A Case of Papillary Adenoma of the Lung

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Background. This report describes a case of papillary adenoma of the lung, which is an extremely rare benign epithelial tumor of the respiratory tract. Case. A 16-year-old girl was noted to have an abnormal lesion in the left lung in a mass screening chest X-ray examination. Computed tomography of the chest revealed a well-defined mass measuring 3.4×3.2 cm in the left lower lobe. We performed left lower lobectomy under video-assisted thoracoscopy to make a definitive diagnosis and for treatment. Histological examination revealed that the tumor consisted of columnar epithelial cells without nuclear atypia showing papillary growth around fibrovascular stroma. No elastic fibers were seen in the stroma. Immunohistochemistry showed that the epithelial cells were positive for surfactant apoprotein, pankeratin, epithelial membrane antigen, and nuclear thyroid transcription factor-1, while the Ki-67 labeling index was less than 4%. Electron microscopy revealed that the tumor cells contained lamellar inclusion bodies in their cytoplasm that were characteristic of type II pneumocytes. These findings led to a diagnosis of papillary adenoma of the lung with pneumocytic differentiation into type II alveolar lining cells. Conclusion. We encountered an extremely rare case of papillary adenoma of the lung, which is a benign epithelial tumor of the respiratory tract.