Lung Density Measurements in Spontaneous Pneumothorax Demonstrate Airtrapping

Purpose: Idiopathic spontaneous pneumothorax (SP) is the result of leakage of air from the lung parenchyma through a ruptured visceral pleura into the pleural cavity. This rupture is thought to be caused by an increased pressure difference between parenchymal airspace and pleural cavity. We hypothesize that rather peripheral airway inflammation leads to obstruction with check valve phenomena and by that to airtrapping in the lung parenchyma, which precedes spontaneous pneumothorax. Setting: University hospital. Materials and methods: Forty-one matched healthy volunteers (21 smokers and 20 nonsmokers), and 41 patients with SP (21 patients with and 20 patients without bullae) underwent spirometrically controlled high-resolution CT density measurements with automatic contour tracing at 10% and at 90% of vital capacity. Results: Patients with SP showed lower mean lung density (MLD) values and higher percentages of Hounsfield units (HU) below 900 HU (pixel index [PI]) compared to the healthy volunteers on expiratory scans. This enhanced airtrapping phenomenon is seen in both the SP lung (MLD, p 002; PI, p 0.01) and the contralateral lung (MLD, p 0.009; PI, p 0.05) compared to the control subjects. The difference with control subjects is independent of smoking behavior and bullae. Conclusions: Peripheral airway obstruction with airtrapping was found, and it is supposed to play an important role in the pathogenesis of spontaneous pneumothorax. (CHEST 2004; 125:2083–2090)