Mesenchymal cystic hamartoma of the lung.

Mesenchymal cystic hamartoma (MHC) of the lung is a very rare disease with an indolent clinical course and might be easily misdiagnosed as pleuropulmonary blastoma and other uncommon cystic lung lesions. We present a case of a 43-year-old woman who had sudden dyspnea resulting from a spontaneous right-sided pneumothorax. Computed tomography revealed multiple bilateral nodules and cysts of the right lung. Pathologically, the cysts and nodules were composed of primitive mesenchymal cells. The walls of the cysts were lined with normal respiratory epithelium and the nodules were permeated by scattered airways that were also lined with normal respiratory epithelium. Based on the combination of pathologic and clinical features, we made the diagnosis of MHC. One and one-half years after thoracotomy the patient is well without evidence of recurrence.