Squamous Cell Carcinoma of the Palatine Tonsils: FDG Standardized Uptake Value Ratio as a Biomarker to Differentiate Tonsillar Carcinoma from Physiologic Uptake

Purpose: To quantify fluorine 18 (F-18) fluorodeoxyglucose (FDG) uptake in the palatine tonsils to identify a sensitive and specific metric for distinguishing physiologic asymmetric uptake from squamous cell carcinoma (SCC). Materials and Methods: This HIPAA-compliant retrospective study was approved by institutional review board. Informed consent requirements were waived. Twenty-six patients (seven female, 19 male; mean age, 53.46 years +/- 10.45 [standard deviation]) with tonsillar SCC were included. Twenty-six patients (seven female, 19 male; mean age, 61.77 years +/- 10.12) with head and neck carcinomas not involving the tonsils were included as control subjects. Tonsil standardized uptake values (SUVs) were measured bilaterally in each group. Independent-samples t test was used to compare mean SUVs, and Pearson correlation was used to evaluate association of FDG uptake between tonsils within control subjects. Results: The mean maximum SUV (SUVmax) of tonsil tumors was 9.36 +/- 4.54, which was significantly higher than that of contralateral cancer-free tonsils (2.54 +/- 0.88; P < .0001) and tonsils in control subjects (2.98 +/- 1.08; P < .0001). In patients with tonsillar cancer, the mean difference in SUVmax between tonsils was 10.43 +/- 7.07, which was significantly greater than that in control subjects (0.62 +/- 0.54; P < .0001). The mean SUVmax ratio between tonsils in patients with carcinoma was 3.79 +/- 1.69, which was threefold higher than in control subjects (1.18 +/- 0.13; P < .0001). For receiver operating characteristic analysis using SUVmax ratio to differentiate benign uptake from SCC, the area under the curve was 1.00 (95% confidence interval: 1.00, 1.00). A cutoff ratio of 1.48 had 100% sensitivity and specificity. Conclusion: The SUVmax ratio represents an accurate imaging biomarker for differentiating tonsillar SCC from physiologic F-18-FDG uptake. (C) RSNA, 2010