Diagnostic Pitfall of ¹⁸F-FDG PET/CT: Unifocal Nonbacterial Osteomyelitis Mimicking Bone Metastasis

Chronic nonbacterial osteomyelitis (CNO) is a rare inflammatory bone disorder of unclear etiology that may present with unifocal or multifocal lesions. Because it can mimic malignancy on imaging, clinicoradiologic correlation and a multidisciplinary approach are essential. We report unifocal inflammatory osteitis compatible with CNO involving the sternum in a 56-y-old woman with a history of ductal carcinoma in situ. During surveillance, bone scintigraphy showed focal ^99mTc-methylene diphosphonate uptake and ¹⁸F-FDG PET/CT revealed a solitary ¹⁸F-FDG-avid sternal lesion. MRI findings were suggestive of osteomyelitis. Biopsy excluded malignancy, supporting a diagnosis of CNO. Follow-up MRI demonstrated regression. This case underscores that a solitary ¹⁸F-FDG-avid sternal lesion does not necessarily represent metastatic disease, and histopathologic confirmation may prevent unnecessary treatment escalation.