Parotid incidentaloma identified by combined 18F-fluorodeoxyglucose whole-body positron emission tomography and computed tomography: findings at grayscale and power Doppler ultrasonography and ultrasound-guided fine-needle aspiration biopsy or core-needle biopsy

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Abstract
Twelve parotid incidentalomas in 10 consecutive subjects (nine with a known malignancy elsewhere and one presumptively healthy subject) identified by combined 18F-fluorodeoxyglucose whole-body positron emission tomography and computed tomography (18F-FDG PET/CT) were investigated, with the aim of calculating maximum standardized uptake value (SUVmax) of each FDG-avid focus, and identifying corresponding sonographic and pathologic findings. The results of ultrasound-guided fine-needle aspiration biopsy (FNAB) (n = 9) and core-needle biopsy (CNB) (n = 3) were Warthin tumor in 10 cases, and pleomorphic adenoma and chronic inflammation in one each. SUVmax was 7.0–21.0 g/mL (average 13.7 g/mL) for Warthin tumor, 6.8 g/mL for pleomorphic adenoma, and 7.3 g/mL for chronic inflammation. Each FDG-avid focus corresponded to ovoid (n = 11) or lobulated (n = 1) hypoechoic mass on grayscale ultrasonography (US) and hypervascular mass, except one with chronic inflammation, on power Doppler (PD) US. Parotid incidentaloma identified by 18F-FDG PET/CT during workup of various malignancies elsewhere does not necessarily signify primary or metastatic malignancy, but indicates a high likelihood of benign lesions, particularly Warthin tumor. Such lesions should be evaluated thoroughly by US and ultrasound-guided FNAB or CNB if parotid disease would change the patient’s treatment plan.

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