Histopathology of pulmonary alveolar proteinosis

Open lung biopsy specimen shows that the alveolar septa are only slightly thickened due to type II epithelial cell hyperplasia, and the alveolar architecture is preserved. There is no inflammatory cell infiltration. The alveoli are filled with a flocculent and granular lipoproteinaceous material that stains pink with PAS stain.

Low-power photomicrograph of normal lung tissue shows open alveoli with thin, capillary-containing interstitial spaces. An artery (A) is identifiable by its thick, muscular wall; the accompanying bronchus (B) contains mucoid material and is lined by columnar respiratory epithelial cells.