Multiple pulmonary (hamartomatous?) leiomyomas. Light and electron microscopic study.

The light and electron microscopical features of the lung tumors in a case of multiple pulmonary leiomyomas are described. The differential diagnosis of leiomyomatous tumors of the lung is discussed. They have to be differentiated from lymphangio-leiomyomatosis of the lungs. In the literature, multiple pulmonary leiomyomas are generally considered to be metastases from low grade uterine leiomyosarcoma or to be hamartomatous lung tumors. This is suggested by the glandular structures both within the tumor and on the surface. However, our ultrastructural observations showed these epithelia to have features of granular pneumocytes (type II), in particular they contain lamellar bodies and possess microvilli on their surface. Their formation is considered to be a secondary reaction of alveolar lining cells to tumor growth. A possible origin of multiple pulmonary leiomyomas from the contractile system of the lung acini (contractile interstitial cells) is discussed.