我們報告了一位45歲鼻咽癌男性，接受根治性化學放射治療三個月之後，核磁共振的檢查顯示有多顆殘存頸部淋巴結，可是正子攝影並無明顯活性吸收。我們安排了改良式頸部淋巴廓清術之後，證明頸部淋巴結是經由鼻咽轉移來的惡性細胞。正子攝影呈現即使根治性治療後超過3個月，仍可能出現擊昏效應影像。在短時間的根治性治療後，功能性的檢查仍需謹慎小心。

We report the case of a 45-year-old man who received definitive chemoradiotherapy for nasopharyngeal carcinoma. Three months after chemoradiotherapy, head-and-neck magnetic resonance imaging (MRI) showed multiple residual lymph nodes with what appeared to be metastases in the neck. However, 18-fluoro-2-deoxyglucose positron emission tomography (FDG-PET) produced nonspecific findings. We performed a confirmatory modified radical neck dissection; and pathologic examination revealed metastatic carcinoma, consistent with nasopharyngeal origin. The dramatic false-negative results were obtained on FDG-PET images more than 3 months after chemoradiotherapy. We conclude that functional studies need to be interpreted with caution within short intervals after definitive chemoradiotherapy even after 3 months