Pulmonary AVMs and HHT

What is HHT?

Hereditary hemorrhagic telangiectasia is an autosomal dominant genetic vascular disorder that affects roughly 1 in 5,000 people worldwide.¹ It is caused most often by mutations in the ENG (endoglin), ACVRL1 (ALK1), or SMAD4 genes — all part of the TGF-β/BMP9 signaling pathway that maintains normal blood vessel architecture. The result is fragile, abnormal blood vessels — telangiectasias on the skin and mucosa, and arteriovenous malformations in the lungs, liver, brain, and gastrointestinal tract.

Diagnosis is made clinically by the Curaçao criteria — recurrent epistaxis (nosebleeds), mucocutaneous telangiectasias, visceral AVMs, and a first-degree relative with HHT — or by genetic testing. Three or four criteria establish a definite diagnosis. Despite affecting a large population, HHT is widely under-diagnosed: most patients live with years of nosebleeds and unexplained migraines or strokes before the syndrome is recognized.²

Why pulmonary AVMs matter

Roughly 30–50% of HHT patients have at least one pulmonary arteriovenous malformation.² A PAVM is a direct connection between a pulmonary artery and pulmonary vein that bypasses the normal capillary network of the lungs. That capillary bed is more than a gas exchanger — it filters small clots, bacteria, and air bubbles from the venous circulation before they reach the brain. When a PAVM bypasses that filter, the consequences can be severe:

• Paradoxical stroke — small venous clots reach the cerebral arteries, causing ischemic stroke even in young patients
• Brain abscess — venous bacteria seed the brain, a feared and highly morbid complication
• Hypoxia and exercise intolerance — significant right-to-left shunting drops oxygen saturation
• Massive hemoptysis or hemothorax — rare, but life-threatening, when a PAVM ruptures into the airway or chest cavity
• Migraine with aura — substantially more common in PAVM patients and often improves dramatically after treatment

For these reasons, the Second International HHT Guidelines (2020) recommend embolization of any PAVM with a feeding artery 2–3 mm or larger, regardless of symptoms.³

Screening and diagnosis

The standard screening test is transthoracic contrast echocardiography (TTCE), often called the “bubble study.” Agitated saline is injected into a peripheral vein, and an echocardiogram watches for bubbles to appear on the left side of the heart. A delayed appearance after several heartbeats indicates a right-to-left shunt — most commonly a PAVM. Confirmation is by thin-section contrast-enhanced chest CT angiography, which maps every PAVM and measures the feeding-artery diameter that determines whether each lesion needs treatment. Adults with HHT should be screened at diagnosis; children should be screened in adolescence and again as adults.³

PAVM embolization

Embolization closes the feeding artery just before it enters the venous sac. Modern devices include detachable platinum coils, microvascular plugs (MVP), Amplatzer Vascular Plug (AVP) devices, and hydrogel-coated coils. Long-term studies report durable occlusion in approximately 85–95% of treated PAVMs at 5+ years, with reperfusion of treated lesions in roughly 10–15% — an entirely manageable outcome with surveillance imaging and re-treatment when needed.⁴ The procedure is performed through a small femoral or radial artery puncture under sedation, takes 1–3 hours, and most patients are discharged the same day or after one night.

When to treat

Modern Society for Vascular Surgery (SVS) guidelines have shifted toward earlier intervention than in the past:⁵

• Splenic artery aneurysm — repair at 3 cm or larger; smaller in pregnancy, women of childbearing age, portal hypertension, or transplant candidates
• Hepatic, celiac, and superior mesenteric artery aneurysms — generally repair at 2 cm or larger
• Pancreaticoduodenal and gastroduodenal aneurysms — repair regardless of size, given high rupture risk
• Renal artery aneurysm — repair at 2 cm or larger, with smaller thresholds in pregnancy or uncontrolled hypertension
• Any pseudoaneurysm — treat regardless of size

Embolization approach

The embolic strategy depends on the aneurysm’s geometry and the importance of preserving the parent vessel. Sac packing with detachable coils is straightforward when the aneurysm has a narrow neck. The isolation technique (sometimes called front-and-back-door embolization) closes the inflow and outflow vessels and is appropriate when the parent artery has good collateral circulation — the spleen, for example, tolerates splenic artery occlusion well. When the parent vessel must be preserved (renal, hepatic, mesenteric arteries), a covered stent excludes the aneurysm while maintaining flow. Liquid embolics (n-BCA glue, Onyx) are useful for irregular geometry. Modern series report technical success above 95% with major complication rates under 5%.⁶

Who performs embolization

Embolization is performed by interventional radiologists and, for many visceral lesions, by vascular surgeons working in hybrid operating rooms. The common thread is image-guided technique: detailed pre-procedure mapping, precise catheter navigation, and selective embolization. At Florida Interventional Specialists, every embolization is performed under live imaging guidance and integrated with the patient’s broader specialty care — pulmonology and HHT specialty teams for PAVMs, vascular surgery and hepatology for visceral aneurysms.

Frequently asked questions

Why do PAVMs need to be treated even without symptoms?

Because the lifetime risk of paradoxical stroke and brain abscess is meaningful, even in patients who feel well. The 2020 international guidelines recommend embolization of any PAVM with a feeding artery 2–3 mm or larger, regardless of symptoms.

What is a bubble study?

It’s the standard screening test for PAVMs. Agitated saline is injected into a vein, and an echocardiogram watches for bubbles on the left side of the heart. Their delayed appearance suggests a right-to-left shunt, prompting confirmatory CT angiography.

Will I need repeat embolization?

Some HHT patients return for additional sessions as new PAVMs develop or treated lesions reperfuse. This is expected and is part of long-term care. Surveillance imaging at 1 year and every 3–5 years catches these changes early.

When should a splenic artery aneurysm be repaired?

SVS guidelines recommend repair at 3 cm or larger, and at smaller sizes during pregnancy, in women of childbearing age, portal hypertension, transplant candidates, or any pseudoaneurysm.

Is embolization painful?

The procedure is performed under sedation or general anesthesia. Post-embolization syndrome — mild fever, fatigue, and discomfort over the treated organ for several days — is common after splenic, hepatic, or renal embolization and is managed with anti-inflammatory medication.

References

1. Kjeldsen AD, Vase P, Green A. Hereditary haemorrhagic telangiectasia: a population-based study of prevalence and mortality in Danish patients. J Intern Med. 1999;245(1):31–39.
2. Shovlin CL. Pulmonary arteriovenous malformations. Am J Respir Crit Care Med. 2014;190(11):1217–1228.
3. Faughnan ME, Mager JJ, Hetts SW, et al. Second International Guidelines for the Diagnosis and Management of Hereditary Hemorrhagic Telangiectasia. Ann Intern Med. 2020;173(12):989–1001.
4. Hsu CC, Kwak GH, Pierce DB, et al. Long-term outcomes of pulmonary arteriovenous malformation embolization in adults: a systematic review and meta-analysis. J Vasc Interv Radiol. 2020;31(11):1746–1759.e2.
5. Chaer RA, Abularrage CJ, Coleman DM, et al. The Society for Vascular Surgery clinical practice guidelines on the management of visceral aneurysms. J Vasc Surg. 2020;72(1S):3S–39S.
6. Barrionuevo P, Malas MB, Nejim B, et al. A systematic review and meta-analysis of the management of visceral artery aneurysms. J Vasc Surg. 2019;70(5):1694–1699.