Which is the superior imaging study to exclude pulmonary embolism (PE) in pregnant women: CT pulmonary angiography or lung scintigraphy ventilation/perfusion (V/Q) scans? A systematic review published July 18 in the Annals of Emergency Medicine put both exams through their paces.
Pregnant women have five times the risk of venous pulmonary embolism compared with women the same age who aren't pregnant, and if it's left untreated, mortality rates in these women can be as high as 9%, according to co-authors Dr. Latha Ganti and Dr. David Lebowitz from the University of Central Florida. However, treating PE with heparin can create additional risks if a PE diagnosis is not confirmed.
Ganti and Lebowitz noted that while CT pulmonary angiography has been considered the standard for PE diagnosis for years, lung scintigraphy has recently found favor due to concerns about radiation exposure from CT. Therefore, they decided to perform a meta-analysis of both modalities and their effectiveness in excluding a diagnosis of PE.
They searched Medline and Embase, settling on 11 research studies that included a total of 695 CT pulmonary angiography exams and 665 lung scintigraphy studies. Lung scintigraphy was performed using a variety of techniques, such as V/Q scanning, perfusion-only scanning, and V/Q SPECT. The study population had a PE prevalence of 3.3%.
How did the modalities stack up? Both were comparable for most diagnostic metrics, the authors found. While CT pulmonary angiography lagged in the initial sensitivity analysis, its numbers improved to 100% after the authors performed a data adjustment in which inconclusive test results followed by treatment were assumed to be positive.
| Imaging modalities for diagnosing PE in pregnant women | ||
| CT pulmonary angiography | Lung scintigraphy | |
| Median sensitivity | 83% | 100% |
| Median adjusted sensitivity | 100% | 100% |
| Median negative predictive value | 100% | 100% |
| Median frequency of inconclusive results | 5.9% | 4.0% |
Ganti and Lebowitz noted that their review did not address the issue of radiation dose. They pointed out that the two exams have different mechanisms of radiation exposure, with fetal dose increasing with gestational age with CT pulmonary angiography and decreasing with gestational age for lung scintigraphy.
Both modalities deliver less than the 0.05 Gy considered to be the threshold for fetal harm by the U.S. Centers for Disease Control and Prevention. Overall, CT results in 3.4 to 6.0 times lower radiation exposure for the embryo and fetus, and in the first two trimesters, CT has 50% to 97% of the radiation dose of lung scintigraphy, they wrote.
Both CT pulmonary angiography and lung scintigraphy can be useful in evaluating suspected PE in pregnant women, they concluded. CT is more readily available and can be interpreted faster and with better interobserver agreement, while lung scintigraphy could be a good choice in cases of a normal x-ray as it limits radiation dose to the mother.
CT gets the nod if a chest x-ray is grossly abnormal, thanks to its ability to contribute to an alternative diagnosis.
