Temporal patterns of ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography sinonasal uptake after treatment of sinonasal malignancy

Background: Current guidelines have identified 10 to 12 weeks posttreatment as the ideal time-point for improved diagnostic accuracy of positron emission tomography/computed tomography (PET/CT) for deep tissue sites of the head and neck. After treatment, the sinonasal skull base is predisposed to prolonged inflammation that may render this time-point inappropriate for initial posttreatment imaging surveillance for sinonasal malignancies. The purpose of this study is to evaluate temporal trends in ¹⁸F-fluorodeoxyglucose (¹⁸FDG) sinonasal uptake after treatment for sinonasal malignancies to better elucidate the optimal time-point for initial PET/CT posttreatment evaluation in this patient population. Methods: A retrospective analysis of all successfully treated and non–locally recurrent sinonasal malignancies over a 15-year study period (2000 to 2015) was performed at our institution. Posttreatment ¹⁸FDG PET/CT standardized uptake value data were collected and compared between various time-points (2 to 4 months, 5 to 12 months, 5 to 24 months, and 13 to 24 months) using an independent-samples t test. Results: A statistically significant difference was noted between the posttreatment time windows 2 to 4 and 5 to 12 months (p = 0.048) as well as 2 to 4 and 5 to 24 months (p = 0.02). A trend toward significance was seen when comparing 2 to 4 and 13 to 24 months (p = 0.083). Conclusion: Our analysis of PET/CT in patients previously treated for sinonasal malignancy suggests that the posttreatment sinonasal skull base is characterized by a prolonged period of hypermetabolism that endures beyond the period previously described for deep tissue sites of the head and neck. These findings prompt a reevaluation of the previously described 10- to 12-week cutoff point for initial posttreatment PET/CT for head and neck squamous cell carcinoma as applied to sinonasal malignancies.