Vascular Imaging

What Imaging Is Best for Surveillance After PAVM Embolization? An ACR Workflow

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What Imaging Is Best for Surveillance After PAVM Embolization? An ACR Workflow

A 48-year-old patient establishes care at your practice. Reviewing their records, you note they underwent a successful coil embolization of a large pulmonary arteriovenous malformation (PAVM) six years ago and have been lost to follow-up since. They are currently asymptomatic but are concerned about the status of the treated lesion and want to know if they need ongoing monitoring. You need to decide on the most appropriate imaging study for surveillance in this specific clinical context. This article details the clinical workflow for this exact scenario, focusing on the rationale behind study selection and the downstream decision-making process.

Based on the American College of Radiology (ACR) Appropriateness Criteria, a transthoracic echocardiogram with intravenous contrast (a “bubble study”) is rated Usually Appropriate as a primary surveillance tool for a previously treated PAVM.

Who Fits This Clinical Scenario for PAVM Surveillance?

This guidance is specifically for an adult patient with a known, previously treated pulmonary arteriovenous malformation, most commonly via transcatheter embolization. The clinical question is one of routine surveillance in an asymptomatic or clinically stable individual. The goal is to assess for the long-term success of the embolization and to monitor for any changes that may require further intervention.

This workflow is distinct from other similar, but clinically different, presentations:

  • Exclusion 1: New Neurologic Symptoms. If a patient (with or without a known PAVM) presents with a new transient ischemic attack, seizure, or signs of a brain abscess, the workup is different. That scenario requires an urgent evaluation for an active, significant right-to-left shunt.
  • Exclusion 2: New Pulmonary Symptoms. If a patient presents with new-onset shortness of breath, hemoptysis, or has a known history of Hereditary Hemorrhagic Telangiectasia (HHT) with worsening symptoms, this constitutes a diagnostic workup, not routine surveillance.
  • Exclusion 3: Initial Screening. This guidance does not apply to asymptomatic patients being screened for PAVMs for the first time due to a family history of HHT or an incidental finding on a chest radiograph.

The focus here is strictly on long-term, scheduled follow-up after a definitive treatment has already been performed.

What Are We Looking For in Post-Embolization PAVM Surveillance?

In surveillance imaging for a treated PAVM, the “differential diagnosis” is a specific set of potential outcomes related to the prior intervention and the underlying disease process. The primary goal is to detect any recurrent or new right-to-left shunting, which poses a risk for paradoxical embolism and subsequent stroke or brain abscess.

Recanalization of the Treated PAVM. This is the most critical finding to identify. Over time, the embolization coils or plugs can compact, or the vessel can remodel around the embolic material, creating a new channel for blood flow. This re-establishes the right-to-left shunt and restores the risk of paradoxical embolism.

Growth of Previously Small, Untreated PAVMs. Many patients with PAVMs, particularly those with HHT, have multiple lesions. Interventional procedures typically target the largest malformations with feeding arteries of 3 mm or greater. Smaller, untreated PAVMs can enlarge over time, eventually reaching a size that becomes hemodynamically significant and warrants treatment.

Development of New PAVMs. The underlying pathophysiology, especially in HHT, can lead to the formation of entirely new PAVMs in different locations within the lungs. Surveillance imaging is designed to detect these new lesions before they become large enough to cause symptoms or complications.

Stable Post-Treatment Appearance. The ideal and most common finding is a durably occluded PAVM with no evidence of recanalization, and no new or enlarging lesions elsewhere. This confirms the success of the initial treatment and allows for continued, less frequent monitoring.

Why Is Contrast Echocardiography a Recommended Study for PAVM Follow-Up?

For routine surveillance of a treated PAVM, the ACR panel rates US echocardiography transthoracic with IV contrast as Usually Appropriate. This procedure, commonly known as a “bubble study,” is a functional test designed to detect the presence of a right-to-left shunt, which is the core physiological problem.

The rationale for its high rating is based on several factors:

  • High Sensitivity for Shunting: The test involves injecting agitated saline (containing microbubbles too large to pass through the pulmonary capillary bed) into a peripheral vein. If an intrapulmonary shunt exists, these microbubbles will bypass the capillaries and appear in the left atrium and ventricle within 3 to 5 cardiac cycles. This makes it a highly sensitive method for detecting the presence of a shunt, which is the primary surveillance question.
  • No Ionizing Radiation: A key advantage for long-term, repeated surveillance is the complete absence of radiation exposure (Adult RRL=O 0 mSv). This is particularly important in patients with HHT who may require lifelong monitoring.
  • Non-Invasive and Widely Available: Transthoracic echocardiography is a readily accessible, low-risk procedure that does not require iodinated contrast, making it safe for patients with renal insufficiency.

How do alternative studies compare for this specific scenario?

  • CTA pulmonary arteries with IV contrast is also rated Usually Appropriate. It provides superb anatomical detail of the pulmonary vasculature, allowing direct visualization of a recanalized vessel or a new PAVM. However, it involves a notable dose of ionizing radiation (Adult RRL=☢☢☢ 1-10 mSv). Therefore, while it is the definitive study for anatomical assessment and pre-procedural planning, it is often reserved as the second-line test to be used after a bubble study has confirmed the presence of a shunt.
  • Radiography chest is rated Usually not appropriate. A standard chest X-ray has very poor sensitivity for detecting PAVMs or assessing the status of an embolization. It cannot detect shunting and will miss many anatomically significant lesions, providing a false sense of security.

When ordering the recommended study, it is crucial to specify “with bubble study” or “for right-to-left shunt evaluation” to ensure the correct protocol is performed.

Downstream Workflow: What to Do After a PAVM Surveillance Echocardiogram

The results of the surveillance bubble study will guide the next steps in the patient’s management plan. The workflow is a branching pathway based on whether a shunt is detected.

If the bubble study is POSITIVE (shunt detected):
The presence of microbubbles in the left heart confirms a recurrent or new intrapulmonary shunt. This finding necessitates further investigation to define the anatomy of the shunt.

  • Next Step: Order a CTA pulmonary arteries with IV contrast. This study will pinpoint the location and size of the culprit vessel(s)—whether it is the original PAVM that has recanalized, a previously known small PAVM that has grown, or a newly developed lesion.
  • Subsequent Action: Based on the CTA findings, a referral to an Interventional Radiologist is warranted to discuss the risks and benefits of repeat embolization.

If the bubble study is NEGATIVE (no shunt detected):
This is a reassuring result, indicating the prior treatment remains effective and no new significant shunts have developed.

  • Next Step: No immediate further imaging is required.
  • Subsequent Action: The patient can continue routine surveillance. The interval for the next follow-up study is typically guided by international HHT guidelines or institutional protocol, often ranging from 3 to 5 years if the patient remains stable and asymptomatic.

If the bubble study is INDETERMINATE or EQUIVOCAL:
Occasionally, the study may be technically limited. In such cases, or if clinical suspicion remains high despite a negative study, an alternative imaging modality is needed.

  • Next Step: Consider a non-radiation alternative like MRA pulmonary arteries without and with IV contrast (Usually Appropriate) or proceed directly to a low-dose protocol CTA chest with IV contrast (Usually Appropriate). The choice depends on institutional preference and patient-specific factors like contraindications to MRI or iodinated contrast.

Pitfalls to Avoid (and When to Get Help)

When managing surveillance for treated PAVMs, several common pitfalls can compromise patient care.

  • Ordering a standard TTE: Simply ordering a “transthoracic echocardiogram” without specifying “with bubble study” will result in the wrong test being performed, as a standard echo cannot detect an intrapulmonary shunt.
  • Relying on chest X-ray: Using a chest radiograph for surveillance is inadequate due to its low sensitivity and should be avoided.
  • Ignoring small shunts: Even a “small” shunt on a bubble study warrants further anatomical evaluation with CTA, as the size of the shunt on echo does not always correlate with the size of the feeding artery or the risk of stroke.
  • Delaying follow-up: Extending surveillance intervals beyond recommended guidelines (typically not exceeding 5 years in stable patients) can lead to a missed opportunity to detect and treat a recurrent shunt before a complication occurs.

If a new or recurrent shunt is identified on any imaging, prompt consultation with an Interventional Radiologist or a pulmonologist at a center with HHT expertise is the appropriate next step.

Related ACR Topics and Tools

For a comprehensive overview of all clinical variants related to Pulmonary Arteriovenous Malformation, please consult our parent topic guide. Additional tools are available to assist with imaging decisions and patient communication.

Frequently Asked Questions

How often should surveillance imaging be performed after PAVM embolization?

The optimal interval is not universally defined, but expert guidelines, such as those for Hereditary Hemorrhagic Telangiectasia (HHT), often suggest a post-procedural check at 6-12 months, followed by surveillance every 3-5 years if the patient remains stable and asymptomatic. The frequency may be increased if there is evidence of a persistent or recurrent shunt.

If a contrast echocardiogram is positive, is CTA always the next step?

Yes, in almost all cases. The contrast echocardiogram is a functional test that confirms a right-to-left shunt but provides no anatomical information. A CTA of the pulmonary arteries is necessary to identify the location, size, and anatomy of the vessel causing the shunt, which is essential for planning any potential re-intervention with Interventional Radiology.

Can MRI/MRA be used for PAVM surveillance instead of CT?

Yes, MRA of the pulmonary arteries with and without IV contrast is also rated ‘Usually Appropriate’ by the ACR. It is an excellent alternative that avoids ionizing radiation. The choice between CTA and MRA after a positive bubble study often depends on institutional expertise, scanner availability, and patient factors such as claustrophobia or contraindications to gadolinium-based contrast agents.

What if the patient is pregnant and due for surveillance?

This is a complex scenario requiring multidisciplinary consultation. A transthoracic echocardiogram with a bubble study is generally considered safe during pregnancy as it avoids radiation. If a significant shunt is detected, the risks and benefits of proceeding with further imaging like a non-contrast MRA or deferring intervention until after delivery must be carefully weighed by the patient’s cardiology, pulmonology, and obstetrics teams.

Does the type of embolic device used for the original treatment affect the choice of surveillance imaging?

Generally, no. The choice of surveillance imaging—starting with a functional test like a bubble study—is independent of whether coils, plugs, or other devices were used. However, the appearance of these devices on subsequent CTA or MRA will differ, and the radiologist interpreting the anatomical study should be aware of the patient’s procedural history.

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