Abstract:

Objective
 To determine whether the use of 18F-FDG PET/CT alters staging and management of nasopharyngeal carcinoma (NPC) when compared with MRI staging practice；and to explore the relation of standard uptake value (SUV) of 18F-FDG PET/CT and the pathological classification and T staging of NPC. Methods The study was performed retrospectively on a group of 41 patients with a new diagnosis of NPC. All the patients underwent whole body PET/CT scanning and head & neck MRI scanning within 3 weeks of each other. The AJCC protocol was introduced to stage NPC and the results of the PET/CT were compared with MRI based on pathologic diagnosis. Results ①Primary tumor: the accuracy of T staging of PET/CT was significantly higher than MRI (85.37% vs 60.98%, U=2.49，P< 0.05). According to the pathologic results, PET/CT downstaged 3 patients and upstaged 7 patients. In the patients with NPC, the SUV had  positive correlation with T staging (rs=0.706，P<0.05); the SUV in the patients with undifferentiated carcinoma was significantly higher than that in the patients with poorly differentiated squamous carcinoma (t=7.89，P<0.05). ②Lymph nodes metastases: among all the 41 cases, 139 lymph nodes were obtained. PET/CT correctly detected 72 positive lymph nodes and 56 negative lymph nodes, the sensitivity and specificity were 93.51% and 90.32%,respectively; while MRI correctly detected 60 positive lymph nodes and 51 negative lymph nodes, the sensitivity and specificity were 80.00% and 79.69%,respectively. The accuracy of N staging of PET/CT was significantly higher than MRI(92.09% vs 79.86%,U=2.93，P< 0.05) ③Distant metastases：Among the 41 patients, 2 patients with liver and bone metastases were detected by PET/CT, which missed by MRI. Conclusion  18F-FDG PET/CT stages NPC more accurately and sensitively than does MRI. 

Key words:  nasopharyngeal neoplasms;18F-FDG PET/CT;standard uptake value, magnetic resonance imaging, TNM staging