Normal FDG uptake in the adenoids and palatine tonsils in children on PET/MRI

Background Information about the normal [F-18]2-fluoro-2-deoxyglucose (FDG) uptake in the adenoids and palatine tonsils in children is not available. Objective The purpose of this study was to report the range of standardized uptake values (SUVs) in the normal adenoids and palatine tonsils in children, assess for the degree of asymmetry between the right and left tonsils and evaluate for the correlation of SUVs between the adenoids and tonsils. Materials and methods Pediatric patients who had had an FDG positron emission tomography (PET)/magnetic resonance imaging (MRI) brain study in our institution from January 2018 to March 2019 were identified. Patients with a history of malignancy, adenoidectomy and/or tonsillectomy, incomplete imaging coverage of Waldeyer ring and the presence of artifact on PET/MRI were excluded. Two pediatric radiologists independently measured the mean and maximum SUVs of the right tonsil, left tonsil and the adenoids. Range, mean and standard deviation were calculated for all measurements. Ratios of SUV of the left to right tonsils and the adenoids to the tonsils were calculated. The paired t -test and Pearson’s correlation test were used for statistical analysis with a P -value <0.05 considered to be significant. Results Sixty-one PET/MRI brain scans were performed in our institution during the study period. After reviewing for exclusion criteria, 41 patients were included in the study (mean age: 10.1 years, range: 2–17 years; 19 boys and 22 girls). The mean SUV was 5.30±1.57 in the right tonsil, 5.25±1.53 in the left tonsil and 4.56±1.90 in the adenoids. The maximum SUV was 8.47±2.22 in the right tonsil, 8.45±2.18 in the left tonsil and 7.59±2.94 in the adenoids. The difference between the SUVs of the right and left tonsil was not statistically significant ( P =0.69 for mean SUV and P =0.90 for maximum SUV). There was a statistically significant moderately positive correlation between the FDG uptake in the adenoids and the right and left tonsil for both mean and maximum SUV ( r =0.36–0.41; P =0.008–0.022). Conclusion There is a wide variation of FDG uptake in the normal tonsils and adenoids in children. Uptake in the right and left tonsils is not significantly different. There is a moderately positive correlation between the FDG uptake in the adenoids and the tonsils.