A hepatic arteriovenous malformation (AVM) is an abnormal tangle of blood vessels in the liver. It creates a direct connection between an artery and a vein, bypassing the normal capillary network. This disruption diverts high-pressure arterial blood directly into a low-pressure vein, which is not built to handle the force. This short circuit alters blood distribution and can deprive surrounding liver tissue of adequate oxygen.
Causes of Hepatic AVMs
The origins of hepatic AVMs are either congenital or acquired. Most are congenital, meaning they are present at birth due to an error in blood vessel development while in the womb. The specific trigger for this developmental mistake is frequently unknown, and it is not considered a condition that is inherited or results from maternal actions during pregnancy.
A smaller number of hepatic AVMs are acquired after birth. These can develop from direct physical injury to the liver, such as from an accident. They may also arise following medical procedures like liver biopsies and surgeries, or in association with liver tumors. In these instances, the injury or procedure disrupts the normal vessel structure, leading to an abnormal artery-to-vein connection.
Recognizing Symptoms
Many individuals with small hepatic AVMs experience no symptoms, and the condition is often found by chance during medical imaging for other issues. When symptoms do appear, they differ significantly based on the AVM’s size and how much blood it shunts away from normal circulation. The presentation varies between infants and adults.
In infants, a large hepatic AVM can cause high-output heart failure. Signs of this condition include difficulty breathing, poor feeding, and failure to grow and gain weight at a normal rate.
Adults with symptoms may experience abdominal pain, often in the upper right quadrant where the liver is located. Other signs include a palpable mass or a distinct vibration over the liver. A physician might also detect an abdominal bruit, which is a whooshing sound from turbulent blood flow that can be heard with a stethoscope.
Diagnostic Process
Diagnosing a hepatic AVM begins with non-invasive imaging. A Doppler ultrasound is often the first step, as it can visualize blood flow in the liver and detect the high-velocity patterns characteristic of an AVM.
If an ultrasound suggests an AVM, more detailed imaging is required. A multiphase computed tomography (CT) scan or CT angiography (CTA) provides cross-sectional images that map the liver’s vascular system. Magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) can also generate high-resolution images of the blood vessels without using ionizing radiation.
The definitive diagnostic method for confirming an AVM and planning treatment is catheter-based angiography. During this procedure, a catheter is guided through blood vessels to the liver. A special dye is injected, making the vessels visible on X-ray and providing a real-time map of the AVM’s structure and blood flow.
Treatment Options
Managing a hepatic AVM depends on its size, location, and whether it causes symptoms. For small, asymptomatic AVMs, a watchful waiting approach with regular imaging follow-up may be sufficient. This strategy avoids the risks of intervention when the AVM is not causing harm.
For symptomatic or large AVMs, the most common treatment is transarterial embolization. In this minimally invasive procedure, an interventional radiologist guides a catheter to the AVM. Tiny particles, medical glue, or small metal coils are then used to block the abnormal connection, which stops the blood shunting and alleviates symptoms.
If embolization is not feasible due to the AVM’s size or complexity, surgery may be an option. Surgical resection involves removing the portion of the liver containing the AVM. This approach can be curative but is more invasive and has a longer recovery, so it is reserved for AVMs that can be removed without compromising liver function.
For the most severe cases, liver transplantation may be the only option. This is considered when an AVM is too large for other treatments or has caused irreversible liver damage. The procedure involves replacing the entire diseased liver with a healthy donor liver, which provides a definitive cure.
Associated Health Complications
A hepatic AVM can alter the body’s circulation and lead to serious health problems. One primary complication is high-output cardiac failure. The direct shunting of blood from an artery to a vein forces a large volume of blood to return to the heart quickly, overworking the heart muscle as it tries to keep up.
Another complication is portal hypertension, which is high blood pressure in the portal vein system that carries blood to the liver. The increased flow from the AVM can back up into this system. This can lead to fluid accumulation in the abdomen (ascites) and swollen, bleeding-prone veins in the esophagus and stomach.
The diversion of arterial blood can also cause biliary ischemia. Bile ducts, which transport bile from the liver, get their blood from the hepatic artery. When an AVM shunts blood away, the bile ducts can be deprived of oxygen, leading to damage or strictures that impair their function.