis, and upper gastrointestinal haemorrhage, requiring endoscopic retrograde cholangiopancreatography (ERCP) with biliary stenting, endoscopic ultrasound (EUS)-guided hepaticogastrostomy, and endoscopic haemostasis. Conclusions: A systematic review of the published literature identified only two previous dedicated case reports of renal metastasis from CCA, making this, to our knowledge, the third such case and the first involving an extrahepatic primary tumour presenting through its renal metastasis. This case highlights the diagnostic pitfall of mistaking hypovascular renal metastasis for renal infarction, the indispensable role of immunohistochemistry, and the importance of early percutaneous biopsy in avascular renal lesions without a confirmed thromboembolic aetiology.