The usefulness of chest radiographs obtained after a demonstrated perfusion scan defect in the diagnosis of pulmonary emboli.

The chest radiographs obtained within seven days of scintigraphic lung studies in 38 patients clinically suspected of having a pulmonary embolus were reviewed. Twenty-two of these patients also had pulmonary angiograms. Lung densities in areas of perfusion defects not present at the time of the scan studies were sought. Densities were observed in ten patients. These appeared 4 hours to five days later (mean 1.8 days). This sequence of events strongly supports the diagnosis of pulmonary embolism. Chest radiographs are recommended one day and, if normal, again three days after an abnormal perfusion lung scan, even if the pulmonary angiogram is normal. The delayed appearance of these lung densities will eliminate some non-emboli causes and thereby strengthen the diagnosis of embolism. If such densities are seen following a "normal" angiogram, it should be critically reviewed.