Right mainstem bronchus is more commonly affected than left — it is more vertical, larger in caliber, and more directly aligned with the trachea. Adults with decreased consciousness or dental procedures: lower lobe predilection. Children: right > left. Organic/vegetable material (peanuts, nuts) is radiolucent on XR — CT required.
CT Findings
| Finding | Mechanism | Notes |
|---|---|---|
| Obstructive emphysema (air trapping) | Ball-valve effect: air enters on inspiration, cannot exit on expiration; hyperlucent lobe/lung | Most common early finding; best seen on expiratory CXR or expiratory CT; contralateral mediastinal shift on expiration (Holzknecht sign); mosaic attenuation on CT |
| Atelectasis | Complete obstruction with absorption of distal air; lobar or segmental collapse; absent distal air bronchograms | More common with complete occlusion; right lower lobe most common in adults; may develop over hours to days |
| Post-obstructive pneumonia | Retained secretions distal to obstruction lead to bacterial overgrowth; consolidation in obstructed lobe/segment | Recurrent consolidation in identical location = foreign body or endobronchial lesion until proven otherwise |
| Direct visualization | Radio-opaque objects (metal, bone, teeth) visible directly; radiolucent objects: bronchial wall thickening, surrounding air trapping, soft-tissue density within airway lumen | Thin-slice CT with multiplanar reformats; virtual bronchoscopy aids localization; bronchoscopy is both diagnostic and therapeutic |
Recurrent consolidation in the same anatomic location = foreign body or endobronchial lesion until proven otherwise. CT with thin slices and multiplanar reformats is essential. Bronchoscopy is both diagnostic and therapeutic.
Expiratory CT Technique
Expiratory CT (or lateral decubitus XR) reveals air trapping that may be subtle or invisible on inspiratory imaging:
- The obstructed lung remains hyperlucent on expiration (fails to increase in density)
- Contralateral normal lung increases in density normally
- Mediastinal shift toward the normal lung on expiration (Holzknecht sign on fluoroscopy/CXR)