Intrapulmonary thymoma.

A 50-year-old man presented with a lung mass in the left upper lobe, which was shown by electron microscopy to be a thymoma. There was no evidence of a mediastinal mass. The lymphocytes of the tumor reacted with monoclonal antibody T101, a pan T-cell marker, and with OKT8. B1 and B2 surface antigens characteristic of B lymphocytes were not detected. Tumors of thymic epithelial cells completely covered by pleura without mediastinal involvement are rare.