A case of autoimmune pancreatitis mimicking a metastatic pancreatic tumor of rectal carcinoma

Abstract

A-72-year-old female was referred to our hospital in January 2008 for a suspected lung tumor. She had undergone abdominoperineal resection for rectal carcinoma 2 years previously followed by adjuvant chemotherapy. FDG-PET and MRI revealed a pancreatic mass with moderate FDG uptake as well as a pulmonary tumor. These imaging modalities yielded a diagnosis of concurrent metastases of rectal carcinoma. Distal pancreatectomy and splenectomy in this month and subsequently thoracoscopy-assisted partial lobectomy in April were performed for these lesions. The pulmonary lesion was histopathologically proven as metastasis of rectal carcinoma, however, the pancreatic mass showed IgG4-positive plasmacyte infiltration and fibrosis, with no metastatic cancer cells, suggesting autoimmune pancreatitis. The differential diagnosis of focal autoimmune pancreatitis is very difficult, especially in patients with previous/concurrent malignancy as ours.