Reactive type II pneumocytes in bronchoalveolar lavage fluid from adult respiratory distress syndrome can be mistaken for cells of adenocarcinoma.

A growing body of literature illustrates that bronchoalveolar lavage is a reliable and efficient means of diagnosing primary and secondary malignancies in the lung. Its safety in severely compromised patients often makes it preferable to other biopsy procedures. However, a variety of reparative and degenerative pulmonary disorders may result in cytologic alterations so severe that pneumocytes resemble cells of malignancy. We describe four patients with the adult respiratory distress syndrome from whom lavage fluid showed gland-like groups of malignant-appearing cells morphologically consistent with adenocarcinoma. Transbronchial biopsy sections in one case and lavage fluid electron microscopy in another showed that these pseudomalignant cells were reactive Type II pneumocytes with surface microvilli, cell junctions, and numerous cytoplasmic myelin figures. Careful clinicopathologic correlation is the best way to ensure accurate diagnosis in these cases.