Intranuclear tubular structures observed in the cells of an alveolar cell carcinoma of the lung

Intranuclear tubular structures observed in the cells of an alveolar cell carcinoma of the lung are described. The structures were composed of membraneous tubules, measured about 60 nm in diameter, and had an electron-dense central core. These unusual structures were seen in the nuclei of neoplastic cells (Type II pneumocytes). The nature of the tubular structures remains unsolved, but morphologic characteristics and associated grnaulomatous reaction in the stroma imply the possibility of an unknown virus-like infection.