Comparison of lung scintigraphy and CT angiography in the diagnosis of pulmonary embolism

In our institution, as in others, pulmonary angiography is not used in the diagnosis of pulmonary embolism because of its perceived risks. We compared the results on lung scintigraphy and computed tomography angiography (CTA) in 116 consecutive patients with suspected pulmonary embolism. In 14 patients with normal lung scans 13 (93%) were also normal with CTA. In the 73 patients with low probability lung scans only five (7%) demonstrated pulmonary embolism with CTA. In 12 patients with high probability lung scans 11 (92%) demonstrated pulmonary embolism on CTA. However, in the 17 patients with intermediate probability lung scans, 10 (58.8%) showed embolism with CTA. We conclude that wherever practicable lung scans should be performed in all patients due to its relatively low radiation burden and that CTA be performed in patients with intermediate probability scans due to the high incidence of pulmonary embolism. Patients with either a normal scan or high probability scan should be treated appropriately. In patients with low probability scans CTA should be performed in those with a high clinical suspicion of thromboembolism.