Chat history
You said:
ChatGPT said:
Excellent question — yes, emphysema is a form of air trapping, but with a very specific mechanism.
In emphysema, destruction of alveolar walls and loss of elastic recoil prevent complete exhalation, so air becomes trapped in distal airspaces. This leads to hyperinflation and air trapping visible on imaging (especially on expiratory CT).
However, emphysema is only one of several entities that cause air trapping — some due to airway obstruction, others to structural or inflammatory changes. Below is a comprehensive table organizing the entities in the lungs associated with air trapping, grouped by pathophysiologic category.
Table: Entities in the Lungs Associated with Air Trapping
| Category | Entity | Definition / Mechanism | Imaging Features (CT or CXR) |
|---|---|---|---|
| Obstructive (Small Airway) | Asthma | Reversible bronchial smooth muscle constriction causing airflow limitation and incomplete emptying during expiration. | Patchy mosaic attenuation on expiratory CT; hyperlucent areas with air trapping. |
| Bronchiolitis Obliterans (Constrictive Bronchiolitis) | Inflammatory/fibrotic narrowing of small airways leading to air trapping. Often post-infectious or post-transplant. | Mosaic attenuation and air trapping on expiratory CT; normal or mildly abnormal inspiratory images. | |
| Hypersensitivity Pneumonitis (Subacute/Chronic) | Immune-mediated small airway inflammation with peribronchiolar fibrosis. | Mosaic attenuation with air trapping; three-density pattern. | |
| Cystic Fibrosis / Bronchiectasis | Chronic mucus plugging and airway destruction causing regional overinflation. | Localized hyperlucency and bronchial wall thickening; air trapping on expiratory CT. | |
| Destructive (Parenchymal) | Centrilobular Emphysema | Destruction of respiratory bronchioles, usually upper lobe–predominant in smokers. | Areas of low attenuation without visible walls; decreased vascularity. |
| Panlobular (Panacinar) Emphysema | Uniform alveolar destruction (e.g., α₁-antitrypsin deficiency). | Diffuse low attenuation, especially lower lobes; loss of vascular markings. | |
| Paraseptal Emphysema | Subpleural destruction adjacent to interlobular septa; often coexists with other forms. | Subpleural lucent spaces; may form bullae. | |
| Mechanical / Obstructive (Large Airway) | Foreign Body Aspiration | Obstruction of segmental or lobar bronchus causing distal air trapping. | Air trapping distal to obstruction; hyperinflation on expiration or decubitus view. |
| Endobronchial Tumor / Carcinoid / Obstructing Lesion | Mechanical obstruction with a “ball-valve” effect. | Unilateral or lobar hyperlucency; air trapping distal to lesion. | |
| Mucus Plugging (Asthma, CF, ABPA) | Partial airway obstruction by mucus acting as a one-way valve. | Segmental air trapping with collapse or atelectasis elsewhere. | |
| Vascular Mimics | Chronic Pulmonary Embolism | Regional hypoperfusion mimicking air trapping (vascular cause of mosaic attenuation). | Mosaic perfusion; vessels smaller in hypoperfused regions. |
| Congenital / Structural | Swyer-James-MacLeod Syndrome | Post-infectious bronchiolitis leading to unilateral hyperlucent lung. | Unilateral small, hyperlucent lung with air trapping on expiration. |
| Congenital Lobar Emphysema | Overdistension of a lobe due to bronchial cartilage deficiency or ball-valve obstruction. | Overinflated lobe with compression of adjacent lung tissue. | |
| Bronchial Atresia | Focal airway interruption with mucus impaction and distal air trapping. | Mucus-filled bronchocoele with surrounding hyperlucent area. | |
| Functional / Post-Surgical | Post-Lung Transplant (Chronic Rejection / Bronchiolitis Obliterans Syndrome) | Immune-mediated small airway obstruction leading to air trapping and graft dysfunction. | Patchy mosaic attenuation and air trapping on expiratory CT. |
| Post-Infectious Bronchiolitis (e.g., Adenovirus) | Scarring of small airways following severe infection. | Focal or diffuse air trapping, often with volume loss. |
Summary
-
Air trapping = retained gas during exhalation due to small airway or parenchymal disease.
-
Emphysema is a destructive cause of air trapping (due to loss of elastic recoil).
-
Other causes are obstructive (narrowed bronchioles) or mechanical (ball-valve lesions).
-
Expiratory CT is the gold standard for demonstrating air trapping.
Would you like me to create a visual table layout for TCV VG Med (Page 2 – Findings) with columns for Category | Mechanism | Radiologic Pattern | Example Case (image placeholder) so it fits your educational format?