Mesenchymal Cystic Hamartoma of the Lung

Mesenchymal hamartomatous nodules and cysts in the lungs caused hemoptysis, pneumothorax, hemothorax, pleuritic chest pain, dyspnea of slight or moderate degree, or a combination of these signs and symptoms in five patients. In four cases the disease was multifocal and bilateral. The nodules were composed of primitive mesenchymal cells subdivided into papillae by a plexus of small airways lined with respiratory epithelium. The nodules grew slowly in number and size over the years and apparently became cystic when they reached a diameter of about 1 cm. The cysts had a cambium layer of mesenchymal cells and were lined with normal or metaplastic respiratory epithelium. In general, the disease had an indolent course. The most serious complications were sudden hemorrhage into a cyst from large systemic arteries supplying the walls of the cysts, pneumothorax or hemothorax from rupture of a subpleural cyst, and malignant transformation in one case. This disease appears to represent a distinct clinicopathological entity, which I term mesenchymal cystic hamartoma of the lung. (N Engl J Med 1986; 315:1255–9.) THE nature of a cyst detected on a chest radiograph can rarely be defined before excision if there is no known underlying lung disease. Surgical extirpation may be indicated to prevent hemorrhage, infection, or pneumothorax, or to exclude neoplasm if the cyst has a solid wall. I describe here five patients who had nodules or cysts in the lungs and an indolent clinical course. Some characteristics of two of the five patients have been described in previously published case reports. 1 , 2 The nodules and cysts proved to be hamartomas with both mesenchymal and epithelial elements. I believe that these patients have . . .