From the Guidelines
Mosaic lung attenuation is indicative of small airways disease, most commonly seen in conditions like bronchiolitis obliterans, asthma, and hypersensitivity pneumonitis, as it reflects regional differences in lung perfusion and air trapping. This radiological pattern appears on CT scans as a patchwork of areas with different densities throughout the lung fields, creating a mosaic-like appearance. The pattern develops due to regional differences in lung perfusion and air trapping, as described in the American Journal of Respiratory and Critical Care Medicine 1. In affected areas, narrowed or obstructed small airways prevent normal air outflow during expiration, leading to air trapping and appearing as areas of decreased attenuation (darker regions) on CT. Meanwhile, adjacent normal lung tissue may show increased attenuation (lighter areas) due to compensatory increased blood flow.
Some key points to consider when interpreting mosaic lung attenuation include:
- It can be seen in both inspiratory and expiratory CT scans, but becomes more pronounced on expiratory scans 1
- The presence of a "three-density pattern" (a combination of lung lobules with preserved density, surrounded by patchy or lobular ground-glass attenuation, and interspersed with lobules of decreased density and decreased vessel size) is highly specific for hypersensitivity pneumonitis 1
- Mosaic attenuation can occasionally be seen in pulmonary vascular diseases like chronic thromboembolic pulmonary hypertension, where the primary mechanism is regional differences in perfusion rather than ventilation
- The diagnosis of fibrotic hypersensitivity pneumonitis can be suggested by the presence of coexisting lung fibrosis and signs of bronchiolar obstruction, including mosaic attenuation and air trapping 1
Overall, mosaic lung attenuation is an important radiological feature that can help diagnose and manage various lung conditions, particularly small airways disease and hypersensitivity pneumonitis.
From the Research
Mosaic Lung Attenuation
Mosaic lung attenuation is a nonspecific finding that can reflect the presence of various diseases, including:
- Vascular disease
- Airway abnormalities
- Ground-glass interstitial or air-space infiltrates
- Small airways disease
- Infiltrative lung disease
Causes of Mosaic Attenuation
The causes of mosaic attenuation can be differentiated into several categories, including:
- Infiltrative lung disease, such as ground-glass opacity 2, 3, 4, 5
- Airway disease, such as small airways disease, constrictive bronchiolitis, and respiratory bronchiolitis 2, 3, 4, 6, 5
- Vascular disease, such as chronic thromboembolic pulmonary hypertension and pulmonary arterial hypertension 2, 3, 4, 5
Differentiation of Mosaic Attenuation
The differentiation of mosaic attenuation can be achieved through:
- Paired inspiratory/expiratory CT scans 2, 6
- Assessment of pulmonary vessels within the lucent regions of lung 2
- Evaluation of ancillary CT findings, such as evidence of large airway involvement, cardiovascular abnormalities, septal thickening, and signs of fibrosis 4, 5
- Clinical history and correlation with clinical and physiological variables, such as spirometry parameters and impulse oscillometry indices 6