Recurrent Nasopharyngeal Carcinoma Presenting as a Positron Emission Tomography False-negative Scan

Positron emission tomography (PET) is valuable for detecting locoregional recurrences of nasopharyngeal carcinoma (NPC) with a high sensitivity and fair specificity. A negative PET result is generally thought to confidently exclude the presence of a tumor. However, a false-negative PET scan is more dangerous than false-positive results because an undiscovered recurrent tumor may eventually lead to the patient's death without proper treatment. In this report, we describe a false-negative PET scan in a NPC patient with a recurrent tumor in the left cavernous sinus, presenting as a new onset of left 6^th cranial nerve palsy 1 year after irradiation. The first magnetic resonance imaging (MRI) and PET scan failed to disclose any abnormalities. The second MRI performed 3 months after the first scans demonstrated a new abnormal lesion in the left cavernous sinus, which had resolved in the following MRI after re-irradiation. Therefore, clinical observation with suggestive symptoms is still important, even with negative imaging results. Close follow-up with a series of imaging studies must be performed when indicated.