CT pulmonary angiography (CTPA) does not appear to miss pulmonary emboli detected with ventilation-perfusion (V/Q) scanning, new research suggests.

by Anthony J. Brown, MD

CT pulmonary angiography (CTPA) does not appear to miss pulmonary emboli detected with ventilation-perfusion (V/Q) scanning, new research suggests.

In fact, more pulmonary emboli were detected with CTPA than with V/Q scanning, although the clinical relevance of the emboli seen only with the former remains to be determined, according to the report in the Journal of the American Medical Association for December 19.

V/Q scanning has been used to evaluate suspected pulmonary embolism for 30 years, the authors note. With this modality, the results are reported as being low, intermediate, or high probability for a pulmonary embolism. While a high probability result strongly suggests pulmonary embolism, the meaning of a low or intermediate result is much less clear.

CTPA results, by contrast, are clearer, being either positive or negative for pulmonary embolism. In addition, CTPA offers the advantage of detecting non-thrombotic causes of the patient's symptoms.

At many centers, CTPA has replaced V/Q scanning in evaluating suspected pulmonary embolism, yet formal comparisons between the two have been limited. Moreover, concerns have been raised that CTPA is not as sensitive as V/Q scanning.

"Ours was the first randomized study to directly compare the utility of two radiology tests (V/Q scanning and CTPA) for excluding the diagnosis of pulmonary embolism," lead author Dr. David R. Anderson, from Queen Elizabeth II Health Sciences Center in Halifax, Nova Scotia, told Reuters Health.

In the study, Dr. Anderson and colleagues assessed the outcomes of 1417 patients with suspected pulmonary embolism who were randomized to undergo CTPA or V/Q scanning. Overall, 19.2 per cent of CTPA patients and 14.2 per cent of V/Q scanned patients were diagnosed with pulmonary embolism and treated with anticoagulant therapy.

"Further research is necessary to understand the clinical significance of pulmonary embolism detected by CTPA," Dr. Anderson said. "Is there a subset of patients with relatively limited pulmonary embolism detected by CTPA who do not require anticoagulation treatment?"

Patients thought not to have pulmonary embolism did not receive anticoagulant therapy and were followed for three months. The main outcome measure was the occurrence of symptomatic pulmonary embolism or proximal deep vein thrombosis in these patients.

Subsequent venous thromboembolism developed in 0.4 per cent of those in the CTPA group and one per cent of those in the V/Q scan group during follow-up. One fatal case of pulmonary embolism occurred in the V/Q scanning group.

In a related editorial, Dr. Jeffrey Glassroth, from Northwestern University in Chicago, comments that "at the current state-of-the-art, CTPA, using multidetector scanners, appears to be an excellent imaging choice unless there is a contraindication to dye administration, or perhaps in pregnancy because of the higher dose of radiation with CTPA."


Source: Reuters