Papillary adenoma of the lung. Histological and ultrastructural findings in two cases.

Two cases of papillary adenoma of the lung are presented along with results of histological and ultrastructural examinations. The tumors were encountered in two asymptomatic patients in a mass-survey chest X-ray examination. The chest X-ray films showed the tumors as well demarcated small lesions. Histologically, both tumors arose in the bronchioles and consisted of cuboidal cells resembling type II pneumocytes showing papillary growth with accompanying edematous connective tissue. Several tumor cells each possessed a large eosinophilic intranuclear inclusion. In case 1, ciliated cells and Clara-like cells were also present in the tumor. Ultrastructurally, most of the tumor cells had various numbers of lamellar bodies in their cytoplasm, indicative of type II pneumocytes, and some of case 1 showed features of Clara cells and ciliated cells. The intranuclear inclusions appeared as aggregates of tubular structures or had lamellar body-like features. These findings are identical to those of papillary adenoma arising from the bronchiole.