Imaging

Pulmonary Hypertension

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Preliminary Diagnosis: Pulmonary Hypertension

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

Chest X-ray, PA, and lateral.

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

Advantages

  • Cost-effective and quick.

  • Can show the diameter of the right interlobar pulmonary artery, which is considered abnormal if it measures > 16 mm in males and > 14 mm in females.

  • Can reveal underlying causes of pulmonary hypertension, such as diffuse lung disease, including emphysema and interstitial lung disease.

Disadvantages

  • Not very sensitive. Chest radiography has a sensitivity of 50% for mild hypertension and 75% for severe hypertension

  • Not as sensitive or specific as Computed Tomography/Computed Tomography Angiography (CT/CTA)

  • Cannot determine if pulmonary thromboembolic disease is an contributing factor to pulmonary hypertension

  • Involves a minimal amount of ionizing radiation.

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

None. Some institutions may require consent for pregnant patients.

IV. What alternative imaging techniques are available for this diagnosis?

Computed Tomography Angiography (CTA) of the chest, which requires IV contrast.

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

Advantages

  • Highly specific and sensitive for pulmonary hypertension. Up to 100% specificity when the transverse diameter of the main pulmonary artery is ≥ 29 mm. Up to 89% sensitivity in patients with advanced lung disease.

  • Relatively quick procedure that requires minimal patient cooperation and is less susceptible to motion artifact.

  • Provides excellent anatomic detail of pulmonary vessels. It allows accurate visualization of vessel diameter, arterial calcifications, collateral circulation, intraluminal clots and signs of chronic thromboembolism.

  • A major advantage is the ability to assess for underlying causes of pulmonary hypertension, including chronic obstructive pulmonary disease and pulmonary thromboembolic disease. While underlying pulmonary thromboembolic disease is not the most common cause of pulmonary hypertension, it is very important to rule out.

  • Useful modality to screen for arterial disease. It is safer, less invasive, more cost-effective and less time-consuming than angiography.

Disadvantages

  • Exposes the patient to a significant dose of ionizing radiation.

  • There is a risk of allergic reaction to contrast material.

  • Should be avoided in patients with kidney disease, as contrast material can further harm kidney function.

  • Cannot give an estimate or direct measurement of the pulmonary artery pressure like echocardiography or right heart catheterization, respectively.

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

  • May be contraindicated in pregnancy.

  • Relative contraindication in patients with renal failure.

  • Relative contraindication in patients with contrast allergy.

Which two complementary imaging examinations are considered most appropriate in the evaluation for pulmonary hypertension, when ordered together?

Transthoracic Doppler Ultrasound Echocardiography and Right Heart Catheterization. These two studies are complementary, although echocardiography is typically performed prior to catheterization.

The American College of Radiology appropriateness criteria designates the combination of these two exams as the most appropriate utilization of exams in the work up of pulmonary hypertension of unknown cause, likely because the combination of the exams acquires functional and anatomical information of the heart as well as the pulmonary artery pressure, which can be used to diagnose pulmonary hypertension unequivocally.

Describe the advantages and disadvantages of the two complementary imaging examinations for diagnosing pulmonary hypertension.

Transthoracic Doppler Ultrasound Echocardiography[

Advantages

  • Noninvasive

  • Widely available

  • Reproducible

  • Relatively cheap

  • No radiation dose to the patient or examiner

  • Great exam for screening and serial follow up

  • Can estimate right ventricular systolic pressure, pulmonary diastolic pressure, and pulmonary arterial pressure

  • Can evaluate cardiac anatomy for ventricular enlargement and function, valvular function and morphology, pericardial effusion, and presence of a shunt

Disadvantages

  • Operator dependence, accoustic window restrictions, and reduced sonographic penetration secondary to large patient body habitus can contribute to suboptimal exam.

Right Heart Catheterization

Advantages

  • Considered the "gold standard" for the diagnosis of pulmonary arterial hypertension.

  • Directly measures pulmonary arterial pressure and cardiac function.

  • Can measure vasoreactivity of pulmonary circulation which can identify patients more likely to benefit from long-term calcium channel blocker therapy.

Disadvantages

  • Invasive, with morbidity rate of 1.1% and morality rate of 0.055%.

  • Ionizing radiation exposure.

  • Use of iodinated contrast.

  • Expensive and requires use of a cath lab suite and ancillary team.

  • Sedation.

  • Repeat catheterization is required for follow up to assess response to therapy.

What are the contraindications for the two complementary imaging examinations?

Transthoracic Doppler Ultrasound Echocardiography

  • None.

Right Heart Catheterization

  • Coagulopathy, i.e., bleeding diathesis.

  • Pregnancy.

  • Creatinine > 1.6.

  • Allergy.

What is another alternative imaging technique particularly useful for excluding chronic thromboembolic pulmonary hypertension, although it is considered less appropriate than CTA by the American College of Radiology?

Ventilation-Perfusion (V/Q) Nuclear Medicine Scan

What are the advantages, disadvantages, and contraindications of this alternative imaging technique?

Advantages

  • Particularly useful in diagnosing or excluding chronic thromboembolic pulmonary hypertension (CTEPH) and differentiating CTEPH from other causes.

  • Differentiates CTEPH from idiopathic pulmonary artery hypertension with sensitivity 90-100% and specificity 94-100%.

  • Normal or low-probability scan essentially excludes CTEPH given sensitivity of 90-100%.

  • Considered more sensitive than for detecting CTEPH that can be treated with surgical thombebolectomy, which can affect management.

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

  • Preferred in a pregnant patient to CTA (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).

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

Disadvantages

  • The exam takes about an hour to complete, much longer than CTA. 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.

Contraindications

  • 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.

References

Brown, K. "ACR Appropriateness Criteria® pulmonary hypertension.". J Thorac Imaging. vol. 28. 2013. pp. W57-60.

http://www.acr.org/~/media/ACR/Documents/AppCriteria/Diagnostic/PulmonaryHypertension.pdf
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