Normative Ranges for PET 18F-FDG Activity in the Head and Neck of Pediatric Patients

Background: Positron emission tomography (PET) with fluorine 18 fluorodeoxyglucose (18F-FDG) has been widely used for pediatric tumors. In order for 18F-FDG to confer utility in its widespread use, normal ranges encompassing physiologic variation must be elucidated, such that abnormal variation can be identified. Normal physiologic activity may vary according to age group. Previous studies investigating physiologic uptake in the head and neck organs have not focused on a pediatric population. Objective: The purpose of this study is to elucidate the normative values for 18F-FDG uptake for head and neck structures in a pediatric population known to have no head or neck pathology. Materials and methods: A total of 97 patients (43 females) ranging in age from 2.7 to 18 years old who had no history of head or neck malignancy/pathology (either at the time of study acquisition or on follow-up) were included in this retrospective study. PET/CT imaging was acquired approximately 60 minutes after injection of 5.18 MBq/kg (0.14 mCi/kg) 18F-FDG. Twelve head and neck structures including 1. Lingual tonsils, 2. Adenoid tissues (pharyngeal tonsils), 3. Palatine tonsils, 4. Soft palate, 5. Tongue, 6. Sublingual glands, 7. Parotid glands, 8. Submandibular glands, 9. Spine at the level of C1, 10. Thyroid gland, 11. Inferior concha and 12. Vocal cords were evaluated in this study. The region of interest (ROI) was drawn over these structures in the axial view and the maximum and mean SUV normalized to body weight were recorded. Results: Lingual tonsils, adenoid tissues, palatine tonsils and sublingual glands showed the highest uptake. The mean SUVmaxes ± SD were 2.67 ± 1.25 in lingual tonsils, 3.99 ± 1.56 in palatine tonsils, 3.04 ± 1.91 in adenoid tissues, and 3.00 ± 1.21 in the sublingual glands. Other head and neck organs showed a mild 18F-FDG uptake; the mean SUVmax was 1.52 ± 0.43 for inferior concha, 1.51 ± 0.45 for soft palate, 1.33 ± 0.38 for tongue, 1.45 ± 0.52 for parotid glands, 1.97 ± 0.66 for submandibular glands, 1.68 ± 0.51 for the spine at the level of C1, 1.24 ± 0.40 for the thyroid gland, and 1.55 ± 0.87 for the vocal cords. Conclusion: Adenoid tissues, lingual and palatine tonsils and sublingual glands show a moderate to high 18F-FDG uptake (mean SUVmax>2.5), while other small head and neck organs show a mild 18F-FDG activity. the uptake of 18F-FDG has been noted in a variety of tissues [1,3,7,12]. Specifically, areas in the head and neck that fit the profile of having a high concentration of lymphoid cells like Waldeyer’s ring have been demonstrated to show increased 18F-FDG uptake compared to other body tissues [1,3,7]. Therefore, in order for 18F-FDG-PET to confer utility in its widespread use, we must be able to delineate pathology from normal physiologic variation. Moreover, normal physiologic activity may vary according to age group. For example, palatine tonsils are more active and pronounced in children and adolescents, and atrophy in adulthood. This corresponds to higher 18F-FDG uptake for palatine tonsils in a younger age group [12]. Studies of physiologic uptake of 18F-FDG in head and neck structures have published normal 18F-FDG uptake values in structures Citation: Vali R, Seraji M, Rohringer T, Amirabadi A, Akbarian R, et al. (2019) Normative Ranges for PET 18F-FDG Activity in the Head and Neck of Pediatric Patients. J Nucl Med Radiat Ther 10: 406