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Diagnosing pulmonary embolism with helical computed tomography during pregnancy: what about exposure to iodinated contrast agents?

  1. Top of page
  2. Diagnosing pulmonary embolism with helical computed tomography during pregnancy: what about exposure to iodinated contrast agents?
  3. References

In their interesting letter about fetal radiation exposure during radiological procedures for the diagnosis of pulmonary embolism in pregnant women, Nijkeuter et al. [1] conclude that their calculation of the fetal radiation dose during helical computed tomography (hCT) justifies performing this objective diagnostic test as a first-line test in pregnancy. This conclusion raises two comments.

First, to date, the use of hCT as a single test for ruling out the diagnosis of pulmonary embolism has not been validated. Indeed, in series in which a lower limb venous compression ultrasound and a single-detector helical row CT were performed in suspected pulmonary embolism [2,3], the proportion of patients found to have deep venous thrombosis despite negative results on hCT was 6–8%, implying that lower limb ultrasound must be combined with hCT to definitely rule out the diagnosis of pulmonary embolism if both tests are negative. Moreover, lower limb ultrasound is a non-invasive test and is totally safe for the fetus. Even if its diagnostic performance for isolated iliac deep vein thrombosis, which is reported to be more prevalent during pregnancy, is not as good as that described at the lower limb level, this examination allows, if positive, to rule in the diagnosis of pulmonary embolism without further testing in about one of two patients with pulmonary embolism. Therefore, we believe that it should remain the first-line test in pregnant women with suspected pulmonary embolism. The advent of multi-detector hCT, allowing an improved visualization of the pulmonary arteries, raises the possibility that pulmonary embolism might be safely ruled out without performing a lower limb venous ultrasound, but this has not been confirmed yet.

Second, although the lower fetal radiation dose with hCT as compared with other diagnostic tests is appealing, another issue is the exposure of the fetus to iodinated contrast medium during hCT, which is one of the main causes of neonatal hypothyroidism. Even vaginal antiseptics and skin disinfectants containing iodine might cause neonatal hypothyroidism if applied during pregnancy and delivery [4]. Therefore, the risk of fetal hypothyroidism seems real, even for very low doses of iodine, and it seems wise to further evaluate the prevalence, risk factors (type and volume of contrast media, iodine concentration) and long-term outcome of this possible adverse effect before recommending generalized use of hCT for the diagnosis of pulmonary embolism in pregnant women.

References

  1. Top of page
  2. Diagnosing pulmonary embolism with helical computed tomography during pregnancy: what about exposure to iodinated contrast agents?
  3. References
  • 1
    Nijkeuter M, Geleijns J, De Roos A, Meinders AE, Huisman MV. Diagnosing pulmonary embolism in pregnancy: rationalizing fetal radiation exposure in radiological procedures. J Thromb Haemost 2004; 2: 18578.
  • 2
    Musset D, Parent F, Meyer G, Maitre S, Girard P, Leroyer C, Revel MP, Carette MF, Laurent M, Charbonnier B, Laurent F, Mal H, Nonent M, Lancar R, Grenier P, Simonneau G. Diagnostic strategy for patients with suspected pulmonary embolism: a prospective multicentre outcome study. Lancet 2002; 360: 191420.
  • 3
    Perrier A, Howarth N, Didier D, Loubeyre P, Unger PF, De Moerloose P, Slosman D, Junod A, Bounameaux H. Performance of helical computed tomography in unselected outpatients with suspected pulmonary embolism. Ann Intern Med 2001; 135: 8897.
  • 4
    Weber G, Vigone MC, Rapa A, Bona G, Chiumello G. Neonatal transient hypothyroidism: aetiological study. Italian Collaborative Study on Transient Hypothyroidism. Arch Dis Child Fetal Neonatal Ed 1998; 79: F702.