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.


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

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