Institute of Nuclear Medicine, Università Cattolica del Sacro Cuore, Largo A, Gemelli, 8, 00168 Rome, Italy.
World J Surg Oncol. 2012 Apr 28;10:71. doi: 10.1186/1477-7819-10-71.
18F-fluoro-deoxy-glucose (18 F-FDG) positron emission tomography integrated/combined with computed tomography (PET-CT) provides the best diagnostic results in the metabolic characterization of undetermined solid pulmonary nodules. The diagnostic performance of 18 F-FDG is similar for nodules measuring at least 1 cm and for larger masses, but few data exist for nodules smaller than 1 cm.
We report five cases of oncologic patients showing focal lung 18 F-FDG uptake on PET-CT in nodules smaller than 1 cm. We also discuss the most common causes of 18 F-FDG false-positive and false-negative results in the pulmonary parenchyma.In patient 1, contrast-enhanced CT performed 10 days before PET-CT did not show any abnormality in the site of uptake; in patient 2, high-resolution CT performed 1 month after PET showed a bronchiole filled with dense material interpreted as a mucoid impaction; in patient 3, contrast-enhanced CT performed 15 days before PET-CT did not identify any nodules; in patients 4 and 5, contrast-enhanced CT revealed a nodule smaller than 1 cm which could not be characterized. The 18 F-FDG uptake at follow-up confirmed the malignant nature of pulmonary nodules smaller than 1 cm which were undetectable, misinterpreted, not recognized or undetermined at contrast-enhanced CT.
In all five oncologic patients, 18 F-FDG was able to metabolically characterize as malignant those nodules smaller than 1 cm, underlining that: 18 F-FDG uptake is not only a function of tumor size but it is strongly related to the tumor biology; functional alterations may precede morphologic abnormalities. In the oncologic population, especially in higher-risk patients, PET can be performed even when the nodules are smaller than 1 cm, because it might give an earlier characterization and, sometimes, could guide in the identification of alterations missed on CT.
18F-氟代脱氧葡萄糖（18F-FDG）正电子发射断层扫描与计算机断层扫描（PET-CT）联合使用可对未明性质的肺部实性结节进行最佳代谢特征分析。18F-FDG 对直径至少 1cm 的结节和更大的肿块具有相似的诊断性能，但对于直径小于 1cm 的结节，相关数据较少。
我们报告了五例肿瘤患者，这些患者在 PET-CT 上显示直径小于 1cm 的肺部结节存在局灶性 18F-FDG 摄取。我们还讨论了肺部实质中 18F-FDG 假阳性和假阴性结果最常见的原因。在患者 1 中，PET-CT 前 10 天行增强 CT 检查未发现摄取部位有任何异常；在患者 2 中，PET 后 1 个月行高分辨率 CT 检查显示充满致密物质的细支气管，被解释为黏液嵌塞；在患者 3 中，PET-CT 前 15 天行增强 CT 检查未发现任何结节；在患者 4 和 5 中，增强 CT 显示直径小于 1cm 的结节，无法定性。18F-FDG 随访显示，直径小于 1cm 的无法在增强 CT 中检测到、被误读、未被识别或无法定性的肺部结节具有恶性特征。
在所有五例肿瘤患者中，18F-FDG 均能对直径小于 1cm 的结节进行代谢特征分析，提示 18F-FDG 摄取不仅与肿瘤大小有关，而且与肿瘤生物学密切相关；功能改变可能先于形态异常。在肿瘤患者中，特别是在高危患者中，即使结节小于 1cm，也可以进行 PET 检查，因为它可能提供更早的特征分析，有时可以指导识别 CT 遗漏的改变。
