Brown Tumors Mimicking Diffuse Skeletal Metastases on F-18 FDG PET/CT and Bone Scintigraphy

Brown tumors are rare benign skeletal manifestations of hyperparathyroidism that may demonstrate intense 18F-FDG uptake and mimic metastatic bone disease on PET/CT. We report a case of primary hyperparathyroidism with markedly elevated parathyroid hormone levels and hypercalcemia. Prior Tc-99m sestamibi dual-phase parathyroid scintigraphy with subtraction imaging demonstrated persistent radiotracer retention in the right inferior parathyroid region, consistent with parathyroid adenoma. Bone scintigraphy suggested a metabolic bone process rather than metastatic disease, whereas subsequent 18F-FDG PET/CT revealed multiple intensely hypermetabolic skeletal lesions concerning for widespread metastases. In contrast, the suspected parathyroid lesion showed relatively low FDG uptake. Correlation of multimodality nuclear imaging findings with biochemical parameters favored the diagnosis of brown tumors, which was confirmed histopathologically as parathyroid adenoma. This case highlights the importance of integrating PET/CT, scintigraphic, and laboratory findings to avoid misinterpretation of FDG-avid skeletal lesions and unnecessary oncologic management.