Objective: The aim of this study was to define the relationship between interpleural distance measurements on an erect posteroanterior chest radiograph and pneumothorax size as measured by helical CT in a series of patients.
Subjects and methods: Twenty pneumothoraces from 19 patients (10 males, nine females) were analyzed. Most pneumothoraces were on the right side (n = 16). The etiology was spontaneous in seven patients and iatrogenic in thirteen. All patients underwent an erect inspiratory posteroanterior radiograph and a helical CT scan of the thorax on the same visit to the radiology department. The interpleural distance was measured at three locations and the figures added together. Following helical CT of the thorax, the percentage pneumothorax size was calculated by drawing regions of interest around the relevant hemithorax and lung on 10-mm reconstructed slices. A scattergram of the sum of interpleural distances in centimeters versus percentage pneumothorax size was plotted.
Results: Analysis of results showed that percentage pneumothorax size could be calculated by the formula Y = 4.2 + [4.7 x (A + B + C)], r = .98, p < .0001.
Conclusion: This study identified a formula for accurately calculating percentage pneumothorax size as determined by helical CT from an erect posteroanterior radiograph. Using this formula with the clinical status of the patient should more easily identify patients requiring active intervention.