From the Guidelines
Common CT chest findings in patients with Mycobacterium avium complex (MAC) include bronchiectasis, small nodules (<10 mm), tree-in-bud opacities, and consolidation, which are typically distributed in the middle lobe and lingula in nodular bronchiectatic MAC, while fibrocavitary MAC often shows upper lobe cavitary lesions resembling tuberculosis. These findings are based on the most recent and highest quality study available, which provides a comprehensive overview of the radiographic features of MAC lung disease 1.
Key Radiographic Features
- Bronchiectasis: appears as bronchial dilation with thickened walls, often with a "signet ring" appearance when viewed in cross-section
- Small nodules: frequently centrilobular and may connect to linear branching opacities creating the tree-in-bud pattern, which represents inflammation in small airways filled with mucus and infectious material
- Tree-in-bud opacities: represent inflammation in small airways filled with mucus and infectious material
- Consolidation: areas may develop in more advanced disease
- Mosaic attenuation patterns: reflect air-trapping from small airway disease and are also common
Distribution Patterns
- Nodular bronchiectatic MAC: typically distributed in the middle lobe and lingula
- Fibrocavitary MAC: often shows upper lobe cavitary lesions resembling tuberculosis
These radiographic findings reflect MAC's pathophysiology, as the organism colonizes damaged airways and causes progressive inflammation, leading to further airway destruction and the characteristic bronchiectasis-nodule complex. The distribution pattern helps distinguish MAC from other pulmonary infections and guides diagnostic and treatment approaches 1.
From the Research
CT Chest Findings in MAC Patients
The common CT chest findings in patients with Mycobacterium avium complex (MAC) include:
- Bronchiectasis (97%) 2
- Small nodules (89%) 2
- Parenchymal distortion (60%) 2
- Bronchial wall thickening (56%) 2
- Consolidation (50%) 2
- Cavity formation (49%) 2
- Atelectasis 3
- Emphysema 3
- Ground-glass opacity 3
- Linear opacities 3
- Mediastinal lymphadenopathy 3
- Pleural disease 3
- Mosaic pattern of reduced lung attenuation 4
Characteristic Features
Some characteristic features of MAC lung disease on CT scans are:
- Widely distributed bronchiectasis and small nodules and/or cavities with thin, smooth walls 2
- Overinflation on chest radiography 3
- Ill-defined nodules, bronchiectasis, predominant middle lobe and/or lingular abnormalities, with or without overinflation 3
- Pleural thickening is associated with a worse degree of improvement after therapy 5
Diagnostic Utility
CT scans can be useful in: