Ch04: Chest Radiology — Specific Disorders（胸部疾病影像诊断）

# Ch04: Chest Radiology — Specific Disorders（胸部疾病影像诊断）

Preparatory Mindset

This chapter covers the specific chest disorders from the teacher's Part III lecture: pneumonia (bacterial, viral/mycoplasma, fungal, immunocompromised), lung abscess, pulmonary tuberculosis, sarcoidosis, diffuse interstitial fibrosis, radiation pneumonitis, collagen vascular diseases, pneumoconiosis (coal workers', asbestos), and airway diseases (COPD/emphysema, bronchiectasis). The major purpose of CXR in suspected chest infection is to establish whether pneumonia is present — identifying the responsible organism radiologically is rarely possible because appearances overlap.

Core Concepts

Bacterial pneumonia

• One or more areas of consolidation, from a small ill-defined opacity to a whole lobe.
• Cavitation may occur within consolidated areas.
• DDx: pulmonary edema, pulmonary infarction.
• Common CAP lobar pneumonia organism: Streptococcus pneumoniae.
• Lung abscess (complication): localized suppurative lesion; spherical opacity with central lucency ± air-fluid level; smooth inner wall, even wall thickness. Difficult to distinguish from cavitating neoplasm or Wegener's granulomatosis.

Viral and mycoplasma pneumonia

• Loss of clarity of vascular markings; widespread or localized ill-defined patchy consolidation.
• Pleural effusions are rare.
• The radiological abnormality may persist for many weeks after clinical recovery.

Pulmonary tuberculosis

• Primary TB (first infection, usually childhood): Ghon focus = area of consolidation, usually mid/upper zones; primary complex = small pulmonary opacity (sometimes invisible) + enlarged hilar/mediastinal lymph nodes. Heals and often calcifies (calcified primary complex remains visible for life).
• Spread: bronchial tree → tuberculous bronchopneumonia (patchy/lobar, often multi-lobar, bilateral, frequently cavitates); bloodstream → miliary TB (innumerable small nodules, uniform in size/density/distribution).
• Secondary (reactivation) TB: cough, hemoptysis, weight loss, night sweats, malaise. Location: apical and posterior segments of upper lobes; apical segments of lower lobes. Ill-defined consolidations; cavitation common.
• Progression: consolidation → cavitation → fibrosis ± calcification; pleural effusions leave permanent thickening/calcification.
• Is TB active? Active: ill-defined opacities, cavitation, new lesions on serial films, positive sputum. Stable/inactive: well-defined opacities, more calcification, lack of change over time.
• Key signs: cavity with smooth inner wall, spherical opacities, tree-in-bud sign.

Fungal pneumonia

• Normal host (histoplasmosis, coccidioidomycosis, blastomycosis): similar to TB, cavitation a particular feature; healing by fibrosis and calcification.
• Aspergillosis (Aspergillus fumigatus) three ways: ① colonize a pre-existing cavity → fungus ball/mycetoma; ② pneumonia in the immunocompromised; ③ allergic bronchopulmonary aspergillosis.

Pneumonia in the immunocompromised host

• More susceptible to infection; atypical radiographic appearance; usually widespread non-specific opacification (may be indistinguishable from edema, hemorrhage or neoplastic disease).
• Opportunistic fungi, TB, Pneumocystis jirovecii (in AIDS: widespread low-density air-space opacity, ground-glass opacification, reticular opacities/septal thickening).

Sarcoidosis

• Non-caseating granulomas in many organs; diagnosis by correlating clinical, pathological and radiological features.
• Chest findings: bilateral and symmetrical hilar and paratracheal lymphadenopathy; reticulonodular opacities maximal in mid and upper zones → pulmonary fibrosis (irreversible). ~10% develop significant lung involvement.

Diffuse interstitial pulmonary fibrosis

• Known causes: extrinsic allergic alveolitis, collagen vascular diseases (notably rheumatoid arthritis), drug-induced fibrosis, pneumoconiosis, sarcoidosis, idiopathic (UIP/IPF/cryptogenic fibrosing alveolitis).
• UIP: thickening of alveolar walls with fibrosis; progression → breakdown of alveolar walls → small rounded air-spaces → 'honeycomb lung' (restrictive defect, severe reduction in gas transfer). Imaging: hazy basal opacities → loss of vessel clarity → honeycombing (ill-defined nodules with connecting lines & circular lucencies, subpleural, basal predominance) → pulmonary hypertension → cardiomegaly. Higher incidence of lung cancer in these patients.

Radiation pneumonitis

• After radiotherapy for intrathoracic neoplasms and breast carcinoma.
• Initially no change → a few weeks later ill-defined small opacities in the radiation field → fibrosis with dense coarse opacification.

Collagen vascular diseases

• Wegener's granulomatosis: one or more well-defined consolidations/masses, usually mid zones, which may cavitate; difficult to distinguish from bronchogenic carcinoma (single) or metastases (multiple).

Pneumoconiosis

• Coal workers' pneumoconiosis: many small nodules similar to miliary TB → progressive massive fibrosis (homogeneous rounded opacities in the upper halves of the lungs).
• Asbestos-related disease: ① pleural plaques (minor exposure) — localized, some calcified, harmless, indicate prior exposure; ② diffuse pleural thickening (may encase lungs → restrictive); ③ asbestosis — bilateral, maximal at bases; ④ malignant mesothelioma and bronchial carcinoma at far higher frequency.

Airway diseases

• Chronic bronchitis = clinical diagnosis (productive cough ≥3 consecutive months in 2 successive years); CXR usually normal; if abnormal → complication (emphysema, pneumonia, cor pulmonale).
• Emphysema = increase beyond normal size of air-spaces distal to the terminal bronchiole with destructive wall changes. Imaging: increased lung volume (low flat diaphragm — midpoints below 7th rib anteriorly/12th rib posteriorly; elongated narrow heart; wide intercostal spaces); attenuated vessels (reduced size/number; bulla = sharply demarcated focal region).
• Bronchiectasis = irreversible dilatation of bronchi, often with impaired drainage → persistent infection. HRCT diagnostic: signet ring sign; CXR: tram-track opacities. Causes: recurrent infection, cystic fibrosis, ciliary dyskinesia.

High-Yield Points

• Key Point: Bacterial pneumonia = consolidation + air bronchogram; viral/mycoplasma = patchy, ill-defined, no effusion.
• Key Point: Primary TB = Ghon complex (Ghon focus + hilar nodes); secondary TB = upper lobe apical/posterior cavitary disease; miliary = uniform small nodules.
• Key Point: Active TB = ill-defined opacities + cavitation + new lesions; healing = calcification + well-defined margins.
• Key Point: Sarcoidosis = bilateral symmetrical hilar adenopathy + mid/upper zone reticulonodular opacities.
• Key Point: UIP/IPF = subpleural basal honeycombing.
• Key Point: Emphysema = hyperinflation (low flat diaphragm, wide rib spaces) + attenuated vessels + bullae.
• Key Point: Asbestos → pleural plaques (benign) but also mesothelioma and bronchial carcinoma.
• Key Point: Bronchiectasis = signet ring sign on HRCT.

Topic Summary

Specific chest disorders cluster into infections (bacterial/viral/mycoplasma/fungal/TB/immunocompromised), granulomatous disease (sarcoidosis), interstitial disease (UIP/IPF, radiation, collagen vascular), occupational disease (coal, asbestos) and airway disease (COPD/emphysema, bronchiectasis). Master the classic signatures: lobar consolidation + air bronchogram (S. pneumoniae), upper-lobe cavitary disease + tree-in-bud (reactivation TB), bilateral hilar adenopathy (sarcoidosis), subpleural honeycombing (UIP), hyperinflation + bullae (emphysema), signet ring sign (bronchiectasis).

Illustrations（图解速览）

Case gallery for this chapter — identify the imaging technique, location, features and diagnosis for each: