Implication of the CT characteristics of subcentimeter pulmonary nodules

Screening by low-dose helical computed tomography (CT) detects many small pulmonary nodules less than 1 cm in diameter. Pulmonary nodules can be practically classified into three types by their CT appearance: pure ground-glass opacity (GGO), GGO with a solid central component, and solid nodule. Ground-glass opacity on thin-section CT is considered to most commonly represent focal bronchoalveolar carcinoma. However, one-third of pure GGOs represent atypical adenomatous hyperplasia. Noguchi has classified small adenocarcinomas into pathological subtypes (A through F) that appear to have clinical significance. Noguchi types D-F can be differentiated from types A, B, and C by CT findings--however, CT does not appear to be able to reliably distinguish D-F lesions and squamous cell carcinoma from benign tumors. The rate of obtaining a correct preoperative diagnosis on the basis of CT findings was significantly elevated after we instituted a program of preoperative evaluation based on defined thin-section CT characteristics of small nodules. Although emerging data suggest that limited resection for malignant lesions 10 mm or less may be appropriate, particularly for Noguchi types A-C, this remains controversial.