Pathological Study of Atypical Adenomatous Hyperplasia of the Lung

Recently, small peripheral lung nodules, including atypical adenomatous hyperplasia (AAH), detected on mass screening by CT have increased in numbers. In this study, clinicopathological characteristics of surgically excised AAH were reviewed. Nine cases of surgically excised AAH of the lung detected on mass screening with spiral CT were reviewed clinicopathologically. We analyzed these cases with regard to age, sex, location of tumors, the number of tumors, tumor size, appearance of CT and X-ray, operation method and pathology. AAHs were classified as low grade and high grade, and analyzed immunohistochemically by carcinoembryonic antigen (CEA) and anti-surfactant apoprotein mouse monoclonal antibody (PE10). Four patients were male and five were female. The average of patient ages was 63.5 years and 8 cases had a mass in the right lung and 1 case in the left lung. 7 cases had a solitary mass and 2 cases had multiple masses. The size of tumors varied in diameter between 0.7-15mm (mean 7.1mm). Chest X-ray did not reveal any shadows but chest CT revealed pulmonary nodules with ground-glass attenuation in all except one case. Four cases had low grade AAH and 5 had high grade AAH. All of the low grade AAH were pathologically similar to Noguchi's type A and the high grade AAH were similar to Noguchi's type A in 3 cases and to type B in 2 cases. All of the 9 cases showed positive immunostaining for CEA and PE10. The results suggest that it is difficult to differentiate AAH from bronchioalveolar carcinoma clinically. The cases with ground-glass opacity on chest CT should be resected for diagnosis.