Langerhans cell histiocytosis (LCH) is a systemic disease associated with the proliferation and accumulation (usually in granulomas) of Langerhans cells in various tissues.

Infiltration of smooth muscle-like cells in lymph vessels as well as the lung (pleura, alveolar septa, bronchi, pulmonary vessels and lymphatics as well as lymph nodes, especially in posterior mediastinum and retroperitoneum). Focal emphysema can develop because of airway narrowing, and the thoracic duct may be obliterated. Pulmonary lymphangiomyomatosis may lead to multiple small cysts with a hamartomatous proliferation of smooth muscle in their walls.