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Imaging for the Diagnosis of Pulmonary Embolism in Pregnant Women

Three Part Question

In [Pregnancy with pulmonary embolism], is [Computed-Tomographic pulmonary angiography better than Ventilation (V) –Perfusion (Q) scintigraphy] for [detection of pulmonary embolism]?

Clinical Scenario

A 27-year-old female presents to the emergency department with shortness of breath. She is 26 weeks pregnant. The lower limbs Doppler ultrasound is negative. You must perform another diagnostic test to eliminate a pulmonary embolism. You wonder which test is the most appropriate for this patient: a Computed-Tomographic pulmonary angiography or a ventilation-perfusion scintigraphy.

Search Strategy

A. No BestBETs or critical appraisal was found on this topic specifically.
B. There was no Cochrane review found on the subject
C. Embase search
D. Pubmed search
C. Embase search result date of search 09/01/2013 :
#1 pregnancy’/exp OR pregnancy 881,040
#2 pulmonary AND (\\\\\\\\\\\\\\\'embolism\\\\\\\\\\\\\\\'/exp OR embolism) 45,655
#3 (#1 AND #2) 2,308
#4 computed tomographic angiography\\\\\\\\\\\\\\\'/exp OR \\\\\\\\\\\\\\\'computed tomographic angiography\\\\\\\\\\\\\\\' 13,588
#5 (#3 AND #4) 79
#6 \\\\\\\\\\\\\\\'ventilation\\\\\\\\\\\\\\\'/exp OR ventilation AND (\\\\\\\\\\\\\\\'perfusion\\\\\\\\\\\\\\\'/exp OR perfusion) 16,749
#7 (#5 AND #6) 29

From this review, 2 were relevant

D. Medline via the Pubmed interface search date 09/01/2013
#1 Pregnancy: 714830
#2 Pulmonary embolisms: 37576
#3 Computed-tomographic angiography: 3494
#4 Ventilation perfusion: 12219
#1 and #2: 1922
#1 and #2 and #3: 11
#1 and #2 and #3 and #4: 4

From this review, 3 were relevant

The Cochrane Library issue 12 of 12 2012

MeSH descriptor: (Pulmonary Embolism) explode all trees AND MeSH descriptor: (Pregnancy) explode all trees 1 article 0 relevant

Search Outcome

A total of 4 unique resources were found relevant

Relevant Paper(s)

Author, date and country Patient group Study type (level of evidence) Outcomes Key results Study Weaknesses
Ridge et al,
Pregnant women. Q scan :25 CT pulm Angio :25 P≥0.05 for age/trimester. Retrospective analysisAdequacy of diagnosisRate of inadequate diagnosis lower with Q Scan (4% vs 35.7%) P≤0.0058Retrospective. Few patients (50). All patients had normal Chest X-Rays in the Q scan group.
Cause of non-diagnosisCT Angio technique is not totally adapted to the hemodynamic changes associated with pregnancy
Cahill et al,
Pregnant women or up to 6 weeks post-partum. V/Q Scan : 196 CT pulm Angio : 108 P≥0.05 for age/trimester. Retrospective cohort Adequacy of diagnosisRate of inadequate diagnosis is slightly higher in CT angiography P= 0.38 Retrospective. 4 to 16-multidetector row CT scan. CT angio : 62% post partum.
Diagnostic or non-diagnosticAll non-diagnostic exam : CT angio 17%, V/Q scan 3.2%
Chest X-ray abnormal Non-diagnostic exam : Ct angio 16.4%, V/Q scan 40%
Shahir et al,
Pregnant women CT pulm Angio : 106 Q scan : 99 Retrospective cohortAdequacy of diagnosis with follow up at 3 months (Clinical, CT angio or perfusion scan and initiation of anticoagulation if needed) CT angio: PE 5/106 (4 diagnosed, 1 missed), Perfusion scan: PE 0/99 (None missed) Retrospective. 8 to 64-multidetector row CT scan. Initial reading by locals with variable experience and expertise. Subsequent double reading by the study radiologists. Low percentage of PE.
Quality of imagingCT angio: Good 76.4%, Acceptable 17.9%, Poor 5.6%. Perfusion scan: Normal 63, very low probability 14, Low probability 19, Incomplete 3
Clinical negative predictive value (NPV) CT angio: NPV: 99%, Perfusion scan: NPV 100%
Tests are equivalent
Revel et al,
Pregnant women. V/Q scan : 91 CT pulm Angio : 43 P≥0.05 for age/trimester. Retrospective analysis. Expert reviewer.Adequacy of diagnosis: Negative (N), Indeterminate (I), Positive (P) V/Q scan : 70% N, 19% I, 11% P. CT Angio : 75% N, 19% I, 16% P. Rate of inadequate diagnosis is the same Retrospective. 13 of the 91 V/Q scans were from after 2006. The majority of CT Angio were from after 2006. Outcome not available in 11 patients.
Interobserver agreement V/Q scan : Kappa = 0.75, CT Angio : Kappa = 0.84
CT Angio better for alternate diagnosis


These four retrospective studies looked at the diagnostic performance of CTPA and lung scintigraphy. The CT scanners were 64-multidetector row (Ridge, Revel), four to 16-multidetector row (Cahill) or eight to 64-multidetector rows (Shahir). The lung scintigraphy protocol used in Ridge and Shahir was perfusion only and a perfusion/ventilation protocol was used in Revel and Cahill. The irradiation on breast tissue is higher with CT than scintigraphy (8×). The fetal irradiation is minimal with both tests. Even if CT is better than lung scintigraphy in normal patients, the haemodynamic changes in pregnant women make CT angiography less optimal for PE detection, even with state-of-the-art CT technology. Timing with perfusion protocol can be hard to synchronise. Only one study (Ridge) found a statistical difference in favour of lung scintigraphy compared to CT angiography in pregnant woman with suspected PE. These two tests yield approximately the same diagnostic percentage in the three other studies. We should give priority to the test that causes less harm to the patient. The choice of test may also depend on the possibility of an alternative diagnosis for shortness of breath (if abnormal chest x-ray), in which CT angiography is better but with a higher breast cell irradiation. The American Thoracic Society also leans towards this avenue in their 2011 expert recommendations.

Editor Comment

CTPA, CT pulmonary angiography; NPV, negative predictive value; PE, pulmonary embolism; VQ, ventilation–perfusion.

Clinical Bottom Line

For the diagnosis of PE in pregnancy, if imaging is needed, a VQ (or perfusion) scan should be prioritised if the chest x-ray is normal. In the case of an abnormal chest x-ray, a CTPA scan will be better in finding an alternative diagnosis.


  1. Ridge CA, McDermott S, Freyne BJ, et al. Pulmonary Embolism in Pregnancy: Comparison of Pulmonary CT Angiography and Lung Scintigraphy. Am J Roentgenol 2009;193:1223–7.
  2. Cahill AG, Stout M, Macones GA, et al. Diagnosing Pulmonary Embolism in Pregnancy Using computed-Tomographic angiography or Ventilation-Perfusion. Obstet Gynecol 2009;114:124–129.
  3. Shahir K, Goodman LR, Tali A, et al. Pulmonary Embolism in Pregnancy: CT Pulmonary Angiography Versus Perfusion Scanning. Am J Roentgenol 2010;195:W214–20.
  4. Revel MP, Cohen S, Sanchez O, et al. Pulmonary Embolism during Pregnancy: Diagnosis with Lung Scintigraphy or CT Angiography? Radiology 2011;258:590–8.