Differential diagnosis of a rare papillary tumor and mucinous adenocarcinoma

Ciliated muconodular papillary tumors are characterized as rare papillary tumors of the peripheral lung, and involve ciliated, goblet, and basal cell proliferation with mucin secretion. We report the case of a 76-year-old woman who had an irregular solid nodule in the lung on chest computed tomography during a health screening. A wedge resection was performed. Although the intraoperative cytological diagnosis was mucinous adenocarcinoma, the final histological diagnosis was ciliated muconodular papillary tumor. The postoperative course was uneventful, with no recurrence at 24 months after surgery. Cytological diagnosis of ciliated muconodular papillary tumor can be difficult because of its similarity to mucinous adenocarcinoma.