Extranodal Rosai-Dorfman Disease : Lung
This is a case of Extranodal Rosai-Dorfman disease (RDD) involving lung. The pulmonary architecture is distorted by massive thickening of alveolar septa due to dense fibrosis, proliferation of S-100 positive histiocytes, and lymphoplasmacytic infiltrate. Involvement of lung in RDD is extremely rare. The list of entities in the differential diagnosis is long and includes: inflammatory myofibroblastic tumor, pulmonary hyalinizing granuloma, Langerhans' cell histiocytosis, Erdheim-Chester disease, infections (granulomatous, actinomycosis, botryomycosis), chronic aspiration, granular cell tumor, histiocytic malignancies, malakoplakia, focal eosinophilic pneumonia without eosinophils, histiocyte accumulation in areas of scarring, and pneumoconioses.