False positive fluorine-18 fluorodeoxy-D-glucose positron emission tomography finding caused by osteoradionecrosis in a nasopharyngeal carcinoma patient

Nasopharyngeal carcinoma (NPC) is treated by radiotherapy with or without chemotherapy. It is not uncommon to find the residual/recurrent lesion in the skull base area. For patients who had received radiotherapy, it is difficult to differentiate the skull base tumour from post-treatment change in the CT or MRI. ¹⁸F-2-fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) provides an alternative diagnostic choice in this situation for head and neck cancer including NPC especially when there is inconclusive CT/MRI finding. This report of an NPC patient who received radiotherapy 18 months previously, describes the misdiagnosis of tumour recurrence at the skull base found in both MRI and FDG PET scan. Histopathological studies showed osteoradionecrosis of the debrided tissue and follow-up PET showed complete regression of the skull base lesion. Therefore, a false positive result in FDG PET caused by osteoradionecrosis was confirmed. To the best of our knowledge, this is the first case report in the literature.