Main aetiologies to be considered in cases of chronic single or multiple alveolar opacities
| Frequent causes |
| Bacterial or viral pneumonia, slow to resolve |
| Organising pneumonia |
| Tuberculosis |
| Pulmonary infarction |
| Less frequent causes |
| Lepidic adenocarcinoma |
| Pseudo-alveolar sarcoidosis |
| Lymphoma |
| Bacterial pneumonia involving slow-growing organisms (nocardiosis, actinomycosis) |