Vascular Imaging

What Is the Best Initial Imaging for Suspected PAVM in an Asymptomatic Adult with HHT?

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What Is the Best Initial Imaging for Suspected PAVM in an Asymptomatic Adult with HHT?

A 38-year-old woman establishes care at your clinic. She feels perfectly healthy but is worried. Her mother was recently diagnosed with Hereditary Hemorrhagic Telangiectasia (HHT) and was found to have abnormal blood vessels in her lungs. The patient has no symptoms—no shortness of breath, no nosebleeds, no neurologic issues—but she wants to be screened. You know that pulmonary arteriovenous malformations (PAVMs) are a serious manifestation of HHT that require screening, even in asymptomatic individuals, due to the risk of stroke and brain abscess. The immediate clinical question is which imaging study to order first. This article provides a step-by-step workflow for this specific scenario, guided by the American College of Radiology (ACR) Appropriateness Criteria. For this presentation, the ACR rates `US echocardiography transthoracic with IV contrast` as Usually Appropriate.

Who Fits This Clinical Scenario for PAVM Screening?

This guidance is specifically for an asymptomatic adult patient with a known or suspected family history of Hereditary Hemorrhagic Telangiectasia (HHT) who requires initial screening for PAVMs. The key inclusion criteria are the absence of symptoms and the presence of a risk factor (family history) that raises suspicion for the condition. This is a proactive screening workflow, not a diagnostic workup for an acute problem.

It is critical to distinguish this scenario from similar but distinct clinical presentations that require different imaging pathways:

  • Symptomatic Patients: This workflow does not apply if the patient presents with symptoms such as shortness of breath (dyspnea), coughing up blood (hemoptysis), or chest pain. Those presentations suggest a potentially complicated or large PAVM and may warrant more direct anatomic imaging, like a CT angiogram, as the first step.
  • Patients with Neurologic Symptoms: If the patient has experienced a transient ischemic attack (TIA), seizure, or brain abscess, the workup is different. These are potential complications of a right-to-left shunt from a PAVM, and the imaging strategy is more urgent and may involve both brain and chest imaging concurrently.
  • Patients with Known PAVMs: This guidance is for initial screening, not for surveillance. An adult with a previously diagnosed and/or treated PAVM requires a separate follow-up imaging protocol to monitor for recurrence or the growth of new lesions.

What Diagnoses Are You Working Up in an Asymptomatic Patient with HHT Risk?

When ordering screening imaging for a patient with a family history of HHT, you are primarily investigating the presence of a right-to-left shunt, which has several potential causes.

Pulmonary Arteriovenous Malformation (PAVM): This is the principal diagnosis of concern. A PAVM is an abnormal, direct connection between a pulmonary artery and a pulmonary vein, which bypasses the lung’s capillary bed. This allows deoxygenated, unfiltered venous blood to enter the systemic circulation. Even small PAVMs can permit blood clots or bacteria to travel to the brain, causing a paradoxical embolic stroke or brain abscess. A significant percentage of individuals with HHT will develop PAVMs, making screening essential.

Intracardiac Shunt: The most common cause of a right-to-left shunt in the general population is a patent foramen ovale (PFO), an opening between the atria of the heart. An atrial septal defect (ASD) is another cause. The initial screening test, a contrast echocardiogram, is highly effective at detecting these intracardiac shunts as well. Differentiating the location of the shunt (intracardiac vs. intrapulmonary) is a key goal of the initial test.

No Abnormality: In many cases, screening will be negative, providing crucial reassurance to the patient. Ruling out a significant shunt is as important as finding one. The goal of screening is to identify the subset of at-risk individuals who require further imaging and potential treatment to prevent future complications.

Why Is Contrast Echocardiography the Recommended Initial Study for PAVM Screening?

The ACR designates `US echocardiography transthoracic with IV contrast` as Usually Appropriate for this scenario because it is a highly sensitive, non-invasive, and radiation-free method for detecting the physiologic consequence of a PAVM: a right-to-left shunt.

The “contrast” used is not iodinated dye but agitated saline. Microscopic air bubbles are injected into a peripheral vein. In a normal circulatory system, these bubbles are larger than capillaries and are filtered out by the lungs. If a right-to-left shunt exists—either in the heart or the lungs—the bubbles will bypass the capillary filter and appear in the left side of the heart, which can be visualized on the echocardiogram.

This test is ideal for screening because:

  • It answers the key physiologic question: Does a shunt exist? This is the first and most important piece of information needed.
  • It avoids radiation: With a radiation level of 0 mSv, it is a safe test for screening, particularly in younger adults who may need periodic rescreening throughout their lives.
  • It can differentiate shunt location: The timing of the bubbles’ appearance in the left atrium helps distinguish an intracardiac shunt (early appearance, within 1-3 cardiac cycles) from an intrapulmonary shunt like a PAVM (delayed appearance, typically 3-8 cardiac cycles).

Why are other studies rated lower for initial screening?

  • CTA pulmonary arteries with IV contrast: While also rated Usually Appropriate, this study is generally reserved as the next step after a shunt is detected. It provides detailed anatomy of the PAVM for treatment planning but exposes the patient to ionizing radiation (☢☢☢ 1-10 mSv) and iodinated contrast. Using it as a first-line screening tool is often considered unnecessary exposure if the physiologic screen (echo) is negative.
  • Radiography chest: This is rated Usually not appropriate. A chest X-ray has very low sensitivity for PAVMs. It may show a subtle nodule if a PAVM is large, but it will miss most lesions and cannot detect the underlying shunt physiology, making it an inadequate screening tool.

When ordering, it is crucial to specify “transthoracic echocardiogram with agitated saline contrast” or “bubble study” to ensure the correct test is performed for shunt evaluation.

What’s the Next Step After a Contrast Echocardiogram for HHT Screening?

The results of the contrast echocardiogram will direct the subsequent workflow. The decision tree is straightforward and aims to confirm and characterize any identified shunt.

If the study is POSITIVE for a right-to-left shunt:
The appearance of microbubbles in the left heart chambers confirms a shunt. If the timing is delayed (suggesting a pulmonary source), the next step is definitive anatomic imaging. The recommended study is a `CTA pulmonary arteries with IV contrast`. This CT scan will precisely locate the PAVM(s), measure the diameter of the feeding artery (a key factor in determining treatment urgency), and map the vascular anatomy for potential embolization by an interventional radiologist.

If the study is NEGATIVE for a right-to-left shunt:
A negative bubble study effectively rules out a hemodynamically significant PAVM. For an asymptomatic patient, this is a reassuring result. No immediate further imaging is required. The patient should continue to be followed clinically, with repeat screening intervals determined by established HHT guidelines, often every five to ten years, or sooner if symptoms develop.

If the study is INDETERMINATE or EQUIVOCAL:
Occasionally, an echocardiogram may be technically limited (e.g., due to poor acoustic windows). If the results are unclear, options include repeating the study at a center with advanced echocardiography expertise or proceeding to a non-contrast chest CT. A `CT chest without IV contrast` is rated Usually Appropriate and can identify most PAVMs greater than 5 mm, serving as a reasonable alternative if the echo fails.

Common Pitfalls to Avoid in Asymptomatic PAVM Screening

Navigating the screening process for HHT-associated PAVMs requires attention to detail to avoid common errors that can delay diagnosis or lead to unnecessary testing.

  • Ordering a standard echo: A transthoracic echocardiogram without agitated saline contrast is rated Usually not appropriate for this indication. It assesses cardiac structure and function but provides no information about a potential shunt. You must explicitly request the “bubble study.”
  • Overlooking bubble timing: The distinction between early-appearing bubbles (intracardiac shunt) and delayed bubbles (intrapulmonary shunt) is critical. Ensure the interpreting physician comments on this timing, as it guides whether the subsequent workup is cardiologic or pulmonologic.
  • Stopping the workup too soon: A positive bubble study is an indication for further imaging, not the final diagnosis. Treatment decisions for a PAVM cannot be made from an echocardiogram alone; a high-resolution CTA is required to define the anatomy.
  • Using CTA as the first-line screen: While effective, jumping straight to CTA in an asymptomatic patient exposes them to unnecessary radiation if a simple, safe echo study could have ruled out a shunt first.

If a significant shunt is detected on echo or a large PAVM is found on subsequent CT, the patient should be referred promptly to a multidisciplinary HHT Center of Excellence or to a pulmonologist and interventional radiologist with expertise in managing this condition.

Related ACR Topics and Tools

For further exploration of imaging decisions, the following GigHz resources provide direct access to evidence-based guidelines and practical tools.

Frequently Asked Questions

Why not just order a chest CT scan for everyone with a family history of HHT?

While a CT scan is excellent for defining the anatomy of a PAVM, it involves ionizing radiation. For an initial screening test in an asymptomatic person, the ACR recommends starting with a non-radiation alternative if one is available and effective. The contrast echocardiogram is a highly sensitive physiologic test that can rule out a significant shunt without any radiation exposure, reserving CT for those who have a positive screen.

What if my asymptomatic patient with HHT risk is pregnant?

A transthoracic echocardiogram with agitated saline contrast is safe during pregnancy as it does not use radiation or iodinated contrast. It remains the best initial screening test. CT scans should be avoided due to radiation risk to the fetus. If further anatomic imaging is absolutely necessary during pregnancy, an MRA without contrast may be considered in consultation with a radiologist and maternal-fetal medicine specialist.

Does a positive bubble study definitively mean the patient has a PAVM?

No. A positive bubble study confirms the presence of a right-to-left shunt, but it does not specify the location with 100% certainty. The most common cause of a right-to-left shunt is a patent foramen ovale (PFO) in the heart. The key diagnostic clue is the timing: bubbles appearing in the left heart after 3-8 cardiac cycles strongly suggest an intrapulmonary shunt like a PAVM, whereas bubbles appearing within 1-3 cycles suggest an intracardiac source like a PFO.

How is the ‘contrast’ in a bubble study different from CT contrast?

They are completely different. CT contrast is an iodine-based dye that can affect kidney function and cause allergic reactions. The ‘contrast’ for a bubble study is simply agitated sterile saline—salt water mixed with a small amount of air to create microbubbles. It has no effect on the kidneys, and allergic reactions are exceedingly rare.

If a patient has a family history of HHT but tested negative for the specific familial genetic mutation, do they still need screening?

This can be a complex situation best addressed with a genetic counselor or HHT specialist. If a patient has been definitively tested and confirmed not to carry the known pathogenic variant in their family, routine PAVM screening is generally not required. However, if genetic testing was inconclusive or if the patient exhibits any clinical signs of HHT (per the Curaçao criteria), clinical screening may still be recommended.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 30, 2026