Is an IMV Venous Varix Considered a Hepatic Venous Collateral?
No, an inferior mesenteric vein (IMV) varix is not a hepatic venous collateral—it is a portal venous collateral that develops in response to portal hypertension, not hepatic venous outflow obstruction.
Anatomical and Hemodynamic Distinction
The IMV drains into the portal venous system (specifically into the splenic vein or superior mesenteric vein), making it part of the portal circulation rather than the hepatic venous outflow tract 1. When portal hypertension develops:
- IMV varices represent portal-systemic collaterals that shunt blood away from the liver through alternative pathways, typically connecting to rectal veins and hemorrhoidal plexuses 2
- Hepatic venous collaterals, by contrast, form specifically in response to hepatic venous outflow obstruction (as seen in Budd-Chiari syndrome) and include intrahepatic or subcapsular collaterals connecting hepatic veins to diaphragmatic or intercostal veins 1
Hepatic Venous Collaterals: Defining Characteristics
True hepatic venous collaterals are diagnostic features of Budd-Chiari syndrome and have specific imaging characteristics 1, 3:
- Large intrahepatic or subcapsular collaterals with continuous flow connecting the hepatic veins to the diaphragmatic or intercostal veins are found in more than 80% of Budd-Chiari cases 1, 3
- These collaterals represent alternative drainage pathways when the main hepatic veins or IVC are obstructed 1
- A "coarse network of collateral veins which arch outward from the catheter tip and then come together again near the site of entry of the hepatic vein into the IVC" is considered specific for hepatic venous obstruction on venography 1
Clinical Implications of IMV Flow Patterns
The IMV functions as a portal collateral with distinct clinical associations 2:
- Hepatofugal (reversed) IMV flow is associated with more severe portal hypertension, increased ascites, higher rates of liver decompensation, and increased rectal varices 2
- Hepatopetal (normal direction) IMV flow is associated with higher rates of gastroesophageal varices (80.4% vs 51.5% with hepatofugal flow) 2
- IMV collaterals do not affect survival when stratified by liver function, unlike the prognostic significance of hepatic venous collaterals in Budd-Chiari syndrome 2
Critical Diagnostic Pitfall to Avoid
Do not confuse portal venous collaterals (including IMV varices) with hepatic venous collaterals, as this distinction is essential for accurate diagnosis:
- Portal collaterals indicate portal hypertension from cirrhosis, portal vein thrombosis, or other causes of increased portal pressure 2
- Hepatic venous collaterals specifically indicate hepatic venous outflow obstruction and are a distinctive feature separating Budd-Chiari syndrome from cirrhosis 1, 3
- The presence of intrahepatic or subcapsular hepatic venous collaterals on Doppler ultrasound is found in over 80% of Budd-Chiari cases and helps differentiate it from other causes of liver disease 1, 3