RESUMEN
Mesenchymal cystic hamartoma of the lung is quite rare lesion which has an unknown prevalence, firstly described in 1986. It is characterized by multiple nodules and variable sized cysts in both lung field. The nodules of immature mesenchymal cells gradually enlarge and become cysts which are lined with normal or metaplastic respiratory epithelium and have the cambium layer of primitive mesenchymal cells. Main symptoms are hemoptysis, recurrent pneumothorax, and hemothorax. It is known to benign tumor, but has possibility of malignant degeneration. In gross findings in opertive field, multiple and variable-sized cystic lesions and nodules were observed. The cysts were lined with normal respiratory epithelium and had the cambium layer of primitive mesenchymal cell. Gross and microscopic findings were compatible with mesenchymal cystic hamartoma. We report a case of mesenchymal cystic hamartoma in a 27-year-old woman who had recurrent pneumothorax and hemoptysis.