Differentiating between metastatic and inflammatory lymph nodes in adenocarcinoma of the lung by heterogeneity of 18F-FDG uptake

Objectives Lymph node (LN) characterization is very crucial which will determine the stage and treatment decisions in patient with lung cancer. Although 18F-FDG PET/CT has a high diagnostic accuracy in LN characterization than anatomical imaging, differentiating between metastatic and inflammatory LNs is still challenging because both could show high 18F-FDG uptake. The purpose of this study is to assess if the heterogeneity of 18F-FDG uptake could help differentiating between metastatic and inflammatory LNs in lung cancer.

Methods A total of 46 subjects adenocarcinoma of the lung, who underwent pre-operative 18F-FDG PET/CT without having any previous treatments and were revealed to have 18F-FDG-avid LNs, were enrolled. There were 56 pathology-proven metastatic lymph nodes in 28 subject. The pathology-proven metastatic LNs were compared to 43 pathology-proven inflammatory/benign LNs in 18 subjects. Coefficient of variation (CV) was used to assess the heterogeneity of 18F-FDG uptake by dividing standard deviation of standardized uptake value (SUV) by mean SUV. The volume of interest was manually drawn based on the combined CT images of 18F-FDG PET/CT (no threshold is used).

Results Metastatic lymph nodes tended to have higher CV compared to the inflammatory LNs. The mean CV of metastatic LNs (0.29+0.08; range: 0.11 - 0.55) was higher than that of inflammatory LNs (0.17+0.05; range: 0.07-0.30; p<0.05). On ROC analysis, area under curve was 0.897, and using 0.20 as cut-off value, the sensitivity and specificity were 87.5% and 79.1% respectively.

Conclusions In adenocarcinoma of the lung subjects having no prior treatments, metastatic LNs showed more heterogeneous 18F-FDG uptake than inflammatory LNs. Measuring CV of SUV derived from manual VOI can be helpful in determining metastatic lymph node of adenocarcinoma of the lung.