Large Idiopathic Mesenteric Necrotizing Granuloma Mimicking Metastatic Disease on FDG PET/CT

On restaging FDG PET/CT for an 81-year-old man with oral cavity cancer, a large FDG-avid mesenteric mass suspicious for either metastasis or second primary was incidentally noted. Surgical pathology showed necrotizing granulomatous inflammation without evidence of tumor. All stains were negative for microorganisms. An elastin stain was negative as well, which excluded an origin of damaged blood vessels or vasculitis. The patient had no prior abdominal surgery or known gastrointestinal disease. Granuloma always poses a dilemma in the interpretation of PET/CT, due to its high FDG avidity and mass-like appearance which mimics neoplastic disease.