From the Guidelines
Mosaic attenuation on a CT scan is defined as a sharply defined geographic patchwork of regions of differing attenuation on full inspiratory images, representing heterogeneous air trapping in the lungs. This imaging finding is crucial for accurate diagnosis and appropriate management of underlying respiratory conditions, such as small airway diseases like bronchiolitis, asthma, and bronchiectasis, as well as vascular diseases like pulmonary embolism or pulmonary hypertension 1.
Key Characteristics of Mosaic Attenuation
- Mosaic attenuation is characterized by a patchwork appearance with areas of both increased and decreased density throughout the lung tissue.
- It represents heterogeneous air trapping in the lungs, where some areas have reduced air flow while others maintain normal ventilation.
- The term mosaic attenuation is reserved for findings on inspiratory CT imaging 1.
Distinguishing Between Airway and Vascular Causes
- When interpreting mosaic attenuation, it's essential to determine whether the darker areas (lower density) or the lighter areas (higher density) represent the abnormal lung tissue.
- In airway diseases, the darker areas are abnormal due to air trapping, while in vascular diseases, the lighter areas indicate reduced perfusion.
Importance of Expiratory CT Scans
- Expiratory CT scans can enhance the contrast between normal and abnormal lung regions, making it easier to visualize mosaic attenuation.
- This pattern is best visualized on expiratory CT scans, which can help distinguish between airway and vascular causes of mosaic attenuation 1.
Clinical Significance
- Recognizing mosaic attenuation is crucial for accurate diagnosis and appropriate management of underlying respiratory conditions.
- Mosaic attenuation can be associated with various diseases, including hypersensitivity pneumonitis, pulmonary hypertension, and chronic pulmonary embolism 1.
From the Research
Definition of Mosaic Attenuation
Mosaic attenuation on a computed tomography (CT) scan refers to heterogeneous areas of differing lung attenuation, resulting from diverse causes including diseases of the small airways, pulmonary vasculature, alveoli, and interstitium, alone or in combination 2, 3.
Causes of Mosaic Attenuation
The causes of mosaic attenuation can be categorized into:
- Small-airway disease, such as respiratory bronchiolitis or constrictive bronchiolitis 3
- Vascular lung disease, including chronic thromboembolic pulmonary hypertension and pulmonary arterial hypertension 3, 4
- Infiltrative disease, which can result in a mosaic pattern related to various processes in acute, subacute, or chronic settings 3, 5
Differentiation of Causes
Imaging clues that can assist in pinpointing a diagnosis include:
- Evidence of large airway involvement
- Cardiovascular abnormalities
- Septal thickening
- Signs of fibrosis
- Demonstration of airtrapping at expiratory imaging 3
- The size of pulmonary vessels within the lucent regions of lung, which can be small relative to the vessels in the more opaque lung in small airways disease and pulmonary vascular disease 4
Diagnostic Challenges
While it is sometimes possible to distinguish among the categories of disease causing mosaic attenuation, vascular disease is often misinterpreted as infiltrative lung disease or airway disease 5. The use of paired inspiratory/expiratory CT scans can help distinguish small airways disease from primary vascular disease 4.