IgG4-related hepatic inflammatory pseudotumor complicated by actinomycosis during steroid therapy

For a 67-year-old man with diabetes mellitus, a 9-cm liver mass was found on CT during the diagnosticwork-up for weight loss and fever. Dynamic CT and MRI showed a layered pattern ofcontrast enhancement suggesting the imaging features of the solid inflammatory mass. Aftertissue diagnosis of immunoglobulin G4 (IgG4)-related disease by gun needle biopsy, steroidtherapy induced partial shrinkage of the mass on the follow-up CT at 4 weeks. On the 5-monthfollow-up CT with the maintenance of low-dose oral steroid medication, disease progressionwith invasion to diaphragm brought surgical intervention of right hemihepatectomy consideringthe possibility of combined malignancy. In the area of diaphragmatic destruction, focal actinomycosiswas complicated in the main mass of IgG4-related disease. We are the first to describea rare case of IgG4-related inflammatory pseudotumor, complicated by actinomycosis,showing an invasive nature that mimicked malignancy during steroid therapy in a diabetic patient.