Migrating ground glass opacities on computed tomography due to gravitation in a patient with pulmonary alveolar proteinosis

An 80-year-old man presented with heterogeneous ground glass opacity, with interlobular septal thickening in the left lower lobe. The histology of a surgical lung biopsy showed alveolar proteinosis. Computed tomography revealed that the ground glass opacity and interlobular septal thickening observed dorsally in the supine position migrated to the ventral side in the prone position. To the best of our knowledge, this is the first report of a posture-dependent migrating shadow in a patient with pulmonary alveolar proteinosis.