Challenges in F-18 FDG PET/CT: Benign Osseous Hypermetabolic Lesions

Introduction: The evaluation of F-18 FDG avid skeletal lesions remains a challenging diagnostic dilemma due to FDG avidity of benign skeletal lesion masquerading as malignant metastases. Often benign bony lesions are FDG avid during the “acute” phase of formation, therefore using age of the lesion as a discriminant is unable to assist in evaluation. Level of FDG accumulation, measured by SUV, is often unable to discriminate between benign and malignant lesions, due to both overlap of SUV determinations and partial volume effects of small lesions on SUV calculations. Over the past 15 years, since the clinical implementation of fusion PET/CT there has been progressive improvement in both the sensitivity and spatial resolution of both modalities, which allows for evaluation of smaller lesions. With these changes, the potential to identify small hypermetabolic osseous lesions improved, and likewise the confounding variable of mischaracterization of small benign lesions has likewise increased. A keen awareness of the confounding presence of F-18 FDG avid benign osseous lesions and familiarity with the CT characteristics and pathophysiology of these lesions provides the clinician with the tools to improve diagnostic accuracy. Mischaracterization of these lesions may result in both under staging and over staging of malignant disease, with resultant mistreatment of disease. This exhibit will show examples of common benign FDG PET avid osseous lesions and review the CT characteristics of these lesions including pathogeneses and distribution of common benign lesions including schmorl’s nodes, subchondral cysts, periarticular processes, fractures, osteomyelitis and degenerative changes. Understanding of these benign processes, along with the appreciation of their CT characteristics can increase confidence of interpretation and improve diagnostic accuracy when interpreting oncologic PET/CT.