Unexpected Fibrosing Mediastinitis Shown on FDG PET/CT in a Patient With IgG4-Related Disease.

A 66-year-old man presented to our hospital because of abdominal pain for 5 days. A contrast abdominal CT raised the possibility of pancreatic carcinoma. FDG PET/CT showed increased FDG accumulation not only in the pancreas and the retroperitoneum, but also in the posterior mediastinum, which was not typical of pancreatic carcinoma. The patient was subsequently diagnosed having immunoglobulin G4-related disease following the histopathologic examination.