Pulmonary Alveolar Proteinosis – Differential Diagnosis of Crazy Paving Pattern

History: 50 year old male with diabetes, hypertension, obstructive sleep apnea, and hyperlipidemia presents with 1 week history of hemoptysis.

Pulmonary alveolar proteinosis: Single axial CT scan of chest in lung windows shows bilateral ground glass opacities with interlobular septal thickening consistent with so called “crazy paving” pattern. Note the peripheral lung is spared. The main pulmonary artery is dilated, concerning for pulmonary arterial hypertension.

The differential for crazy paving pattern is wide, however, classically it is seen with pulmonary alveolar proteinosis, which was the diagnosis in this case.

The differential diagnosis for crazy paving pattern is as follows:

1. Pulmonary alveolar proteinosis

2. Pneumocystis pneumonia

3. Acute interstitial pneumonia

4. Diffuse alveolar damage or hemorrhage

5. Pulmonary edema

6. Nonspecific interstitial pneumonia

7. Eosinophilic pneumonia

8. Cryptogenic organizing pneumonia

There are other more rare entities that can manifest as a crazy paving pattern.