RSNA: VQ scans can be first-line defense in excluding PE during pregnancy

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Ventilation perfusion (VQ) scanning provides good diagnostic value in excluding pulmonary embolism (PE) during pregnancy, and may be utilized as a first line investigation for the condition, according to a study presented at the Radiological Society of North America (RSNA) annual conference in Chicago earlier this month.

Study presenter Silvia Tomas Hernandez, MBBS, from Glasgow Royal Infirmary in Glasgow, U.K., explained that PE is the most common preventable cause of maternal death in the U.K. and in all developed countries. “Pulmonary embolism is a diagnostic challenge, especially in late pregnancy,” she said.

The study sought to determine the value of VQ imaging as a preliminary method of diagnosis, as uncertainties exist as to what may be the best imaging modality in diagnosing PE during pregnancy. According to the study, PE often goes undiagnosed during pregnancy because its symptoms--including chest pain and shortness of breath, particularly during the third trimester—which mimic other conditions.

Hernandez said that when left undiagnosed, PE has a 30 percent mortality rate among expectant mothers.

The retrospective study included all patients admitted for suspected PE between January 2004 and December 2007. Of the 256 cases, 226 cases were ultimately reviewed. Within the patient population, the mean age was found to be 29 years (with a range of 15-46) and the mean duration of pregnancy was 30 weeks (with a range of 8-40). The study included a follow-up period of just under two years.

During the three-year research period, 218 VQ scans and eight CT pulmonary angiography (CTPA) scans were conducted on the 226 patients included in the study as the primary investigation for PE. Hernandez noted that the normal adult dose of ventilation was dispensed to the patients during the VQ scans.

In addition, some of the patients who received VQ scans were also given a chest x-ray, administered at the discretion of the clinician, explained Hernandez.  However, she further noted that the results of the chest x-rays did not merit the same diagnostic value as the VQ scans.

Hernandez explained that the VQ scans were diagnostic in 87 percent of the patient population (69 percent normal, 11 percent PE unlikely and 7 percent working diagnosis no PE). Thirteen percent of the patient population returned indeterminate results.

Approximately 10 percent of the 218 patients that underwent VQ scans proceeded to undergo CTPA scans. Of this patient population, the CTPA scans detected PE in one additional patient.

Moreover, the study found that no further thromboembolic event occurred at the follow up period and Hernandez noted the low rate of indeterminate test results, due to the VQ scans.

While a low prevalence of PE was noted in the population studied, Hernandez asserted that VQ scans can serve as a primary diagnostic tool for suspected PE, compared to CTPA.