Early malignant biliary obstruction after microwave ablation of a central colorectal liver metastasis: a case report

Microwave ablation (MWA) for centrally located colorectal liver metastasis (CRLM) in hepatic segments 4 and 8 (S4/8) carries substantial biliary and vascular risks. Post-ablation jaundice is routinely attributed to benign thermal strictures, potentially delaying recognition of malignant biliary obstruction from tumour progression. This retrospective case describes a 55-year-old woman with KRAS-mutant, microsatellite-stable rectal adenocarcinoma presenting with metachronous central S4/8 CRLM, treated with ultrasound-guided MWA following neoadjuvant chemo-targeted therapy. Postoperative day 48 contrast-enhanced MRI revealed peri-ablation soft-tissue enhancement concerning for residual or progressive disease, alongside new intrahepatic metastases and hilar lymphadenopathy indicative of systemic tumour progression. Notably, the patient remained anicteric with normal liver biochemistry, despite mild thermal biliary changes on imaging. Cholestatic symptoms developed at POD 52, with progressive biochemical deterioration leading to overt obstructive jaundice by POD 70. ERCP with biliary brush cytology confirmed mid-common bile duct adenocarcinoma. Although malignant biliary obstruction of colorectal origin was most likely in this disseminated disease setting, no cytology cell block was available for immunohistochemical or molecular lineage verification. This case highlights the critical need for proactive biliary surveillance in high-risk KRAS-mutant central CRLM: early post-ablation imaging evidence of tumour progression warrants close monitoring, even in the absence of jaundice, to avoid misattributing subsequent biliary dysfunction solely to benign thermal injury.