From the Guidelines
Hypersensitivity pneumonia (HP) typically exhibits a classic distribution on high-resolution computed tomography (HRCT) scans, characterized by upper lobe predominant ground-glass opacities, mosaic attenuation, and fibrosis 1.
Key Features
- The radiographic pattern often correlates with the severity of disease, with more extensive involvement seen in chronic and subacute forms 1.
- Mosaic attenuation and air-trapping are common features of HP, particularly in the fibrotic form 1.
- The three-density sign, characterized by a combination of ground-glass opacification, normal lung, and air-trapping, is highly specific for fibrotic HP 1.
Distribution and Patterns
- The distribution of fibrosis in HP can be random, mid lung zone-predominant, or relatively spared in the lower lung zones 1.
- Upper lobe predominance is a common feature of HP, particularly in the chronic form 1.
- The pattern of organizing pneumonia can be seen in HP, with consolidation in a peribronchovascular and/or peripheral distribution 1.
Diagnosis and Evaluation
- The diagnosis of HP should be based on a combination of clinical, radiological, and histopathological findings 1.
- HRCT scans are essential in the evaluation of HP, with features such as mosaic attenuation, air-trapping, and fibrosis being highly suggestive of the disease 1.
From the Research
Classic Distribution of Hypersensitivity Pneumonitis (HP)
The classic distribution of Hypersensitivity Pneumonitis (HP) is characterized by:
- A bronchiolocentric granulomatous lymphocytic alveolitis, which evolves to fibrosis in chronic advanced cases 2
- Ground-glass and poorly defined nodules, with patchy areas of air trapping, are seen in acute/subacute cases on high-resolution computed tomography (HRCT) scan 2, 3
- Reticular opacities, volume loss, and traction bronchiectasis superimposed on subacute changes are observed in chronic cases on HRCT scan 2
- Centrilobular nodules, multifocal ground glass opacities, and evidence of air trapping in the expiratory phase of respiration are highly suggestive of hypersensitivity pneumonitis 4
- Mosaic attenuation and ground-glass opacities are also common findings on HRCT scans 3, 5
Key Features of HP Distribution
Key features of the distribution of HP include:
- Upper lobe predominance in advanced disease 3
- Peripheral distribution in the axial plane and lower lung preponderance in fibrotic HP 5
- Axially and zonally diffuse distribution in non-fibrotic HP 5
- Presence of air trapping and mosaic attenuation on chest computed tomography, which predicts survival in chronic HP 5