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Mosaic attenuation is a patchwork pattern of heterogeneous lung attenuation on high-resolution CT (HRCT), where areas of differing densities coexist within the lung parenchyma. It reflects regional variations in ventilation and/or perfusion, not a single disease entity.

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Etiopathology

Mosaic attenuation can arise from three broad categories:

Category Etiology
Small airways disease Air-trapping / obstructive causes:
• Constrictive/obliterative bronchiolitis
• Hypersensitivity pneumonitis (chronic)
• Asthma, bronchiectasis
• Post-infective bronchiolitis (adenovirus, TB)
Vascular causes Regional hypoperfusion:
• Chronic thromboembolic pulmonary hypertension (CTEPH)
• Pulmonary arterial hypertension (PAH)
• Pulmonary vein atresia/stenosis
• Vasculitis
Parenchymal/infiltrative disease • Ground-glass opacities (GGO) due to interstitial lung disease (ILD)
• Pneumonias (PCP, viral), pulmonary edema
• Alveolitis

Radiology

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Differentiation requires careful correlation with expiratory HRCT and vessel size assessment to distinguish between airway, vascular, and parenchymal causes.

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Etiology Group Imaging Clues Expiratory CT Vessel Size Examples
Airways disease Patchy low attenuation, bronchial thickening Air-trapping persists Normal Bronchiolitis, HP, asthma
Vascular disease Geographic lucent areas, fewer/smaller vessels No air-trapping Smaller in lucent zones CTEPH, PAH, vein atresia
Parenchymal disease Ground-glass opacities intermixed with normal No air-trapping Equal ILD, pneumonia, edema

![Mosaic attenuation. Mosaic pattern in a patient affected by asthma. Lung parenchyma shows different attenuation areas, due to presence of pulmonary lobules with decreased density, caused by air-trapping. This appearance recalls a mosaic, as clearly evident in the embedded figure.

Chiarenza, A., Esposto Ultimo, L., Falsaperla, D. et al. Chest imaging using signs, symbols, and naturalistic images: a practical guide for radiologists and non-radiologists. Insights Imaging 10, 114 (2019). https://doi.org/10.1186/s13244-019-0789-4](attachment:b3911919-fcc9-4646-99a0-a87a4e2668a8:image.png)

Mosaic attenuation. Mosaic pattern in a patient affected by asthma. Lung parenchyma shows different attenuation areas, due to presence of pulmonary lobules with decreased density, caused by air-trapping. This appearance recalls a mosaic, as clearly evident in the embedded figure.

Chiarenza, A., Esposto Ultimo, L., Falsaperla, D. et al. Chest imaging using signs, symbols, and naturalistic images: a practical guide for radiologists and non-radiologists. Insights Imaging 10, 114 (2019). https://doi.org/10.1186/s13244-019-0789-4

Key distinguishing clue:

Clinical Correlation

Management