The light microscopic and ultrastructural findings of a rare case of benign clear cell tumor of the lung were reported.
A routine chest X-ray film of an asymptomatic 42-year-old man revealed a coin lesion in the right upper lobe. Macroscopically, the round tumor was 3cm in diameter and was well demarcated from the surrounding pulmonary parenchyma. Microscopically, the tumor cells possessed clear cytoplasm containing large amounts of PAS positive granules (glycogen). Large sinusoidal vessels were observed among the tumor cells. Electron microscopically, the tumor cells showed characteristic cytoplasmic membrane-bound glycogen. Many tumor cells were surrounded by basement membrane-like material and were in contact with capillary walls. Some of the tumor cell had intracytoplasmic filaments. The ultrastructural findings suggested a smooth muscle or pericytic origin.