鼻咽癌咽后淋巴结转移的CT、MRI和PET-CT诊断的对比研究

Evaluation of CT, MRI and PET-CT in Detecting Retropharyngeal Lymph Node Metastasis in Nasopharyngeal Carcinoma

背景与目的:目前,鼻咽癌咽后淋巴结转移的诊断主要依靠影像学检查,但诊断标准尚存在争议;18FDG-PET-CT近年日益受到人们的重视。本研究拟对比CT、MRI和18FDG-PET-CT检测鼻咽癌咽后淋巴结转移的差异,结合临床探讨鼻咽癌咽后淋巴结转移的影像学诊断标准和18FDG-PET-CT对鼻咽癌咽后淋巴结转移的诊断价值。方法:2003年12月至2005年8月,中山大学肿瘤防治中心收治的鼻咽癌患者53例进入研究。所有患者在治疗前10天内以同一固定体位,完成增强CT、MRI和PET-CT扫描检查。以横断面图像上咽后间隙内最大径≥4mm的独立肿大结节、中央坏死或环形强化作为CT/MRI诊断咽后淋巴结转移阳性的判定标准;肿大咽后淋巴结出现异常放射性浓聚,明显高于周围组织且标准化摄取值(standarduptakevalue,SUV)≥2.5为18FDG-PET-CT的诊断标准;并结合临床治疗后咽后淋巴结的消退情况,比较三者对咽后淋巴结转移的检出差异及诊断价值。结果:CT、MRI和PET-CT对53例患者106侧咽后淋巴结转移的检出率分别为39.6%(42/106)、45.3%(48/106)、20.8%(22/106),CT和MRI显著高于PET-CT(P<0.01);CT稍低于MRI,但两者间差异无显著性﹙P>0.05)。CT和MRI检出最大径0.4～0.9cm的咽后淋巴结转移分别有27例和31例,但PET-CT仅检出5例;其中MRI检出最大径≤0.4cm的咽后淋巴结转移7例,CT检出4例,PET-CT均未见放射性浓集。最大径≥1.0cm的咽后淋巴结转移,CT、MRI和PET-CT分别检出12、14和13例。所有患者均获随诊,1例最大径为1.0cm(合并坏死)和1例最大径1.5cm的咽后淋巴结在治疗后6个月内消退,其余均在放疗后3个月内消退。结论:对鼻咽癌咽后淋巴结转移的检出诊断,MRI较CT并无明显优势。对最大径<1cm的咽后淋巴结转移,PET-CT的检出率明显低于CT或MRI。对并发坏死或横径≤0.5cm的咽后淋巴结转移,PET-CT存在明显的局限性。以最大径≥0.4cm作为CT/MRI诊断鼻咽癌咽后淋巴结转移的阳性标准较为合理可行。

BACKGROUND ＆ 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 （^18FDG-PET-CT） has been widely applied in diagnosing cancer. This study was to evaluate CT, MRI, and ^18FDG-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 ^18FDG-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 ≥4 mm, and the presence of central necrosis or ringed enhancement; the criteria for ^18FDG-PET-CT included abnormal accumulation of irradiation in the RLN with the standard uptake value （SUV） of ≥2.5. Considering the respone 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 ≤〈0.5 cm, CT detected 4 cases, but PET-CT detected none. CT detected 12 cases of RLN metastasis with the maximum diameter of ≥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, espetially in detecting the cases with the maximum diameter of 〈1.0 cm. Furthermore, the metastatic RLNs with necrosis or the maximum diameter of ≤5 mm can＇t be detected by PET-CT. Setting the maximum diameter of ≥4 mm as a diagnosis criterion of RLN metastasis for CT or MRI is reasonable and feasible.