IgG4-Related Hepatic Inflammatory Pseudotumor With Extensive Portal Vein Thrombosis Mimicking Hepatocellular Carcinoma.

IgG4-related disease is a systemic fibroinflammatory condition that can involve any organ and frequently mimics malignancy. Hepatic manifestations are uncommon, and mass-forming lesions with portal vein involvement are exceedingly rare. We report a 72-year-old woman who presented with abdominal discomfort, anorexia, weight loss, and newly identified portal vein thrombosis in the setting of hepatic masses. Magnetic resonance imaging demonstrated a 5.6-cm heterogeneously enhancing hepatic lesion with cystic and necrotic components and thrombosis of the main and right portal veins, raising strong suspicion for hepatocellular carcinoma. Significant radiologic-pathologic discordance resulted from the initial biopsy, which only showed chronic venous outflow obstruction. The repeat biopsy revealed extensive storiform fibrosis, many IgG4-positive plasma cells, and obliterative phlebitis, supporting the diagnosis of IgG4-related hepatic inflammatory pseudotumor. Prednisone treatment (0.6 mg/kg/d) resulted in a significant regression of portal vein thrombosis and hepatic lesions, as well as a rapid clinical improvement and normalization of liver functions. This case highlights the importance of repeat tissue sampling when imaging strongly suggests malignancy, but histology remains inconclusive and underscores the dramatic steroid responsiveness of IgG4-related hepatic disease.