The Clinical Significance of Incidental Parotid Uptake in a PET/CT Study: A Diagnostic Algorithm

Background: Patients diagnosed with cancer do not have sufficient clinical data for the management of incidental parotid lesions. We aimed to reveal the importance of randomized parotid lesions encountered during oncologic F-18 fluorodeoxyglucose positron emission tomography (FDG PET/CT) imaging in our clinical practice and the diagnostic algorithm of such lesions. Methods: We performed a database search of PET/CT records generated from 2009 to 2015 for “parotid” in reports of patients who underwent PET/CT examination for a known malignancy elsewhere, or cancer screening. Results: Incidental parotid FDG uptake on PET/CT had a prevalence of 1.1%. The incidence of parotid metastasis in our series was 36.4%, and 75% of them had malign melanoma metastasis. Of the 11 cases, 5 were of Warthin tumours, and Warthin tumours showed stronger GLUT1 expression than metastatic parotid lesions. Conclusion: In patients with malignancy elsewhere, focal involvement of FDG by the parotid gland, especially if malignant melanoma or SCC is absent, should not be considered a metastatic disease without histopathologic confirmation. If parotid disease would change the patient’s treatment plan and disease stage, the parotid lesion should be evaluated by additional methods, such as fine needle aspiration biopsy.