Pulmonary alveolar proteinosis (PAP) is caused by alveoli and bronchiolar lumens filled with insoluble phospholipid-rich protein substances. PAP can be congenital or secondary to malignant tumors or immunodeficiency.
Clinical presentation and pathology
PAP is common in young and middle-aged males. The onset is often insidious. The symptoms are tachypnea on exertion in the early stage, gradually progress to tachypnea at rest, and white or yellow expectoration. The systemic symptoms are inapparent. When secondary lung infection occurs, corresponding symptoms and signs occur. Respiratory failure may occur in severe patients.
Pathologically, there is mostly consolidation, yellow or yellowish grey nodule can be seen under the pleura, and yellow fluid exudates on the section. After bronchoalveolar lavage, microscopy shows that the alveoli and bronchioles are filled with phospholipid-rich protein substances, and eosinophilic staining is positive.
Imaging manifestations
X-ray
On chest plain film, initial diffuse ground-glass opacities in both lungs are followed by patchy opacities and fused consolidation, and air bronchogram sign is often seen. The lesions in the lungs are inhomogeneously distributed, usually more apparent near the hilum, and show butterfly opacities, resembling the manifestations of cardiogenic or uremic pulmonary edema.
CT
On thin-section high-resolution CT, the boundaries between the lesions and the peripheral normal tissues are clear, and there are geographic opacities. The interlobular septa are irregularly thickened and polygonal, and overlap with the ground-glass opacity, forming crazy paving pattern.
Figure 1 Pulmonary alveolar proteinosis
CT lung window shows diffuse ground-glass opacities in both lungs with geographic distribution, thickened interlobular septa overlapped with the ground-glass opacities forming crazy paving pattern.
Diagnosis and differential diagnosis
The imaging manifestations of this disease have certain characteristics, but similar manifestations can also be seen in other diseases, such as exogenous lipoid pneumonia. Therefore, a comprehensive consideration of clinical presentation, imaging manifestation, and bronchoalveolar lavage is needed. Transbronchial lung biopsy can be considered for definite diagnosis.