Because FDG is not a tumour-specific tracer, it can accumulate in a variety of benign processes including benign tumours, inflammatory, post-traumatic and iatrogenic conditions. However, the interpretation of FDG-PET/CT studies in the head and neck may be quite challenging due to the inherently complex anatomy, physiological variants and unusual patterns of FDG uptake after radiation therapy and surgery. Thus, FDG-PET/CT tremendously facilitates the management of head and neck cancer patients in whom treatment is often expensive and associated with a significant morbidity. Further indications include assessment of post-treatment response, long-term surveillance to detect recurrence and, last but not least, detection of an unknown primary tumour. FDG-PET/CT is now routinely used in the head and neck for the delineation of the primary tumour, detection of regional nodal metastases, distant metastases and second primary tumours. Positron emission tomography-computed tomography (PET/CT) with fluorine-18-fluorodeoxy- D-glucose (FDG) plays a major role today in the pre-therapeutic work-up and post-therapeutic monitoring of patients with head and neck tumours. Awareness of unusual FDG uptake patterns avoids overdiagnosis of benign conditions as malignancy.Precise anatomical evaluation and correlation with contrast-enhanced CT, US or MRI avoid PET/CT misinterpretation.Knowledge of key imaging features of physiological and non-physiological FDG uptake is essential for the interpretation of head and neck PET/CT studies.The interpreting physician must be aware of these unusual patterns of FDG uptake, as well as limitations of PET/CT as a modality, in order to avoid overdiagnosis of benign conditions as malignancy, as well as missing out on actual pathology. False-negative findings are caused by lesion vicinity to structures with high glucose metabolism, obscuration of FDG uptake by dental hardware, inadequate PET scanner resolution and inherent low FDG-avidity of some tumours. The commonly encountered false-positive PET/CT interpretation pitfalls are due to high FDG uptake by physiological causes, benign thyroid nodules, unilateral cranial nerve palsy and increased FDG uptake due to inflammation, recent chemoradiotherapy and surgery. We review the pathophysiological mechanisms leading to potentially false-positive and false-negative assessments, and we discuss the complementary use of high-resolution contrast-enhanced head and neck PET/CT (HR HN PET/CT) and additional cross-sectional imaging techniques, including ultrasound (US) and magnetic resonance imaging (MRI). The purpose of this article is to provide a comprehensive approach to key imaging features and interpretation pitfalls of FDG-PET/CT of the head and neck and how to avoid them. However, interpretation of FDG PET/CT studies may be difficult due to the inherently complex anatomical landmarks, certain physiological variants and unusual patterns of high FDG uptake in the head and neck. Positron emission tomography-computed tomography (PET/CT) with fluorine-18-fluorodeoxy-D-glucose (FDG) has evolved from a research modality to an invaluable tool in head and neck cancer imaging.
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