18F FDG Uptake Due to Late-Onset Osteoradionecrosis for Tongue Base Carcinoma.

Differentiating osteoradionecrosis (ORN) from tumor recurrence is challenging. This report is rare documentation of false-positive F-FDG PET scan attributed to ORN in a patient previously treated for carcinoma of base of tongue (Ca BOT). Extraordinarily high F-FDG uptake was seen in right ramus (SUVmax, 17.4), left body mandible (SUVmax, 13.6) with left pleural deposits (SUVmax, 17.4). Tumor recurrence was suspected. Pleural fluid aspirate showed evidence of metastatic disease. However, CT-guided biopsy of mandibular lesions revealed necrotic tissue. Hence diagnosis of ORN was established. Patient was put on palliative chemotherapy. No mandibular recurrence was noted during 6-month follow-up period.