An unusual case of pulmonary hamartoma with predominant bronchial mucous glands in the peripheral lung

Pulmonary hamartoma (PH) is the most common benign lung tumor, comprising various amounts of mescenchymal components with entrapped epithelial components. We describe an unusual case of PH in the left lower lung lobe of a 60-year-old female. The tumor was 9x9mm in size, light brown, weakly glistening, and microscopically found to be composed of well-developed epithelial and mesenchymal components without atypia. Both components were intermingled but without apparent transition. Epithelial components were occupied by predominant bronchial mucous glands. Serous glands, entrapped bronchioles, and clefts lined by respiratory epithelium were also apparent. Mesenchymal components including cartilage and fat were scattered, and swirling smooth muscle fascicles were interlaced with epithelial components. Collision tumor or other biphasic tumors were unlikely, and hyperplastic change in bronchial glands as in the rare conditions of intraoral minor salivary glands and epithelial entrapments by PH may explain these interesting histological findings. It is important to be aware of the possibility that a large number of bronchial mucous glands may be noted in the peripheral lung, and not to mistake this for other malignancies.