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Pulmonary Embolism Diagnosis with Multidetector CT

Does CT venography add advantages to CT angiography alone in the context of concordant clinical assessment?

We don’t yet know the best approach to diagnosing pulmonary embolism (PE). To assess the accuracy of contrast-enhanced multidetector computed tomographic angiography (CTA), researchers conducted a publicly funded study comparing CTA alone with CTA plus venous-phase multidetector CT venography (CTV). Of 1090 adults with suspected PE (mean age, 52; 62% women) enrolled at eight centers, 824 were assessed according to a diagnostic reference standard involving clinical evaluation; CTA-CTV; ventilation-perfusion scanning; venous compression ultrasonography of the lower extremities; and, if the noninvasive tests could not diagnose or rule out PE, pulmonary digital-subtraction angiography.

Of the 824 fully evaluated patients, 192 (23%) received diagnoses of PE with the composite reference standard. Measured against that standard, CTA results (interpretable in 773 patients) had 83% sensitivity, 96% specificity, a positive predictive value (PPV) of 86%, and a negative predictive value (NPV) of 95%. Combination CTA-CTV results (interpretable in 737 patients) had 90% sensitivity, 95% specificity, a PPV of 85%, and an NPV of 97%.

When clinical assessment of the probability of PE was considered, CTA and CTA-CTV each had a PPV of 96% in patients with high clinical probability of PE; PPVs were 92% and 90%, respectively, in patients with intermediate clinical probability. In patients with low clinical probability of PE, false-positive rates for CTA and CTA-CTV, respectively, were 42% and 43%, and NPVs were 96% and 97%.

Comment: For PE diagnosis, CTA-CTV has a higher sensitivity and a similar specificity compared with CTA alone. False positives were common with both methods when the clinically determined probability of PE was low. Taking note of recent findings of favorable prognoses in patients with normal CTA results (e.g., Journal Watch Cardiology Feb 9 2006), the editorialist states that the improved sensitivity with CTV does not justify the additional radiation exposure. Also, we must remember that a patient’s clinical characteristics are always important to consider, for even a good test produces many false positives in low-risk patients.

— Harlan M. Krumholz, MD, SM

Published in Journal Watch Cardiology June 28, 2006

Citation(s):

Stein PD et al. for the PIOPED II Investigators. Multidetector computed tomography for acute pulmonary embolism. N Engl J Med 2006 Jun 1; 354:2317-27.

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Perrier A and Bounameaux H. Accuracy of outcomes in suspected pulmonary embolism. N Engl J Med 2006 Jun 1; 354:2383-5.

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• Medline abstract (Free)