What are the characteristics of an Arteriovenous Malformation (AVM) caused by Hereditary Hemorrhagic Telangiectasia (HHT) with portal hypertension?

Characteristics of HHT-Related Hepatic AVMs with Portal Hypertension

Portal hypertension in HHT results from arterioportal shunting with subsequent portal fibrosis or from nodular regenerative hyperplasia due to irregular hepatic blood flow, and occurs at a rate comparable to high-output cardiac failure (1.2 vs 1.4 per 100 person-years), accounting for approximately half of hepatic VM-associated fatalities. 1

Pathophysiologic Mechanisms of Portal Hypertension in HHT

The development of portal hypertension in HHT occurs through two distinct mechanisms:

• Arterioportal shunting creates direct connections between hepatic arteries and portal veins, leading to increased portal venous pressure and subsequent development of portal fibrosis 1
• Nodular regenerative hyperplasia (NRH) develops from heterogeneous liver blood perfusion caused by the vascular malformations, creating architectural distortion that impedes portal flow 1

Anatomic and Vascular Characteristics

Hepatic VMs in HHT involve the liver diffusely and evolve along a continuum from small telangiectases to large arteriovenous malformations, with 21% showing increased size and complexity over median 44-month follow-up 1

The vascular architecture demonstrates:

• Three concomitant shunting patterns: hepatic artery to portal vein (arterioportal), hepatic artery to hepatic vein (arteriovenous), and portal vein to hepatic vein (portovenous) 1
• Markedly dilated hepatic artery with diameter >6 mm in advanced cases (Doppler grade 2-4) 1
• Complex flow abnormalities in both arterial and venous systems, with peak flow velocity >80 cm/sec and resistivity index <0.55 1
• Diffuse intrahepatic hypervascularization creating heterogeneous hepatic enhancement on imaging 1, 2

Clinical Presentation and Complications

Portal hypertension in HHT presents with distinct features compared to cirrhotic portal hypertension:

• Preserved liver synthetic function and normal platelet counts despite portal hypertension, because these patients lack cirrhosis and do not develop liver insufficiency 1
• Variceal bleeding can occur, but gastrointestinal bleeding is more commonly due to GI telangiectasias than varices 1
• Ascites as the most common presentation of portal hypertension, though less frequent than in cirrhotic patients 1
• Anicteric cholestasis in one-third of patients, with degree correlating to VM severity 1

Associated Hepatic Parenchymal Changes

The liver may appear nodular and is frequently misinterpreted as cirrhosis, but represents "pseudocirrhosis" from fibrosis around abnormal vessels, NRH, and portal hypertension without true cirrhotic architecture 1

Key parenchymal features include:

• Focal nodular hyperplasia (FNH) with 100-fold greater prevalence than general population (2.9% vs 0.03%) 1
• Nodular regenerative hyperplasia from irregular perfusion patterns 1
• Fibrous tissue expansion in portal areas without complete regenerative nodules characteristic of cirrhosis 1

Diagnostic Imaging Characteristics

Doppler ultrasound serves as first-line diagnostic imaging and provides severity grading (0.5-4) that correlates with clinical outcome 1

Portal hypertension-specific findings include:

• Grade 3-4 disease: Abnormal hepatic and/or portal vein flow with marked flow abnormalities, and dilatation of hepatic/portal veins indicating shunt decompensation 1
• Enlarged hepatic artery (>6 mm) with both extra- and intrahepatic dilatation 1
• Heterogeneous hepatic enhancement on multiphase CT from diffuse telangiectases 1

Epidemiologic and Genetic Factors

Portal hypertension risk varies by genotype and demographics:

• HHT2 (ALK-1 mutations) shows greater frequency of hepatic VMs and symptomatic liver disease compared to HHT1 (endoglin mutations) 1
• Female predominance with male:female ratio of 1:2 to 1:4.5 for both asymptomatic and symptomatic hepatic VMs 1
• Mean age of presentation is 52 years, with symptoms appearing around age 30 1

Critical Clinical Pitfalls

Liver biopsy must be strictly avoided in HHT patients due to high hemorrhage risk, as it is often misinterpreted, provides less information than imaging, and is dangerous 1, 3

Additional important caveats:

• Do not misdiagnose as hepatocellular carcinoma: FNH masses in nodular-appearing liver can be confused with HCC, which has not been described in HHT 1
• Recognize preserved synthetic function: Normal liver function tests and platelet counts despite portal hypertension distinguish HHT from cirrhosis 1
• Atrial fibrillation occurs at 1.6 per 100 person-years in patients with chronic cardiac overload from liver VMs and should be approached with special caution 1

Rare Catastrophic Complications

Biliary ischemia from arteriovenous shunting can progress to "hepatic disintegration"—bile duct and liver necrosis presenting with sudden right upper quadrant pain, cholangitis, sepsis, and/or liver hemorrhage 1

Other uncommon presentations include:

• Hepatic encephalopathy from portovenous shunting 1
• Mesenteric angina from arterial "steal" through pancreaticoduodenal arteries 1