From the Guidelines
Mosaic attenuation on CT chest is a significant finding that requires thorough evaluation to determine the underlying cause, which can be small airways disease, pulmonary vascular disease, or infiltrative lung disease, and management should be tailored accordingly to improve morbidity, mortality, and quality of life. The clinical significance of mosaic attenuation varies widely, and it can represent a benign finding or indicate serious conditions like pulmonary hypertension 1. Initial evaluation should include pulmonary function tests, particularly with air trapping assessment, and detailed clinical history focusing on exposures and symptoms.
Causes of Mosaic Attenuation
- Small airways disease, such as asthma or bronchiolitis, is the most common cause of mosaic attenuation, and treatment includes bronchodilators, inhaled corticosteroids, and removing triggering agents 1.
- Pulmonary vascular causes, like chronic thromboembolic pulmonary hypertension, may require anticoagulation, pulmonary vasodilators, or surgical intervention 1.
- Infiltrative causes, such as hypersensitivity pneumonitis, need antigen avoidance and sometimes immunosuppression 1.
Diagnostic Approach
- Expiratory CT images are particularly valuable as they enhance visualization of air trapping in small airways disease 1.
- A diagnostic predictive model that includes patient age, a history of down feather and/or bird exposure, the presence of diffuse craniocaudal GGO, and mosaic perfusion on HRCT imaging can help diagnose chronic hypersensitivity pneumonitis with a specificity of 91% and sensitivity of 48% 1.
- The three-density sign, which is a combination of areas of decreased attenuation, normal lung, and areas of increased ground-glass lung opacification on HRCT imaging, is highly specific for distinguishing fibrotic hypersensitivity pneumonitis from idiopathic pulmonary fibrosis, with a specificity of 93% and sensitivity of 49% 1.
Management and Follow-up
- Management should be tailored to the underlying cause of mosaic attenuation, and follow-up imaging is recommended to monitor disease progression and treatment response, with intervals determined by the specific diagnosis and clinical stability 1.
- The goal of management is to improve morbidity, mortality, and quality of life, and a thorough evaluation and tailored treatment approach are essential to achieve this goal.
From the Research
Clinical Significance of Mosaic Attenuation on CT Chest
- Mosaic attenuation on computed tomography (CT) chest refers to a pattern of variable lung attenuation that can be seen in various diseases, including chronic thromboembolic pulmonary hypertension (CTEPH) 2, small-airway disease, vascular lung disease, and infiltrative disease 3.
- This pattern presents a challenge to radiologists in determining which regions of the lung are abnormal, as both areas of low and high attenuation can be seen 3.
- The mosaic pattern can be a sign of variable regional perfusion and may suggest chronic pulmonary thromboembolism as a cause for pulmonary hypertension 4.
Management of Mosaic Attenuation on CT Chest
- The management of mosaic attenuation on CT chest depends on the underlying cause of the pattern.
- In patients with CTEPH, the mosaic attenuation pattern can be used to assess pulmonary perfusion and guide treatment decisions 2.
- In other cases, additional imaging findings and clinical information may be needed to distinguish among different causes of the mosaic pattern, such as infiltrative lung disease, airway disease, and vascular disease 3, 5, 6.
- Thin-section CT scans can be used to differentiate among these causes, with infiltrative lung disease and airway disease being more reliably diagnosed than vascular disease 6.
Differential Diagnosis of Mosaic Attenuation on CT Chest
- The differential diagnosis of mosaic attenuation on CT chest includes:
- Chronic thromboembolic pulmonary hypertension (CTEPH) 2, 4
- Small-airway disease 3
- Vascular lung disease 3, 5
- Infiltrative lung disease 3, 6
- Airway disease 3, 6
- The frequency of the mosaic pattern varies among these causes, with vascular disease being more commonly associated with the pattern than cardiac or lung disease 5.