Chest radiograph shows a large lucent area in the right upper lobe with compression of the remaining lung parenchyma. In a patient with acute symptoms and no previous radiograph for comparison, this may raise a diagnostic dilemma whether it represents localized pneumothorax or just a giant bulla.
Coronal-reformatted CT image confirms the absence of pneumothorax in this case. Several bullae are clearly visualized.
- Air-filled space in the lung parenchyma due to destruction of alveolar tissue, distal to terminal bronchiole
- Larger than 2 cm in distended state
- Bullae + emphysema = bullous emphysema (can be congenital or complication of COPD)
- Giant bulla = bulla larger than one third of the hemithorax size and compression of adjacent lung parenchyma
- Important for treatment plan (bulla - no tube thoracostomy; pneumothorax - may need tube thoracostomy if large or symptomatic)
- Differentiation can be difficult on conventional radiography; they can coexist
- Helpful signs for pneumothorax: visible visceral pleural line
- Expiratory chest radiograph may help delineating a visceral pleural line of pneumothorax
- CT scan is the most accurate mean to differentiate the two diagnoses
- "Double wall" sign described in cases with ruptured bulla causing pneumothorax (air outlining both sides of the bulla wall parallel to the chest wall)