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Visceral AVMs: How HHT Affects Your Organs

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Visceral AVMs in HHT are abnormal connections between arteries and veins in the lungs, liver, and brain. They bypass normal capillary filters, potentially causing strokes, heart failure, or internal bleeding. Proactive screening is vital because these malformations are often silent until a crisis occurs.

Key Takeaways

  • • Visceral AVMs in HHT create dangerous high-pressure short circuits in internal organs by bypassing normal capillary beds.
  • • Lung AVMs skip the lung's filtering process, increasing the risk of stroke, brain infections, and low blood oxygen.
  • • Liver AVMs force the heart to work much harder, which can eventually lead to high-output heart failure.
  • • Brain AVMs affect about 10% of HHT patients and carry a significant risk of causing a hemorrhagic stroke if they rupture.
  • • Because visceral AVMs are often silent, proactive screenings like bubble studies and MRIs are essential to detect them before a crisis.

In HHT, the most serious health risks often come from visceral arteriovenous malformations (AVMs). These are abnormal connections between arteries and veins in your internal organs [1][2].

To understand why these are dangerous, think of your blood vessels like a highway system. In a healthy body, blood must pass through a “toll booth” of tiny capillaries before moving from an artery to a vein. These capillaries slow down the blood flow and act as a filter. In an AVM, the toll booth is missing. The blood “shunts” directly from a high-pressure artery into a low-pressure vein [1][2]. This creates a high-pressure short circuit that can affect the organ and your entire circulatory system [3][4].

Lungs (Pulmonary AVMs)

When an AVM is in the lung, it creates a right-to-left shunt [5][1]. This means blood skips the “filter” of the lung’s capillary bed.

  • Paradoxical Embolism: Normally, the lungs filter out tiny blood clots or bacteria. Because of the shunt, these can pass directly to the brain, potentially causing a stroke or a brain abscess (a serious infection) [2][6][7].
  • Hypoxemia: Since the blood skips the part of the lung where it picks up oxygen, you may have low blood oxygen levels (hypoxemia), which can cause shortness of breath or fatigue [5][7].

Liver (Hepatic AVMs)

Liver AVMs are very common in HHT, but they act differently than those in the lungs [8][4].

  • High-Output Heart Failure: Because blood is rushing through the liver “short circuit” so fast, your heart has to work much harder to keep up. Over time, this extra work can lead to high-output heart failure [4][9].
  • Portal Hypertension: The abnormal pressure can cause high blood pressure in the veins of the liver, leading to complications similar to liver cirrhosis [8][10].
  • Biliary Issues: The shunts can sometimes “steal” blood away from the bile ducts, causing damage or pain in the liver [11][12].

Brain (Cerebral AVMs)

Cerebral AVMs are present in about 10% of people with HHT [13].

  • Hemorrhage: The main risk is that these fragile, high-pressure vessels could rupture, causing bleeding in the brain (a hemorrhagic stroke) [13][14].
  • Silent Nature: Many brain AVMs never cause symptoms until they bleed, which is why screening with an MRI is often recommended [15][16].

Why Proactive Screening is Vital

Visceral AVMs are often called “silent” because your body is very good at compensating for them [4][17]. You might feel perfectly fine even while a lung AVM is putting you at risk for a stroke.

Specialized screenings—like a bubble study (an ultrasound of the heart with salt water bubbles) for the lungs or an MRI for the brain—are designed to find these “short circuits” before they cause a crisis [15][18][16]. Identifying them early allows your medical team to monitor them or treat them with embolization (a procedure to block off the abnormal vessel) before complications occur [15][18].

Frequently Asked Questions

Why are visceral AVMs dangerous in HHT?
Visceral AVMs create a high-pressure short circuit between arteries and veins, bypassing the tiny capillaries that normally slow down and filter blood. This abnormal blood flow can strain the heart and allow unfiltered blood clots or bacteria to travel throughout the body.
What happens if I have an AVM in my lungs?
Lung AVMs allow blood to skip the filtering process, increasing the risk of strokes or brain infections from small clots and bacteria. They can also cause low blood oxygen levels, which may lead to shortness of breath or fatigue during physical activity.
How do liver AVMs affect the heart?
Blood rushes through liver AVMs very quickly, forcing your heart to work much harder to keep up. Over time, this constant extra strain can lead to a condition called high-output heart failure.
Why do I need screening for AVMs if I feel perfectly fine?
Visceral AVMs are often silent, meaning your body compensates for them well before they cause noticeable symptoms. Proactive screenings, like a bubble study or MRI, help doctors find these malformations early so they can be monitored or treated before a complication like a stroke happens.
How are visceral AVMs treated?
When an AVM needs treatment, doctors often use a procedure called embolization to block off the abnormal blood vessel. Depending on the location and severity, treatments like surgery or radiation may also be considered, especially for brain AVMs.

Questions for Your Doctor

  • • Which organs have we screened so far, and what are the results for each?
  • • If I have silent AVMs, how often do they need to be re-imaged to check for growth?
  • • Do I need to take antibiotics before dental work to protect my brain from infections related to lung shunts?
  • • Is my heart showing any signs of strain from blood shunting in my liver?
  • • If a brain AVM is found, do the risks of treatment (like surgery or radiation) outweigh the risks of leaving it alone?

Questions for You

  • • Do I ever feel short of breath during activities that used to be easy for me?
  • • Have I noticed any bluish tint to my lips or fingertips, especially during exercise? (This could be a sign of low oxygen).
  • • Have I had any "migraine-like" headaches or sudden, brief neurological symptoms?

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References

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This page provides educational information about HHT and visceral AVMs. It is not intended as medical advice. Always consult your healthcare provider or an HHT specialist regarding your specific screening and treatment needs.

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