Rhabdomyomatous dysplasia of the lung

This article deals with the presence of nontumoral striated muscle fibers in the lungs of 3 neonates. These cells were diffusely distributed in one lung (case 1) or in both (case 2), or focally localized to the lung parenchyma adjacent to the liver in a case with a large right diaphragmatic hernia (case 3). The striated muscle fibers were located in the walls of small bronchi and bronchioli or in the alveolar interstitium. Other major lung malformations found simultaneously were absence of lobation, hypoplastic lungs, and hypoplastic pulmonary vessels. The origin of striated muscle fibers in the neonatal lung has been attributed to anomalous differentiation of mesoblastic cells (as in cases 1 and 2). The presence of striated muscle cells in the lower margin of a hypoplastic lung associated with a right diaphragmatic hernia (case 3) suggests that intrapulmonary inclusion of diaphragmatic muscle fibers might be a source as well. Striated muscle fibers in the lung are commonly associated with major malformations involving heart and lungs, suggesting a much wider morphogenetic error.