Multislice CT Scans Effective in Detection of Pulmonary Embolisms without Ultrasonography

In detecting pulmonary embolisms (PE), it is just as effective to use D-dimer measurement in combination with a multislice computed tomography scan (MSCT) as opposed to D-dimer venous ultrasonography of the leg and MSCT. This means that venous ultrasonography may no longer be needed to diagnose PE when MSCT is used, according to a recent report.

Pulmonary embolisms are blood clot blockages of the pulmonary artery. To from this, a venous clot may form and detach from its point of attachment, flowing into the arterial system. Detection of PE currently includes clinical probability assessment (CPA) with subsequent sequential diagnostic tests, such as the D-dimer, ultrasonography, and CT scans.

A CT chest scan uses composite X-rays to form a three-dimensional image. Chest CT scans are considered a promising new method to visualize pulmonary clots, but the single slice CT has a low sensitivity for detecting PE (approximately 70%,) which limits its possibilities as an independent test. In contrast, an MSCT is able to make several images in a similar way, simultaneously. MSCT has provided new potential to replace pulmonary angiography because it allows a more effective visualization of the segmental and subsegmental vessels. D-dimer ultrasonography involves detection of a protein present in the blood after a blood clot forms.

To investigate the relative accuracy of these diagnostic techniques, Dr. Marc Righini, from the Geneva University Hospital and Faculty of Medicine (Switzerland), and colleagues, performed a randomized controlled trial of 1819 outpatients who were clinically suspected of having PE. They compared two strategies for diagnosis: the first (DD-CT), with 903 patients, evaluated CPA combined with D-Dimer measurement and MSCT; the second (DD-CT-US), with 916 patients, was the same but included venous ultrasonography of the leg. The effectiveness was quantified by calculating the three-month risk of recurrent deep vein thrombosis or PE in patients who were left untreated because they had been excluded by either strategy. The investigators published their findings in the April 18, 2008, issue of the journal The Lancet.

The prevalence of PE was 20.6% in both groups. There were 186 in the DD-CT group and 189 in the DD-CT-US group. After these patients were removed from the population, 838 remained DD-CT and 855 DD-US-CT. Later examination showed that the three-month risk of PE was 0.3% in both groups--meaning that both strategies were equally effective. Compared to the old method, which requires lung scans with nuclear medicine techniques, MSCT would be easier and more widely available to doctors.

The investigators ultimately reported that ultrasound is not completely necessary in the diagnosis of PE. "We conclude that ultrasound is not needed to rule out pulmonary embolism when MSCT is used. An ultrasound could be of use in patients with a contraindication to CT.”

Prof. Paul Kyrle and Prof. Sabine Eichinger, from the Medical University of Vienna (Austria) contributed a comment in which they said, "This approach will facilitate the diagnostic work-up of patients with suspected pulmonary embolism and seems to be cost-effective.” They additionally discussed new treatments for PE, including phase III clinical trials.


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