Pulmonary alveolar proteinosis (PAP)

HRCT of 30 year old female shows welldefined ground glass opacities which is associated with marked intelobular septal thickening and a sharp nonanatomic demarcation between normal and abnormal lung suggestive of "Crazy paving" pattern which is typical of PAP.

Pulmonary alveolar proteinosis (PAP) is a rare (1 case per 2 million), diffuse lung disease that is characterized by the alveolar and interstitial accumulation of a periodic acid-Schiff (PAS) stain-positive phospholipoprotein that is derived from surfactant.The lung architecture is otherwise normal, and any associated inflammation or fibrosis is limited in extent. Pulmonary alveolar proteinosis (PAP) occurs in primary and secondary forms. Primary PAP is either idiopathic (90% of cases) or congenital (2% of cases) in origin, whereas secondary PAP occurs in association with various pathologies like hematologic malignancies, particularly chronic myeloid leukemia and lymphomas, occupational exposures and associated with infections. Congenital PAP results from deficiency of surfactant protein B (SP-B) or abnormality of the granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor β chain.

CT scan with the above findings are almost diagnostic. razy paving is the characteristic finding of PAP on high-resolution CT (HRCT) scanning and consists of patchy, bilateral, geographic areas of ground-glass opacity that are associated with interlobular septal thickening. The disease is often distributed uniformly from the lung apex to the base. Interlobular septal thickening may be encountered more frequently in the lower lung zones.Classically, the abnormal pulmonary parenchyma is demarcated sharply from normal lung areas without a discernible anatomic boundary.

The crazy paving pattern also seen in many other condition like hydrostatic pulmonary edema, diffuse alveolar damage from any number of causes, pulmonary hemorrhage, diffuse pulmonary infections (including M tuberculosis, M pneumoniae, and other bacterial pneumonias), the diffuse form of bronchioloalveolar carcinoma, ARDS, drug-induced pneumonitis, radiation pneumonitis, bronchiolitis obliterans organizing pneumonia, chronic eosinophilic pneumonia, obstructive pneumonitis, acute interstitial pneumonia, and lipoid pneumonia.