How does Budd-Chiari syndrome cause portal hypertension?

How Budd-Chiari Syndrome Causes Portal Hypertension

Budd-Chiari syndrome causes portal hypertension through obstruction of hepatic venous outflow, which leads to increased sinusoidal pressure that backs up into the portal venous system. 1

Pathophysiological Mechanism

The development of portal hypertension in Budd-Chiari syndrome follows a specific sequence of events:

Primary Obstruction and Immediate Consequences

• Hepatic venous outflow obstruction can occur anywhere from the small hepatic venules to the entrance of the inferior vena cava into the right atrium 1
• This obstruction blocks the normal drainage of blood from the liver, causing blood to accumulate within the hepatic sinusoids 1
• Sinusoidal congestion develops as blood cannot exit the liver through the normal venous pathways 1, 2, 3

Pressure Transmission and Portal Hypertension

• The increased pressure in the hepatic sinusoids directly transmits backward into the portal venous system 3
• This creates increased hepatic sinusoidal pressure, which is the fundamental mechanism driving portal hypertension in this condition 3
• Portal hypertension follows the hydraulic principle where pressure equals resistance times flow—the obstruction creates massive resistance to outflow 4

Progressive Hepatic Injury

The sustained venous congestion triggers a cascade of liver damage:

• Hepatic ischemia develops because the congested sinusoids impair oxygen delivery to hepatocytes 1
• Hepatocellular necrosis occurs, particularly in centrilobular regions where congestion is most severe 1, 5
• Over time, this progresses to centrilobular fibrosis, nodular regenerative hyperplasia, and potentially cirrhosis 1
• Once cirrhosis develops, it adds a second mechanism of portal hypertension through increased intrahepatic resistance 1

Anatomic Patterns of Obstruction

The location of obstruction influences the severity and pattern of portal hypertension:

• Hepatic vein obstruction alone occurs in approximately 20-30% of cases 6, 5
• Inferior vena cava obstruction (with or without hepatic vein involvement) occurs in 57-60% of cases 6, 5
• Combined hepatic vein and IVC obstruction represents the most severe form, occurring in approximately 40% of cases 5
• Membranous obstruction represents a distinct subtype seen in 25-37% of cases 6, 5

Clinical Manifestations of Portal Hypertension

The portal hypertension in Budd-Chiari syndrome manifests through typical complications:

• Intractable ascites develops in 76-83% of patients and is often the presenting feature 1, 6
• Esophageal varices occur in approximately 56% of patients 6
• Gastrointestinal bleeding from varices occurs in 22-31% of cases 1, 6
• Splenomegaly and hepatomegaly are common physical findings reflecting the portal hypertension 5

Important Clinical Distinction

A critical point is that Budd-Chiari syndrome represents post-sinusoidal (post-hepatic) portal hypertension, distinguishing it from cirrhotic portal hypertension which is primarily sinusoidal 7. This distinction is important because:

• The liver parenchyma may initially be relatively preserved despite severe portal hypertension 7
• Interventions that restore hepatic venous drainage (angioplasty, TIPS) can be more effective than in cirrhotic portal hypertension 7, 8
• The natural history and response to treatment differ from cirrhotic causes 7