Pulmonary oncocytoma: report of a case in conjunction with an immunohistochemical and ultrastructural study.

An intra-pulmonary mass in a 51 year old Japanese woman was incidentally discovered in the right middle lobe. The resected tumor was grossly well-demarcated, solid, light yellowish white in color and measured 3.0 x 2.0 x 1.5 cm in size. It was composed of a diffuse proliferation of large polygonal cells with an abundant, granular cytoplasm, and round to irregular nuclei with prominent nucleoli. Smaller eosinophilic cells with hyperchromatic nuclei and larger vacuolated cells were also observed. However, no mucin production was detected. There were neither argyrophilic nor argentaffin cells, and no serotonin-positive cells. They showed an immunoreactivity to cytokeratin and vimentin but not to alpha-actin. On electron microscopy, abundant microvilli, which have never been previously described in pulmonary oncocytomas, were observed. Occasional desmosomes and myelin figures as well as numerous mitochondria were also seen. No neurosecretory granules were present. These findings suggested that this tumor might have an epithelial origin from the bronchial serous gland with subsequent cellular degeneration.