| Cause | Examples |
| Infection | Bacteria e.g. Actinomyces spp., Nocardia spp., Mycobacterium spp.; Fungi e.g. Aspergillus spp., Cryptococcus spp., pneumocystosis; Parasites e.g. Echinococcus spp. |
| Pneumonia | |
| Lung abscess | |
| Septic (metastatic) embolism | |
| Autoimmune disease | Granulomatosis with polyangiitis |
| Sarcoidosis | |
| Rheumatoid arthritis | |
| Ankylosing spondylitis | |
| Systemic lupus erythematosus | |
| Malignancy | Primary lung cancer, mostly squamous cell |
| Lymphoma | |
| Lung metastasis | |
| Kaposi’s sarcoma | |
| Congenital abnormality/acquired lung disease | Bronchogenic cyst |
| Histiocytosis X (langerhans histiocytosis) | |
| Lymphangioleiomyomatosis | |
| Vascular disease | Pulmonary embolism (septic or aseptic) |
| BOOP/COP | Due to e.g. medication, radiotherapy or autoimmune disease |
Data from [6]. BOOP: bronchiolitis obliterans organising pneumonia; COP: cryptogenic organising pneumonitis.