Airspace opacities: Ground-glass opacity to dense consolidation

Reactive lymphadenopathy; very large lymph nodes unusual

Parapneumonic pleural effusion or empyema

Correlation with sputum, WBC count, and clinical presentation paramount

Consider fungal agents and PCP in the correct clinical setting

Consolidation in gravity-dependent portions of lungs

Predisposed patients (alcoholism, epilepsy, hiatal hernia, esophageal dysmotility or obstruction, neuromuscular disorders)

Supine: Superior segments of lower lobes and posterior segments of upper lobes

Upright: Basilar segments of lower lobes

Centrilobular or tree in bud opacities common on CT

May progress to necrotizing pneumonia or pulmonary abscess without treatment

Gas-filled cavity arising from focal pneumonia (usually due to aspiration)

Abscess 1-2 weeks after development of pneumonia

Gas-fluid level or smaller foci of gas

Empyema and bronchopleural fistula

May be difficult to differentiate from empyema

Discoid or plate-shaped

Usually in dependent aspects of lower lobes or in basilar aspects of right middle lobe or lingula

Crosses pulmonary segments

Often touches visceral pleura

Most common in upper lung zone (2/3 of primary lung cancers)

Spiculated or irregular margins; pleural tail

Thick-walled or nodular cavitation

Large hilar &/or mediastinal lymphadenopathy (> 2 cm)

Concomitant emphysema and smoking history

Variable-sized, well-marginated pulmonary nodules preferentially in peripheral and lower lungs

Feeding artery sign: Pulmonary artery branches extend to nodules, implying hematogenous spread

Solitary metastasis: Renal cell carcinoma, colon cancer, breast cancer, sarcomas, melanoma

Ground-glass opacities > consolidation; may be diffuse, patchy, lobular, or centrilobular

Increased interlobular and intralobular septal thickening over 1-2 days

Rapid resolution in days; not as rapid as in cardiogenic pulmonary edema or bland aspiration

Pulmonary opacities corresponding to radiation ports

Pulmonary ground-glass opacities and consolidation (radiation pneumonitis) appears 6-8 weeks after initial treatment

Radiation pneumonitis peaks 3 months after end of treatment

Evolution of pulmonary opacities into lung fibrosis from 3-18 months after end of treatment

From 18 months after end of treatment and onward lung fibrosis stable

Nodules from silicosis or coal worker’s pneumoconiosis coalesce into biapical mass-like consolidation, ± cavitation

Lateral margin parallels chest wall, sharply defined

Hilar and mediastinal lymphadenopathy, ± eggshell calcification

Perilymphatic nodules with symmetric mediastinal and hilar lymphadenopathy

Small nodules may coalesce into focal opacity (alveolar sarcoidosis)

Tiny nodules around a larger dominant nodule (galaxy sign)

Interlobular septal thickening

Lower lung predominant, peripheral/subpleural, wedge-shaped consolidation

In setting of acute pulmonary arterial thromboembolism

Reverse halo configuration (central ground-glass opacity and peripheral rim of consolidation)

Often in setting of superimposed cardiac dysfunction (cardiomyopathy, congestive heart failure)

Single or multiple nodules with feeding artery and vein

Lower and medial lungs

History of hereditary hemorrhagic telangiectasia

Multiple ill-defined nodules that may cavitate

May occur in association with nodal disease or primarily in lungs

Exogenous aspiration of fatty material

Nodular or mass-like consolidation often with fatty CT attenuation

Fat density may not be evident because of inflammation and scarring

Irregular margins, may mimic bronchogenic carcinoma

Gravity-dependent portions of lungs