Giant cell arteritis on 18F-FDG PET/CT

Purpose: We present a case of incidentally noted giant cell arteritis in a patient undergoing 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT imaging. The patient was originally referred to PET/ CT for staging of his renal transitional cell carcinoma. Methods: The patient was injected intravenously with 370 MBq of 18F-FDG. After a 60 min uptake period, PET/CT imaging was performed from the skull base to the mid thighs. Results: A small para-aortic node in the region of the surgical bed showed increased tracer uptake of concern for malignancy. In addition, there were several non-calcified pulmonary nodules present, also concerning for malignancy. Incidentally noted was diffusely increased tracer uptake throughout the aorta and a thickened aortic wall on CT images. Diffuse tracer uptake was also present in the proximal branches of the aorta, including the carotid, iliac, femoral, and subclavian arteries. The patient had biopsy proven giant cell arteritis. Conclusion: Increased 18F-FDG uptake by the aorta on PET/CT imaging is an abnormal finding that prompts a more thorough assessment for malignancy, and also can indentify important co-morbidities in cancer patients. Evaluation of aortic uptake should be a routine practice in the interpretation of 18F-FDG PET/CT scans.