• Young Lan Seo, Dae Young Yoon, Sora Baek, Kyoung Ja Lim, Eun Joo Yun, Young Kwon Cho, Woo Jin Bae, Eun Jae Chung, and Kee Hwan Kwon.
• Department of Radiology, Kangdong Seong-Sim Hospital, Hallym University College of Medicine, 150, Seongan-ro Gangdong-Gu, Seoul, 134-701, Korea.
• Eur Radiol. 2015 Jan 1; 25 (1): 171-7.

ObjectivesTo evaluate the prevalence and clinical significance of focal parotid lesions identified by (18)F- FDG PET/CT in patients with nonparotid head and neck malignancies.MethodsFrom 3,638 PET/CT examinations using (18)F-FDG conducted on 1,342 patients with nonparotid head and neck malignancies, we retrospectively identified patients showing incidental focal FDG uptake in the parotid glands. The diagnosis of parotid lesions was confirmed histopathologically or on imaging follow-up. Patient demographics, clinical features, maximum standardized uptake value (SUV(max)) on PET images, size and attenuation on corresponding contrast-enhanced CT images were assessed and correlated with the final diagnosis.ResultsThe prevalence of incidental focal parotid FDG uptake on PET/CT was 2.1% (95% CI 1.4 - 3.0%). Among 21 patients with focal parotid lesions confirmed histologically or on imaging follow-up, 7 (33.3%) had malignant lesions (all metastases) and 14 (66.7%) had benign lesions (four pleomorphic adenomas, two Warthin's tumours, one benign lymph node, one granulomatous lesion, six lesions without histopathological confirmation). There were no significant differences in age, sex, SUV(max) or CT findings between patients with benign and those with malignant lesions.ConclusionFocal parotid FDG uptake on PET/CT in patients with head and neck malignancy warrants further investigations to ensure adequate therapy for incidental parotid lesions.Key Points• The prevalence of parotid incidentaloma on PET in head and neck malignancy was 2.1% • The malignancy rate of incidental focal parotid FDG uptake was 33.3% • SUV max could not reliably differentiate malignant from benign incidental parotid lesions.

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