Granulomatous Inflammation Mimicking Metastatic Malignancy on 18F-FDG PET/CT

18F-FDG PET/CT is an essential imaging modality in oncologic diagnostics, yet its limited specificity can pose challenges in differentiating malignancies from benign FDG-avid conditions such as granulomatous diseases. We present the case of a 67-year-old woman with systemic symptoms and widespread FDG-avid lesions in the liver, spleen, bones, and lymph nodes, initially suggestive of malignancy. However, extensive histopathologic evaluations from multiple sites revealed noncaseating granulomatous inflammation with no evidence of malignancy or infection. This case highlights the diagnostic complexity posed by granulomatous diseases on FDG PET/CT and underscores the importance of multisite tissue sampling in ambiguous cases.