Histopathological evaluation of a specimen from open lung biopsy out of the right lung showed amorphous eosinophilic material in the alveoli, positive on periodic acid Schiff (PAS) staining. This eosinophilic material corresponded with deficient surfactant (Fig. 2c) . The lines visible on CT corresponded to deposition of material within the airspaces at the borders of the acini in the secondary pulmonary lobules (periacinar pattern; Fig. 2b ). The diagnosis of alveolar proteinosis was made.