Purpose: To determine the frequency and natural course of mediastinal masses in asymptomatic people at high risk for lung cancer who were undergoing computed tomographic (CT) screening. Materials and Methods: Informed consent and institutional review board approval for this HIPAA-compliant study were obtained at each participating institution. All documented mediastinal masses among the 9263 baseline and 11 126 annual repeat screenings performed in the Early Lung Cancer Action Project (ELCAP) and its successor project, the New York ELCAP, were identified. Two radiologists confirmed all cases, identified the location and measured the diameter (average of length and width) of each mass, and reviewed all subsequent CT and clinical and surgical results. The prevalence and incidence of mediastinal masses were then determined. Results: Of the 9263 individuals, 71 had a mediastinal mass seen at baseline screening (prevalence of 0.77%). Of the 71 masses, 41 were thymic, 16 were thyroidal, two were esophageal cancers, six were tracheal-esophageal diverticula, and six were other masses. Among the 11 126 annual repeat screenings, only one new mediastinal mass was identified (incidence of 0.01%). This suggests a long average duration for mediastinal masses in asymptomatic people. Among the 41 thymic masses, five were larger than 3.0 cm in diameter, and all five were resected; of these five, one was a thymic carcinoma and four were noninvasive thymomas. Of the remaining 36 thymic masses, 25 were evaluated at follow-up CT 1 year later: Five had increased in diameter, two had decreased, and 18 remained unchanged. All 16 thyroid masses were due to goiter; none of these were changed at follow-up CT 1 year later. Conclusion: Mediastinal masses found in the context of CT screening for lung cancer in asymptomatic people should be approached in a "conservative" manner; this includes thymic masses smaller than 3 cm in diameter, as most of these remain unchanged or even decrease in size. (c) RSNA, 2006
