CT diagnosis of pulmonary embolism: Ready for prime time?

The currently accepted diagnostic tests for the detection of acute pulmonary embolism (PE) are the ventilation/perfusion (V/Q) scan and pulmonary angiography. The major studies assessing the utility of the V/Q scan are reviewed. In a majority of cases, the V/Q scan is nondiagnostic, necessitating further testing, that is, pulmonary angiography. This is a procedure that is expensive, underused, and not universally available. Although the diagnostic gold standard, it too has limitations, especially in the setting of small, subsegmental clots. With the recognition that deep vein thrombosis and PE are manifestations of the same disease process, diagnostic algorithms were developed that included noninvasive imaging of the lower extremities to document the presence or absence of proximal vein thrombosis. This limits the need for pulmonary angiography and is believed to be cost- effective; however, despite multiple studies and publications, these algorithms are underused. Helical CT technology is a minimally invasive procedure that provides excellent visualization of the pulmonary vasculature in a short time, with a small amount of intravenous contrast. This not only provides the clinician with a direct view of pulmonary emboli but often reveals an alternative diagnosis if PE is absent. The literature assessing the diagnostic yield of helical CT is reviewed, and the potential role of helical CT in the diagnosis of acute PE is discussed. Lastly, a new diagnostic algorithm using helical CT is proposed.