[Evaluation of CT, MRI and PET-CT in detecting retropharyngeal lymph node metastasis in nasopharyngeal carcinoma].
OBJECTIVE
At present, the detection of retropharyngeal lymph node (RLN) metastasis in nasopharyngeal carcinoma (NPC) mainly depends on imaging, but the diagnosis criteria are controversial. Recently, the 18F-fluoro-2-deoxy-D-glucose positron emission tomography ((18)FDG-PET-CT) has been widely applied in diagnosing cancer. This study was to evaluate CT, MRI, and (18)FDG-PET-CT in detecting RLN metastasis of NPC, and explore the imaging diagnosis criteria.


METHODS
From Dec. 2003 to Aug. 2005, 53 consecutive patients with NPC treated in Cancer Center of Sun Yat-sen University were enrolled. Contrast enhanced CT, MRI, and (18)FDG-PET-CT were performed on bilateral RLNs of the patients within 10 days before treatment. The diagnosis criteria of RLN metastasis for CT and MRI included single node with maximum diameter of > or =4 mm, and the presence of central necrosis or ringed enhancement; the criteria for (18)FDG-PET-CT included abnormal accumulation of irradiation in the RLN with the standard uptake value (SUV) of > or =2.5. Considering the response of RLN to clinical treatment, the differences of CT, MRI, and PET-CT in detecting RLN metastasis were compared.


RESULTS
Among the 106 intropharyngeal spaces of the 53 patients, the positive rate of RLN metastasis was significantly higher detected by CT and MRI than by PET-CT (39.6% and 45.3% vs. 20.8%, P<0.01), but the difference between CT and MRI was not significant (P>0.05). CT detected 27 cases of RLN metastasis with the maximum diameter of 0.4-0.9 cm, MRI detected 31 cases, and PET-CT only detected 5 cases. Especially, MRI detected 7 cases of RLN metastasis with the maximum diameter of < or =0.5 cm, CT detected 4 cases, but PET-CT detected none. CT detected 12 cases of RLN metastasis with the maximum diameter of > or =1.0 cm, MRI detected 14 cases, and PET-CT detected 13 cases. All patients were followed-up after treatment. One case of RLN metastasis with necrosis and the maximum diameter of 1.0 cm, and 1 case with the maximum diameter of 1.5 cm were eliminated within 6 months after treatment; the rest were eliminated within 3 months.


CONCLUSIONS
In detecting RLN metastasis in NPC, MRI has no obvious advantage over CT, while PET-CT is markedly inferior to CT and MRI, especially in detecting the cases with the maximum diameter of <1.0 cm. Furthermore, the metastatic RLNs with necrosis or the maximum diameter of < or =5 mm can't be detected by PET-CT. Setting the maximum diameter of > or =4 mm as a diagnosis criterion of RLN metastasis for CT or MRI is reasonable and feasible.
Su
Yong
Y
State Key Laboratory of Oncology in South China, Guangzhou, Guangdong, 510060, P. R. China.
Zhao
Chong
C
Xie
Chuan-Miao
CM
Lu
Li-Xia
LX
Sun
Ying
Y
Han
Fei
F
Wu
Hu-Bing
HB
Cui
Nian-Ji
NJ
Zeng
Zong-Yuan
ZY
Lu
Tai-Xiang
TX