PRIMARY INTRAPULMONARY THYMOMA - A CLINICOPATHOLOGICAL AND IMMUNOHISTOCHEMICAL STUDY OF 8 CASES

We describe eight cases of primary intrapulmonary thymoma occurring in seven women and one man between the ages of 25 and 77 years. Clinical ly, all patients had initial radiographic findings of a parenchymatous intrapulmonary mass without evidence of mediastinal involvement eithe r radiologically or at surgery. The lesions varied from 0.5 to 10 cm i n greatest diameter. Five tumors were located close to the hilum, whil e the other three were discovered deep within the lung and in subpleur al locations. In one case, the lesion appeared to arise endobronchiall y and infiltrate the surrounding parenchyma. In another case, in addit ion to the main hilar mass, there were two smaller tumor nodules found deep within the same lung. Histologically, the lesions were character ized by the classic biphasic cellular composition of thymomas, i.e., a n admixture in varying proportions of epithelial cells and lymphocytes . Four cases were characterized by sheets of lymphocytes admired with scattered epithelial cells that were separated by fibrous bands into l obules. Three cases were composed predominantly of sheets of epithelia l cells admired with scattered small lymphocytes and containing promin ent perivascular spaces. In two of these cases, focal areas of spindli ng of the cells were noted. One case was composed predominantly of a s pindle cell proliferation with perivascular spaces and numerous small lymphocytes. Immunohistochemical stains for keratin and epithelial mem brane antigen in six cases highlighted the epithelial cells scattered against the lymphoid cell background. Seven patients were treated by s urgery. In one patient the tumor was deemed inoperable at the time of exploration owing to extensive pleural infiltration and was treated by postoperative radiation; the lesion recurred locally in the pleura 8 years later. Clinical follow-up in three patients after surgical excis ion showed them to be alive and well without evidence of disease at 10 months, 2 years, and 8 years, respectively. Two of the patients had b een followed clinically for 2 and 4 years following discovery of their lung masses on routine chest radiograph before resection of their tum ors. Two patients died of unrelated conditions; in one of them, the le sion had been followed clinically for 6 years before surgery; this pat ient died 6 months later from coronary artery disease, without evidenc e of recurrence or metastasis. Our findings suggest that intrapulmonar y thymomas are slow-growing tumors that may respond well to surgical r esection when confined to the lung. As with their mediastinal counterp arts, invasive tumors will require additional treatment for the possib ility of recurrence of metastasis.