Frequency and malignancy rate of incidental focal salivary gland lesions identified by 18F-fluorodeoxyglucose–positron emission tomography

Purpose: We aimed to evaluate the frequency and malignancy rate of incidental salivary gland lesions (ISGLs) in patients undergoing 18F-fluorodeoxyglucose (FDG)–positron emission tomography/computed tomography (PET/CT). Methods: Using a predefined algorithm, all descriptions of FDG–PET/CT scans performed in the North Denmark Region at the Department of Nuclear Medicine, Aalborg University Hospital from 1.12 2009 to 31.12 2019 were electronically searched for focal uptake in one or more salivary glands. Results: In total, 28,362 FDG–PET/CT scans were performed in the study period. ISGLs were found in 197 (0.7%). A total of 193 (98%) had parotid gland ISGL, and four (2%) had submandibular ISGL. No sublingual lesions were found. Ultimately, 117 patients (60%) were referred to the Department of Otorhinolaryngology–Head and Neck Surgery for evaluation. Fine needle aspiration biopsy was performed in 97 patients, and the most frequent cytopathology was Warthin’s tumour (n = 62). Two patients had verified malignancy: one with histopathologically proven acinic cell carcinoma and one with cytopathologically proven metastasis from an oral squamous cell carcinoma. Conclusions: Incidental salivary gland findings on FDG–PET/CT are rare, and the risk of malignancy is low. Patients with ISGL may be evaluated secondary to the primary disease, but special attention should be given to patients with prior or known head-and-neck malignancies and patients with symptoms from the salivary glands, including swelling.