Papillary adenoma of the lung with a peculiar raw macroscopic feature

We report a case of papillary adenoma of the lung with a peculiar raw macroscopic feature at intraoperative consultation. A 52-year-old man was admitted to our hospital for the evaluation of a solitary peripheral nodule in the left lower lobe which was detected with chest CT. When we took staples off from the stump of the partially resected lung in order to make a frozen section diagnosis, granular fragments leaked out from the stump. On the cut surface, the dark reddish and granular tumor grew expansively; however, hemorrhage and necrosis were absent. Histologically, granular fragments were mainly composed of papillary structures, which consisted of a single layer of cuboidal to low columnar cells with round to oval nuclei lining the surface of the fibrovascular cores. Characteristically, papillary structures lacked elastic fibers in the stroma and were packed within an elastic fiber framework derived from pre-existing alveolar structures. We considered that high intratumoral pressure might have made the granular fragments leak out of the stump as soon as we removed staples and that peculiar macroscopic findings before fixation may be a diagnostic clue for papillary adenoma.