The differential diagnosis for<unk> es is broad. General etiologies include infections, interstitial lung diseases, pulmonary edema, pulmonary hemorrhage, and neoplasm. A correlation of imaging with a patient's clinical features is useful in narrowing the diagnosis.<unk> s can be seen in normal lungs. Upon expiration there is less air in the lungs, leading to a relative increase in density of the tissue, and thus increased attenuation on CT. Furthermore, when a patient lays supine for a CT scan, the posterior lungs are in a dependent position, causing partial collapse of the posterior alveoli. This leads to an increase in density of the tissue, resulting increased attenuation and a possible<unk><unk>  appearance on CT. Infectious causes In the setting of pneumonia, the presence of<unk>  (as opposed to consolidation) is a useful diagnostic clue. Most bacterial infections lead to lobar consolidation, while atypical pneumonias may cause<unk> s. It is important to note that while many of the pulmonary infections listed below may lead to<unk> s, this does not occur in every case. High-Resolution CT image in a patient with Pneumocystis pneumonia infection showing<unk> es. Bacterial * Diffuse * Mycoplasma pneumoniae * Chlamydophila pneumoniae * Legionella pneumophilia * Focal or nodular * Mycobacterium * Nocardia * Septic emboli Viral * Adenovirus * Coronavirus (including MERS-CoV, SARS-CoV, and SARS-CoV-2) * Cytomegalovirus (CMV) * Herpes Simplex Virus (HSV) * Human metapneumovirus (HMPV) * InfluenzaCT image showing<unk><unk>  opacification in the posterior of the right lung (screen left). * Measles *Respiratory Syncytial Virus (RSV) * Varicella zoster Fungal * Pneumocystis jirovecii (PCP) * Invasive aspergillosis * Candidiasis * Mucormycosis *Pulmonary cryptococcus *Paracoccidioidomycosis Parasitic * Pulmonary Schistosomiasis Non-infectious causes CT image showing patchy areas of<unk> es representing pulmonary edema. Exposures * Aspiration pneumonitis *Drug toxicity (most common include cyclophosphamide, amiodarone, carmustine, methotrexate, and bleomycin) *Hypersensitivity pneumonitis *EVALI *Radiation pneumonitis Idiopathic interstitial pneumonia * Acute interstitial pneumonitis * Desquamative interstitial pneumonia * Lymphocytic interstitial pneumonia * Non-specific interstitial pneumonia * Cryptogenic organizing pneumonia Neoplastic processes * CT image showing diffuse<unk> s throughout both lungs. An abscess is also noted in the right lung (screen left).Lung adenocarcinoma * Adenocarcinoma in situ of the lung * Atypical adenomatous hyperplasia Additional causes * Acute eosinophilic pneumonia *Cholesterol granulomas *Focal interstitial fibrosis *Granulomatosis with polyangiitis *Lymphatoid granulomatosis * Pulmonary alveolar proteinosis *Pulmonary calcifications *Pulmonary capillary hemangiomatosis *Pulmonary contusion *Pulmonary edema *Pulmonary hemorrhage *Pulmonary infarction *Sarcoidosis *Thoracic endometriosis
Ground-glass opacity
Colloid nodule
Companion shadow
Pleural thickening
Subcutaneous emphysema
Tracheobronchomegaly
Pulmonary consolidation
Peribronchial cuffing