| Bacterial | – Airspace consolidation (lobar or segmental) – Air bronchograms – Centrilobular nodules – Tree-in-bud opacities |
– Lung abscess – Cavitation (especially S. aureus, Klebsiella, Pseudomonas) – Pleural effusion or empyema – Bronchopneumonia pattern |
| Fungal | – Nodules with surrounding ground-glass halo (Halo sign, seen in invasive aspergillosis) – Consolidation (especially in immunocompromised patients) – Cavitation (aspergilloma, necrotizing fungal infection) |
– Air crescent sign (recovering invasive aspergillosis) – Peribronchovascular infiltrates – Miliary nodules (Histoplasmosis, Cryptococcus) – Lymphadenopathy (Histoplasmosis, Coccidioidomycosis) |
| Viral | – Ground-glass opacities (GGO) – Multifocal patchy consolidation – Peribronchial thickening |
– Interlobular septal thickening (e.g., COVID-19, CMV) – Crazy paving (e.g., COVID-19, SARS, MERS) – Nodules (rare in viral infections, but seen in measles pneumonia) |
| Atypical | – Ground-glass opacities – Tree-in-bud opacities – Peribronchovascular thickening (Mycoplasma, Chlamydia, Legionella) |
– Reticulonodular opacities (Mycoplasma pneumoniae) – Lower lobe predilection (Legionella) – Diffuse micronodules (Q fever, Psittacosis) |
| Parasitic | – Pulmonary nodules (Paragonimiasis, Echinococcus) – Cysts with air-fluid levels (Echinococcus) – Peribronchial inflammation (Strongyloides) |
– Miliary nodules (Toxoplasmosis, Disseminated Strongyloides) – Pleural effusion (Paragonimiasis) – Cavitation (*rare but possible in Paragonimiasis) |
Specific Pathogens in the Lungs
CT Appearances of Lung Infections by Organism
| Category | Organism | Acute CT Findings | Chronic CT Findings |
|---|---|---|---|
| Bacterial | Streptococcus pneumoniae | Lobar consolidation, air bronchograms | None (resolves with treatment) |
| Staphylococcus aureus | Patchy bronchopneumonia, cavitation (necrotizing pneumonia), pneumatoceles | Bronchiectasis (post-infectious sequelae) | |
| Klebsiella pneumoniae | Bulging fissure sign, extensive consolidation, cavitation | Chronic fibrosis, scarring | |
| Pseudomonas aeruginosa | Bronchopneumonia, tree-in-bud opacities, cavitation | Bronchiectasis, chronic scarring | |
| Legionella pneumophila | Multifocal consolidation, ground-glass opacities (GGO) | Mild residual fibrosis | |
| Fungal | Aspergillus (Invasive) | Halo sign (early), consolidation, nodules, cavitation | Air crescent sign (recovery), fibrosis |
| Aspergillus (Chronic Aspergillosis) | None | Cavitary lesions, aspergilloma (fungal ball), pleural thickening | |
| Histoplasma capsulatum | Patchy or miliary nodules, consolidation | Mediastinal/hilar lymphadenopathy, calcified nodules | |
| Cryptococcus neoformans | Nodules with GGO halo, consolidation | Fibrotic nodules, cavitary lesions | |
| Coccidioides immitis | Consolidation, nodules, pleural effusion | Cavitation, residual scarring | |
| Viral | Influenza | Diffuse GGO, multifocal consolidation | None (resolves in immunocompetent patients) |
| COVID-19 (SARS-CoV-2) | Bilateral peripheral GGO, crazy paving, consolidation | Fibrotic changes, traction bronchiectasis | |
| Cytomegalovirus (CMV) | Multifocal nodules, consolidation, interstitial thickening | Chronic nodules (rare) | |
| Measles (Morbillivirus) | Nodules, GGO, tree-in-bud opacities | Calcified nodules, bronchiectasis | |
| Atypical Bacteria | Mycoplasma pneumoniae | Ground-glass opacities, tree-in-bud opacities, peribronchial thickening | Reticulonodular opacities (rare) |
| Chlamydia pneumoniae | Reticulonodular infiltrates, patchy consolidation | None (typically resolves) | |
| Coxiella burnetii (Q Fever) | Ground-glass opacities, lobar or segmental consolidation | Chronic fibrosis, granulomas | |
| Parasitic | Paragonimus westermani | Cystic lesions, pleural effusion, nodules | Cavitary lesions, calcified nodules |
| Echinococcus granulosus (Hydatid disease) | Well-defined cysts, air-fluid levels, water-lily sign | Thick-walled cysts, fibrosis | |
| Strongyloides stercoralis | Diffuse GGO, peribronchial inflammation | Chronic fibrosis, nodular opacities | |
| Toxoplasma gondii | Diffuse micronodules (in immunocompromised hosts) | Chronic nodular opacities |