Chest
Volume 103, Issue 1, January 1993, Pages 26-29
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Clinical Investigations
Chest Radiograph—A Poor Method for Determining the Size of a Pneumothorax

https://doi.org/10.1378/chest.103.1.26Get rights and content

The ability of chest radiographs to determine the size of a pneumothorax was tested in 16 patients using computed tomographic (CT) scan as a reference method. To determine if CT with a slice thickness of 12 mm could be used, its accuracy was assessed in a lung model experiment. The lung model consisted of a water-filled plastic bag (lung) fitted into a plastic chamber (hemithorax), both of approximately the same size and shape as in man. Water was drawn off in incremental steps and a CT was done after each step. The area of the pneumothorax was calculated by computer and when multiplied by slice thickness and number of slices, the total volume of the pneumothorax could be compared with the extracted amount of water. A good correlation (r = 0.99), with the line of regression close to the line of identity, was found between the CT investigation and the artificial pneumothorax. In the patients, the size of the pneumothorax, judged by radiograph using two different methods of calculation, was correlated to the size obtained by CT. The correlation was poor (r = 0.71) irrespective of method of calculation. The size of the pneumothorax estimated by CT showed a good correlation (r = 0.99) to the initial aspirated air volumes in 12 of the 16 patients treated with drainage. A cautious attitude toward the use of chest radiographs for calculations of the degree of lung collapse in patients with pneumothorax is recommended.

Section snippets

Lung Model Experiment

A model of a pneumothorax was constructed using a water-filled plastic bag (lung) fitted into a plastic chamber (hemithorax) of the same size. The size and shape of the lung model were chosen to resemble the human hemithorax and lung as closely as possible (a cylinder of 2,500-ml volume, narrowing at the top). Water from the plastic bag was drawn off in incremental steps, and a CT scan was done after each step using a slice thickness of 12 mm. As water left the plastic bag, it decreased in size

RESULTS

The results from the lung model experiment are displayed in Figure 1. There is good agreement between the volume of extracted water and the volume of air measured by the CT scan (r = 0.99). In the clinical part of the study, the correlation between the decrease in lung volume measured by radiograph and the volume measured by CT scan is plotted in Figure 2. The correlation is poor regardless of which method is used for calculation of volumes (r = 0.71), although it differs significantly from

DISCUSSION

Every clinician faced with a case of pneumothorax has to make a choice of treatment strategy. This choice is based on the clinical condition, age, history of the patient and also on the therapeutic traditions of the hospital. The decision whether to use active treatment is to a large extent also influenced by the size of the pneumothorax. 1, 2, 3, 4, 5, 6

Chest radiography has been the most important investigational technique in patients with pneumothorax for almost a century. It is frequently

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Manuscript received March 19, revision accepted June 11.

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