August 12, 2010

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.

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

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