鼻咽癌咽后淋巴结转移的CT、MRI和PET-CT诊断的对比研究

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（standard uptake value．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〉10．4cm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。

Evaluation of CT, MRI and PET-CT in detecting retropharyngeal lymph node metastasis in nasopharyngeal carcinoma

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 ((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.