Giant Bulla Vs. Pneumothorax

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.

Facts: Bulla, Giant Bulla

• 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

Distinguish Giant Bulla from Pneumothorax

• 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)

Lesson: Don't be shy to ask for a CT scan in this scenario. It is better to "do right" than "be right". The treatment is very different, and remember that the two diagnoses can coexist.

Reference:

Waseem M, Jones J, Brutus S, et al. Giant bulla mimicking pneumothorax. J Emerg Med 2005;29:155-158.