Head and Neck Cancer Soft Tissue Radiation Necrosis - Diagnostic Challenge

A 53-year-old man with T4aN2cM0 tongue base squamous cell carcinoma received definitive chemoradiation. FDG PET/CT at 6 weeks showed partial metabolic response with soft tissue air indicating radiation necrosis at primary site and complete response in the neck. At 9 weeks, contrasted CT showed worsening but nonenhancing ulceration, area biopsied demonstrating a minute carcinoma focus with treatment effect. At 12 weeks, PET/CT showed increased primary site uptake interpreted as disease progression; however, no viable tumor was found at salvage surgery. Because nonenhancing ulceration predicts pure radiation necrosis with no viable tumor, contrasted CT may guide treatment selection in challenging cases.