Expiratory chest radiographs do not improve visibility of small apical pneumothoraces by enhanced contrast

Demonstration of small apical pneumothoraces is supposed to be facilitated by expiratory chest radiographs. This study aimed to analyse the assumed enhancement of visual contrast on expiratory chest radiographs in patients with small apical pneumothoraces. Optical densities (OD) were obtained with a densitometer (X-rite 3001) on 54 paired inspiratory and expiratory chest radiographs of 22 consecutive patients with small apical pneumothoraces. The ODs were measured: at the intervertebral space between the first and second thoracic vertebrae (Area 1); at the peripheral part of the affected lung parenchyma (Area 2); and at the adjacent intrapleural space (Area 3). Excellent correlations of OD of each area were obtained between paired inspiratory and expiratory chest radiographs. The ODs of all areas on expiratory chest radiographs were significantly higher than on inspiratory chest radiographs. Contrast between pulmonary parenchyma and intrapleural air in inspiratory and expiratory films did not differ significantly. Expiratory chest radiographs do not improve visibility of small apical pneumothoraces by enhanced contrast between pulmonary parenchyma and intrapleural air. Expiratory chest radiographs show equally increased OD in the area of lung tissue and intrapleural air, caused by increased extrapulmonary tissue density during expiration, resulting in increased radiation exposure monitored by the ionization chambers of standard radiological equipment. If expiratory chest radiographs are really improving the visibility of apical pneumothoraces, there must be other reasons than contrast enhancement to explain this.