The role of F-FDG PET/CT for evaluation of metastatic mediastinal lymph nodes in patients with lung squamous-cell carcinoma or adenocarcinoma

Objectives

To evaluate the efficacy of ¹⁸F-FDG PET/CT in depicting metastatic mediastinal lymph nodes in patients with lung squamous-cell carcinoma (LSCC) or lung adenocarcinoma (LAC) in a tuberculosis-endemic country.

Methods

This study retrospectively reviewed patients with LSCC or LAC, who underwent preoperative ¹⁸F-FDG PET/CT to assess mediastinal lymph node metastasis. Patients with the short-axis of mediastinal lymph node ≤ 15 mm were included. PET/CT interpretation was analyzed in two ways. Firstly, with CT for anatomical localization, lymph nodes showing greater ¹⁸F-FDG uptake than vessel pool on PET were regarded malignant. Secondly, lymph nodes with positive uptake on PET were considered malignant, only when nodes had neither calcification nor higher attenuation than vessel pool on CT.

Results

One hundred and sixteen LSCCs and 234 LACs were evaluated. With CT for anatomical localization, the sensitivity, specificity, accuracy, positive predictive value (PPV) and negative predictive value (NPV) of PET were 78.6%, 45.5%, 53.4%, 31.4% and 87.0% in LSCC group, and 61.8%, 66.3%, 65.0%, 42.9% and 80.9% in LAC group. PET showed higher specificity and accuracy in LAC group compared with LSCC group (p = 0.001 and p = 0.038, respectively). Considering calcification or high attenuation on CT, the sensitivity, specificity, accuracy, PPV and NPV of PET/CT were 71.4%, 67.0%, 68.1%, 40.8% and 88.1% in LSCC group, and 54.4%, 86.1%, 76.9%, 61.7% and 82.2% in LAC group. Compared with PET, PET/CT possessed higher specificity and accuracy in LSCC group (p = 0.000 and p = 0.000, respectively), and higher specificity, accuracy and PPV in LAC group (p = 0.000, p = 0.000 and p = 0.022, respectively).

Conclusions

¹⁸F-FDG PET displays limited efficacy in assessing mediastinal lymph node metastasis with the short-axis diameter <15 mm in LSCC and LAC groups and higher false-positivity in LSCC group. The specificity and accuracy in LSCC and LAC groups are enhanced by interpreting attenuation characteristic on CT.