What is Extrahepatic Portal Vein Obstruction (EHPVO)?

What is Extrahepatic Portal Vein Obstruction (EHPVO)?

Extrahepatic portal vein obstruction (EHPVO) is a primary vascular condition characterized by chronic blockage and cavernous transformation of the portal vein, with or without involvement of intrahepatic branches, splenic vein, or superior mesenteric vein, resulting in portal hypertension while preserving liver function and morphology. 1, 2

Pathophysiology

• EHPVO develops when acute portal vein thrombosis fails to recanalize, leading to complete obliteration of the portal vein lumen and formation of porto-portal collaterals (cavernoma) that develop fully within a couple of months after the acute thrombotic event. 3

• The condition represents a pre-hepatic type of portal hypertension where the liver parenchyma remains essentially normal with preserved synthetic function, fundamentally distinguishing it from cirrhotic portal hypertension. 1, 4, 2

• Multiple serpiginous vascular channels form in the porta hepatis to bypass the obstructed portal vein, creating the characteristic "cavernomatous transformation." 1, 2

Clinical Presentation

Primary Manifestations

• Variceal bleeding is the most common presentation, particularly in children where EHPVO is the predominant cause of pediatric portal hypertension in developing countries. 2, 5

• Hypersplenism with splenomegaly and thrombocytopenia occurs frequently due to portal hypertension. 1, 5

• Patients may present with abdominal pain, particularly post-prandial pain or features suggesting incomplete bowel obstruction related to ischemic stenosis. 1, 6

Secondary Complications

• Portal biliopathy (portal cavernoma cholangiopathy) develops from parabiliary venous collaterals causing bile duct abnormalities, though symptomatic cases requiring intervention are uncommon. 1, 2, 7

• Recurrent thrombosis in the splanchnic area, though often asymptomatic and underestimated. 1

• Growth failure is a specific consequence in children due to growth hormone resistance from diminished portal blood flow and decreased insulin-like growth factor-1 production. 1, 7

• Ascites, bacterial infections, and overt encephalopathy are uncommon except following gastrointestinal bleeding, though subclinical encephalopathy may be more common than previously recognized. 1

Diagnostic Approach

Imaging Modalities

• Doppler ultrasound is the first-line investigation with high diagnostic accuracy for EHPVO. 1, 5

• CT or MR imaging with vascular contrast agents is essential for diagnostic confirmation and extension assessment. 1, 3

Essential Diagnostic Features

The diagnosis requires identification of two key imaging findings:

1. Absence of visible lumen corresponding to the portal vein 1, 3

2. Presence of numerous serpiginous vascular channels in the porta hepatis 1, 3

Additional Imaging Clues

• Dysmorphic liver with enlarged segments 1 and 4 but smooth surface 1

• Mosaic pattern of parenchymal enhancement in arterial phase with homogeneous enhancement later 1

• Increased peripheral liver enhancement in arterial phase 1

• Dilated hepatic artery 1

• Mild irregular dilatation of bile ducts 1

Critical Caveat

• Immediate CT imaging with IV contrast is essential if EHPVO is suspected with acute abdominal symptoms, rather than relying on plain radiographs, as CT can detect bowel wall enhancement abnormalities, mesenteric edema, and signs of ischemia not visible on X-ray. 6

When to Consider EHPVO

The diagnosis should be considered in:

• Any patient with features of portal hypertension or hypersplenism 1

• Patients with conditions associated with thrombotic risk: myeloproliferative neoplasms, antiphospholipid syndrome, inherited thrombophilic factors, pancreatitis, diverticulitis, inflammatory bowel disease 1

• Patients presenting with abdominal pain or biliary disease 1

• Rarely, presentations resembling decompensated cirrhosis (encephalopathy, ascites, bacterial infection) 1

Excluding Underlying Liver Disease

Liver biopsy is indicated when liver tests are persistently abnormal or the liver appears dysmorphic in a pattern not typical for extrahepatic venous obstruction. 1

• In pure portal vein obstruction, liver biopsy shows an essentially normal liver. 1

• Non-invasive elastometry is useful for recognizing underlying liver disease and distinguishing EHPVO from cirrhosis or obliterative portal venopathy. 1

• Rule out cirrhosis whenever liver tests are abnormal, a cause for chronic liver disease is present, the liver is dysmorphic, or elastometry results are abnormal. 1

Etiology

• Idiopathic in most pediatric cases, though neonatal umbilical vein catheterization is a recognized risk factor. 5, 8

• In adults, underlying prothrombotic disorders and local factors are common and constitute major determinants of outcome requiring specific therapy. 1

• Studies in children have not consistently documented hereditary or acquired coagulation disorders as causative factors. 7

Key Distinguishing Feature from Cirrhosis

EHPVO produces portal hypertension through mechanical obstruction and cavernomatous transformation but does not trigger the systemic circulatory dysfunction and renal vasoconstriction that define hepatorenal syndrome, as the liver synthetic function remains preserved and characteristic hemodynamic derangements of cirrhosis are absent. 4