Peribiliary Inflammatory Phlegmon Masquerading as Cholangiocarcinoma in Janus Kinase 2 V617F-positive Primary Myelofibrosis: A Multimodality Imaging Diagnosis.

Peribiliary inflammatory phlegmon arising from chronic portal venous thrombosis can produce a morphological replica of periductal cholangiocarcinoma at the hepatic hilum. We report a 68-year-old woman referred with an outside magnetic resonance imaging diagnosis of cholangiocarcinoma, in whom multimodality imaging reassessment demonstrated a 68 mm × 37 mm × 32 mm porta hepatis soft-tissue lesion encasing the biliary confluence. The common bile duct measured only 5 mm despite circumferential encasement, disproportionately limited for malignant transmural invasion. Color Doppler ultrasonography with pulsed-wave spectral analysis demonstrated low-velocity continuous venous waveforms within intralesional channels, confirming patent cavernous collateral vessels and excluding tumor neovascularity. Triphasic contrast-enhanced computed tomography (CT) showed absent arterial-phase enhancement, near-homogeneous portal-phase uptake, and mild delayed washout, in contrast to the progressive delayed enhancement of fibrotic periductal cholangiocarcinoma. Tumor markers were normal. Blood count showed thrombocytosis, neutrophilia, and anemia; Janus kinase 2 (JAK2) V617F mutation was confirmed in peripheral blood. Bone marrow trephine biopsy demonstrated grade III reticulin fibrosis with megakaryocytic hyperplasia, establishing primary myelofibrosis as the driver of chronic multivessel splanchnic venous thrombosis and cavernous transformation. The oncology referral was cancelled, and the patient commenced on ruxolitinib. Follow-up sonography at 3 months showed stable lesion morphology with identical Doppler characteristics, inconsistent with untreated malignancy. Spectral Doppler confirmation of venous intralesional flow, disproportionately limited biliary obstruction relative to ductal encasement, and an atypical CT enhancement profile can reliably distinguish peribiliary phlegmon from cholangiocarcinoma. When cavernous transformation is identified on CT, JAK2 V617F testing for myeloproliferative neoplasm should follow.