TYPE-II PNEUMOCYTIC DIFFERENTIATION IN AN ALVEOLAR ADENOMA OF THE LUNG - AN IMMUNOHISTOCHEMICAL STUDY

The alveolar adenoma of the lung is a rare benign tumor in which the n ormal parenchymal architectur is imitated by a proliferation of both t he alveolar epithelial cells and the mesenchymal septal cells. The fir st description, based on six cases, was published in 1986 by Yousem an d Hochholzer. From their ultrastructural findings they presumed a type II pneumocytes differentiation of the epithelial cells. We investigat ed an alveolar adenoma of the lung immunhistochemical by means of anti bodies against apoprotein B and C of human surfactant. Both the lining cells and the macrophages in the alveolar-like spaces were stained. T he septal connection tissue cells did not react. These findings confir m the expression of surfactant constituants and, hence, the differenti ation into type II pneumocytes of the epithelial cells of the alveolar adenoma.