Association between high-resolution computed tomography findings and the IASLC/ATS/ERS classification of small lung adenocarcinomas in Japanese patients

Objectives: The detection rate of small pulmonary nodules has recently increased and new techniques have been developed to improve diagnostic yield. The IASLC/ATS/ERS classification demonstrated a difference in prognosis depending on the histological subtypes of lung adenocarcinoma. We evaluated the association between high-resolution computed tomography (HRCT) findings and the classification of these tumors. Methods: We reviewed the data of 220 lung adenocarcinoma (≤3. cm) patients who received complete resection with lymph node dissection in our hospital. From the HRCT findings, the tumors were classified into the following 3 categories: pure-solid nodules, part-solid nodules, or pure ground-glass opacity (GGO) nodules. Pathological invasion factor (PIF) was evaluated by the degree of blood vessel invasion, lymphatic permeation, and visceral pleural invasion. Results: The tumors were classified as pure GGO nodules in 16 patients, part-solid nodules in 91, and pure-solid nodules in 113 from the HRCT findings. Tumors were diagnosed as noninvasive or minimally invasive adenocarcinomas (NMIADs) in 44 patients, and invasive adenocarcinomas (IADs) in 176. Lymph node metastasis was present in 31 patients (14.1%) and PIF in 101 (45.9%). All pure-solid nodules were IADs with a high PIF frequency (75.2%) or with lymph node metastasis (26.5%). All pure GGO nodules were NMIADs or lepidic-predominant adenocarcinomas. Among the part-solid nodules, IAD was detected in 67.0% of the patients and PIF in 16.5%. The consolidation/tumor (C/T) ratio and consolidation size were associated with IAD (optimal cut-off values: 0.4 and 8. mm, respectively) and PIF (0.8 and 15. mm, respectively). Conclusions: The HRCT findings correlated with the IASLC/ATS/ERS classification and were useful for evaluating the histological nature of the tumors. Most pure-solid tumors had the potential for high-grade malignancy, including PIF and lymph node metastasis. For part-solid tumors, the C/T ratio and consolidation size were important for predicting PIF and for diagnosing IAD according to this classification.