A rare case of immunoglobulin G4-related periarteritis mimicking pancreatic cancer.

Immunoglobulin G4 (IgG4)-related disease (IgG4-RD) is a systemic inflammatory disorder characterized by abundant infiltration of IgG4-positive lymphocytes and plasma cells with fibrosis in the involved organs. Periarterial lesions are relatively rare manifestations of IgG4-RD, and their clinical and imaging findings remain unclear. A 66-year-old man presented with persistent upper abdominal pain. Contrast-enhanced computed tomography (CECT) showed a gradually enhanced 47 mm soft tissue mass lesion adjacent to the pancreatic uncinate and spreading around the superior mesenteric artery. Considering the imaging findings, pancreatic cancer could not be ruled out. We decided to perform an endoscopic ultrasound-guided fine-needle biopsy to confirm the histological diagnosis; however, we could not obtain a sufficient amount of tissue. Finally, the patient was diagnosed with IgG4-related periarteritis by performing a percutaneous biopsy of the lesion. The patient was treated with oral prednisolone (PSL) and approximately six months after PSL induction, CECT revealed marked shrinkage of the lesion. Although imaging findings are important for diagnosis, histopathological findings are essential for accurate clinical diagnosis. All possible means, including percutaneous targeted biopsy, should be attempted to acquire sufficient tissue to confirm the pathological diagnosis to enable appropriate treatment.