Objective: To evaluate the prevalence and risk factors of occult intrathoracic lymph node metastasis on preoperative chest computed tomography (CT) in clinical N0 non-small cell lung cancer (NSCLC) patients.

Material and Method: We retrospectively reviewed 490 definitely diagnosed NSCLC cases. Eighty-three individuals who met the criteria for clinical N0 NSCLC were enrolled. CT findings of these patients were reviewed for tumor side, tumor location, lobar involvement, tumor size, and histology. Prevalence and risk factors of occult intrathoracic lymph node metastasis were analyzed by univariate and multivariate analysis.

Results: Eighty-three patients with confirmed clinical N0 NSCLC were evaluated, including 44 men and 39 women, ages ranging from 38 to 86 years (mean 65.27±11.27). Prevalence of occult N1-2 (intrathoracic) and N2 (mediastinal) lymph node involvement were 15.7% (13/83) and 8.4% (7/83), respectively. According to univariate analysis, risk factors for occult N1-2 disease were left-sided tumor (p = 0.038), left lower lobe (LLL) tumor (p = 0.045), and clinical T2 tumor (p = 0.028). By multivariate analysis, risk factors for occult N1-2 disease included LLL tumor (p = 0.031) and clinical T2 tumor (p = 0.036). Clinical T2 tumor was identified as a significant risk factor for predicting occult N2 disease (p = 0.033).

Conclusion: Prevalence of occult intrathoracic and mediastinal lymph node involvement in clinical N0 NSCLC patients were 15.7% and 8.4%, respectively. As such, preoperative cervical mediastinoscopy is recommended in N0 NSCLC patients with clinical T2 to rule out mediastinal lymph node involvement.

Keywords: Clinical N0 non-small cell lung cancer (NSCLC), Occult intrathoracic lymph node metastasis, Skip metastasis