Accurate diagnosis of pulmonary embolism is important in reducing the morbidity and mortality of this disease. Diagnosis is difficult because the symptoms of pulmonary embolism are vague and nonspecific. In addition, the current “gold standard” for diagnosing pulmonary embolism is pulmonary angiography, an invasive test with a significant incidence of complications that limit its usefulness. The ventilation-perfusion radio-nuclide lung scan has been used as a noninvasive study for pulmonary embolism. The development of helical computed tomographic (CT) angiography provides another option in the evaluation of patients with suspected pulmonary embolism. Blachere and colleagues compared helical CT angiography and ventilation-perfusion radionuclide lung scanning as initial tests in the diagnosis of acute pulmonary embolism.

During an 18-month period, 216 consecutive patients suspected of having acute pulmonary embolism were evaluated by helical CT angiography, ventilation-perfusion radio-nuclide lung scan and Doppler sonography of the lower extremities. In addition, clinical information was obtained, including the clinicians' degree of suspicion of pulmonary embolism. Patients with concordance of results from ventilation-perfusion radionuclide lung scan, helical CT angiography and physician's suspicion underwent pulmonary angiography. Patients who did not have pulmonary embolism on the initial evaluation were followed for at least three months to determine if there was any recurrent thromboembolic event.

Pulmonary embolism was diagnosed in 37.9 percent (68 patients) of the patients evaluated. There was a statistically significant improvement in diagnosing pulmonary embolism with the use of helical CT angiography compared with ventilation-perfusion radionuclide lung scan. Helical CT angiography was more sensitive and specific than the ventilation-perfusion radionuclide lung scan (94.1 versus 80.8 percent and 93.6 versus 73.8 percent, respectively). Helical CT angiography also had higher positive and negative predictive values and a higher degree of interobserver agreement than ventilation-perfusion scan.

The authors conclude that helical CT angiography could replace ventilation-perfusion radionuclide lung scanning as the initial test in patients suspected of having pulmonary embolism. Helical CT angiography provided a more accurate diagnosis, thereby reducing the risk of undertreating or overtreating patients with pulmonary embolism.