Preliminary Diagnosis: Pulmonary Embolism (PE)

I. What imaging technique is first-line for this diagnosis?

Computed tomographic angiography (CTA) utilizing PE protocol.

II. Describe the advantages and disadvantages of this technique for diagnosing pulmonary embolism.

Advantages

  • Diagnostic for pulmonary embolisms of clinically significant size.

  • Relatively quick imaging procedures.

    Continue Reading

  • Requires minimal patient cooperation.

  • Offers excellent anatomic detail of the thorax, including lung parenchyma, airways, and chest wall.

  • Can help differentiate between chronic and acute pulmonary embolic events.

Disadvantages

  • Exposes the patient to a large amount of ionizing radiation.

  • Exposes the patient to the risk of contrast induced nephropathy.

  • Exposes the patient to the risk of contrast induced allergic reaction.

III. What are the contraindications for the first-line imaging technique?

  • Known contrast allergy.

  • Pregnancy, especially during the first two trimesters.

  • Creatinine > 1.6. Exceptions can be made on a case-by-case basis.

IV. What alternative imaging techniques are available?

  • Ventilation perfusion (V/Q) nuclear medicine scan.

  • Conventional angiography.

  • Ultrasound of the lower extremities, with and without Doppler.

V. Describe the advantages and disadvantages of the alternative techniques for diagnosing pulmonary embolism.

Ventilation perfusion (V/Q) nuclear medicine scan
Advantages

  • May be used in circumstances when intravenous iodinated contrast is contraindicated.

  • Preferred in a pregnant patient (utilizing only the perfusion portion of the exam with half the dose of Technetium 99m-MAA. The ventilation portion of the exam is omitted to reduce radiation dose to the pregnant patient).

  • Can be diagnostic for pulmonary embolus.

  • Uses a very small dose of ionizing radiation, much less than CTA.

Disadvantages

  • The exam takes about an hour to complete. The patient must be able to tolerate lying supine for the length of the exam.

  • May be more difficult to interpret and less accurate than CTA.

  • Requires the appropriate handling of radioactive nuclear tracers.

  • The hospital must be equipped with proper waste disposal for nuclear tracers.

Conventional angiography
Advantages

  • Diagnostic gold standard for pulmonary embolism.

  • Can be therapeutic if direct intraluminal thrombolysis is indicated.

  • Can determine flow dynamics and pressures within the pulmonary arteries.

Disadvantages

  • Invasive and associated with a higher morbidity than CTA or V/Q scans.

  • Does not demonstrate the anatomical detail of a CT or MRI.

  • Requires the use of iodinated contrast, which can be associated with an allergy or contrast induced nephropathy.

  • Uses a high dose of radiation.

  • Expensive.

  • Requires a fluoroscopy suite and interventional radiology.

  • Sedation is recommended.

Ultrasound of the lower extremities with and without doppler
Advantages

  • This adjunctive imaging exam can help rule in or out deep venous thrombosis as an underlying cause for pulmonary embolism.

  • Lack of ionizing radiation, particularly advantageous when imaging a pregnant patient.

  • Lack of contrast administration, particularly advantageous when imaging a patient with renal failure or creatinine > 1.6.

  • Relatively cheap and fast real time imaging evaluation.

  • Noninvasive.

  • Ultrasound of the lower extremities, with and without Doppler, is a useful imaging study in pregnant patients, patients with renal abnormality, patients in which CTA or VQ scans are relatively contraindicated, and patients with negative/equivocal imaging findings.

Disadvantages

  • The quality of the exam is operator dependent.

  • Large body habitus and/or the presence of central lines or overlying bandages secondary to trauma or recent procedure can limit visibility of the lower extremity veins and can thereby reduce the sensitivity and/or specificity of the exam.

VI. What are the contraindications for the alternative imaging techniques?

Ventilation perfusion (V/Q) nuclear medicine scan

  • Pregnancy is a contraindication for the ventilation portion of the exam.

  • While not an absolute contraindication, breastfeeding patients must be counseled not to breastfeed for approximately 24 hours.

Conventional angiography

  • Coagulopathy, i.e., bleeding diathysis.

  • Pregnancy.

  • Creatinine > 1.6.

  • Allergy.

References

Bettmann, MA. “ACR Appropriateness Criteria® acute chest pain–suspected pulmonary embolism.”. J Thorac Imaging. vol. 27. 2012. pp. W28-31. http://www.acr.org/~/media/186992e39e754270bb3abbf44a5a5801.pdf

Copyright © 2017, 2013 Decision Support in Medicine, LLC. All rights reserved.

No sponsor or advertiser has participated in, approved or paid for the content provided by Decision Support in Medicine LLC. The Licensed Content is the property of and copyrighted by DSM.

Jump to Section