Veterinary Guide to Canine Hepatic Arteriovenous Malformations (AVMs) 2025 🐶🩺

By Dr. Duncan Houston BVSc

🧬 What Is a Hepatic AVM?

A hepatic arteriovenous malformation (AVM) or fistula occurs when high-pressure arteries directly connect to low-pressure portal veins in the liver, bypassing the capillaries. The result is turbulent flow, portal hypertension, ascites, and often acquired portosystemic shunts.

Causation: Congenital vs Acquired

• Congenital AVMs are developmental vascular malformations—often multiple communications between hepatic artery and portal vein branches. Dogs may present young with signs of liver dysfunction.
• Acquired fistulas result from liver trauma, biopsies, or develop within tumors—less common but still significant.

👥 Who’s Affected?

• Any breed or age—congenital AVMs reported in young dogs.
• Acquired cases follow trauma or neoplastic processes, generally in adults.

⚠️ Clinical Signs

• Abdominal distension/ascites due to portal hypertension.
• Signs of hepatic encephalopathy—lethargy, disorientation, seizures—as toxins bypass liver filtration.
• Gastrointestinal symptoms—vomiting or diarrhea, possibly with blood.
• A liver bruit or murmur—turbulent intraparenchymal flow.

🔍 Diagnostic Approach

1. Physical exam & labwork: CBC/chem may show elevated liver enzymes, hypoalbuminemia, coagulopathy. Schistocytes may appear on blood smear.
2. Ultrasound with Doppler: Detects arterialized portal flow, turbulent intrahepatic channels.
3. CT/angiography: Gold standard to detail nidus, feeding/draining vessels.
4. Liver biopsy or FNA: Confirm histopathology—evaluate fibrosis, inflammation, or tumor presence.
5. Contrast studies: Portal pressure measurement and imaging for acquired shunts.

🛠️ Treatment Options

1. Interventional Radiology (Embolization)

• Catheter-based embolization of nidus is minimally invasive—reduces shunting.
• Materials: coils, vascular plugs to occlude abnormal channels.
• Requires advanced imaging and specialist care.

2. Surgical Management

• Direct ligation or vessel resection—possible in select, well-localized cases.
• Surgical risk high; multifocal congenital AVMs often not fully operable.

3. Medical/Supportive Care

• Manage ascites with low-sodium diets and diuretics.
• Address hepatic encephalopathy: lactulose, antibiotics (neomycin/metronidazole), protein restriction.
• Manage coagulopathy with vitamin K, transfusions if needed.

📈 Prognosis

• Guarded if untreated—complications from portal hypertension and HE are serious.
• Better outcomes with successful embolization or surgical correction—minimized portal pressures.
• Congenital multifocal AVMs harder to correct and more likely to require long-term supportive care.

📱 Ask A Vet Telehealth Support

• 📸 Upload ultrasound or CT images and labs for specialist interpretation.
• 🔔 Treatment reminders—for embolization prep, diet, meds, follow-up imaging.
• 🩺 Virtual check-ins to assess ascites, neurologic signs, and quality of life.

🎓 Case Spotlight: “Cookie” the French Bulldog

Cookie presented with abdominal fluid, poor energy, and diarrhea. Ultrasound revealed turbulent flow; CT confirmed congenital intrahepatic AVM. Interventional embolization was performed. Ask A Vet coordinated imaging transfer, post-op follow-ups, diuretic management, and diet. One year later, ascites resolved, and Cookie has returned to playful behavior 🐾.

🔚 Key Takeaways

1. Hepatic AVMs are rare vascular anomalies that cause portal hypertension and encephalopathy.
2. Diagnosis requires Doppler ultrasound and CT angiography; biopsy confirms tissue changes.
3. Interventional embolization offers the best chance for correction; surgery or supportive care follows.
4. Without intervention, the prognosis is guarded; treated dogs may enjoy good quality of life.
5. Ask A Vet telehealth helps with diagnostics, treatment coordination, follow-up, and home care monitoring 📲🐾

Dr Duncan Houston BVSc, founder of Ask A Vet. Download the Ask A Vet app for expert telehealth: imaging review, interventional planning, embolization coordination, post-treatment monitoring, and ongoing support for dogs with hepatic vascular anomalies 🐶📲