FDG-PET/CT pitfalls in oncological head and neck imaging

Abstract

ObjectivesPositron 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. 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. 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.MethodsWe 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).ResultsThe 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. 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.ConclusionsThe 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.Teaching points• Knowledge of key imaging features of physiological and non-physiological FDG uptake is essential for the interpretation of head and neck PET/CT studies.• Precise anatomical evaluation and correlation with contrast-enhanced CT, US or MRI avoid PET/CT misinterpretation.• Awareness of unusual FDG uptake patterns avoids overdiagnosis of benign conditions as malignancy.

Is integrated 18F-FDG PET/MRI superior to 18F-FDG PET/CT in the differentiation of incidental tracer uptake in the head and neck area?

“…Furthermore, symmetrical tracer uptake of Waldeyer's ring, the salivary glands, and the thyroid without morphologic correlate is frequently observed and does not indicate an underlying pathology (23,24). Another frequent cause for symmetrical tracer uptake is brown fatty tissue (22,25). Due to excellent spatial registration of the CT and MRI images and the PET dataset, symmetrical tracer uptake could be attributed precisely to the corresponding tissue in this study by PET/CT and PET/MRI.…”

“…Although Choi et al (28) found increased focal tracer uptake to be a strong predictor for malignancy, more recent studies showed that also benign nodules show a strong tracer uptake and that the frequency of malignant nodules is lower than initially reported (29). Still, focal asymmetrical 18 F-FDG uptake in the thyroid demands further investigation (25,29,30). Unfortunately, MRI is not superior to CT in the differentiation between benign and malignant thyroid lesions (31).…”

Dual-phase F-18 FDG PET–CT in staging and lymphoscintigraphy for detection of sentinel lymph nodes in oral cavity cancers

“…Most common places of the infection/inflammation such as oropharyngeal, laryngeal, and middle ear infections can also affect the LNs in the neck, resulting in increased FDG uptake [23]. This can cause misinterpretation that may lead to low specificity.…”

The Radiologist’s Approach to CUP

“…However, the study fi ndings are limited as the PET/MRI examination protocol focused on the abdomen and pelvis and only included the chest if suspicious lesions were detected on the prior PET/CT scan. Furthermore, PET/MRI detected more suspicious lesions, but there was no fi nal histopathological correlation to exclude false-positive and false-negative fi ndings which are known to occur in hybrid imaging [ 42 ]. Advantages of PET/MRI include the lack of ionizing radiation for the MRI component, which makes it an attractive tool for repeated examinations, particularly in younger patients.…”