This study pertains to an entity characterized by the presence of multiple intrapulmonary nodules, which consist of an admixture of bundles of well-differentiated smooth muscle cells and epithelial-lined spaces. These lesions have been frequently interpreted as a variant of hamartomas. However, in this review of the literature, and careful analysis of nine cases of this entity, we concluded that they should be considered metastases from smooth muscle tumors which incorporate some structures of mature lung parenchyma as they slowly expand. We affirm that the designation “fibroleiomyomatous hamartoma” should be discarded.
Our cases occurred in six female and three male patients. In all but one female the primary source for lung metastases was uterus, while the male patients had primary lesions in the saphenous vein, diaphragm, and soft tissues. These lung lesions increase in size and number and are potentially fatal, though this may take many years. Even though the smooth muscle cells of the lung nodules appear bland on light microscopy, we were always able to demonstrate mitotic activity; electron microscopy indicated immaturity of the cells.
For these reasons, we believe the tumors to represent metastatic leiomyosarcomas.