Diagnosing Pulmonary Embolism with Multidetector-Row CT

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Diagnosing Pulmonary Embolism with Multidetector-Row CT

Newer-generation CT scanners might allow PE to be ruled out without ultrasonography.

A limitation of first-generation helical computed tomography (CT) for the diagnosis of pulmonary embolism (PE) is its low sensitivity for imaging small peripheral arteries. In this study, French and Swiss researchers incorporated newer technology -- 4-slice multidetector-row CT -- into a diagnostic algorithm for 756 patients with suspected PE. The objective was to see whether ultrasonography of leg veins is still necessary with this protocol.

Patients with low-to-intermediate clinical probabilities of PE, according to the previously validated Geneva score (Arch Intern Med 2001; 161:92), underwent D-dimer testing; patients with normal results underwent no further evaluation. Those with abnormal D-dimer results, plus all patients with high clinical probabilities of PE, underwent both multidetector-row CT and leg ultrasonography. PE was diagnosed in 194 patients; CT alone would have established these diagnoses in 187 of the 194. Only 3 patients had positive leg ultrasonography and negative, but technically adequate, CT; the remaining 4 patients were diagnosed by further evaluation after inconclusive CT results.

Patients were followed for 3 months. According to an algorithm that included only D-dimer and CT results (but not ultrasound), the maximum 3-month incidence of PE among untreated patients in whom PE was "ruled out" would have been only 1.5%.

Comment: These findings suggest that newer-generation CT scanners -- which now are available in many centers -- can rule out PE adequately, without a need to perform leg ultrasound in patients with negative CT. However, the success of the algorithm used in this study depends upon a reliable D-dimer assay and accurate assessment of pretest clinical probability.

— Allan S. Brett, MD

Published in Journal Watch General Medicine April 29, 2005