Extrahepatic causes of portal hypertension
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Extrahepatic Causes of Portal Hypertension
Portal hypertension is classified by the anatomical site of increased resistance: prehepatic (before the liver), intrahepatic (within the liver), and posthepatic (after the liver). "Extrahepatic" causes therefore encompass both the prehepatic and posthepatic groups.
Intrahepatic causes account for >95% of all portal hypertension cases (cirrhosis being dominant), but extrahepatic causes are clinically important and often affect younger patients with preserved liver function. - Harrison's Principles of Internal Medicine 22E, p. 1283
I. Prehepatic Causes
These obstruct the portal venous system before it enters the liver. Portal pressure is elevated, but liver function tests and hepatic venous pressure gradient (HVPG) are usually normal (the liver itself is unaffected).
1. Portal Vein Thrombosis (PVT) - Most Common Prehepatic Cause
The most common prehepatic cause, responsible for ~50% of portal hypertension cases in children. - Sabiston Textbook of Surgery
Causes / Risk factors (Virchow's triad applies):
| Category | Examples |
|---|---|
| Thrombophilia (hypercoagulable states) | Polycythemia vera, essential thrombocythemia, JAK2 mutation, protein C/S/antithrombin III deficiency, factor V Leiden, antiphospholipid syndrome, paroxysmal nocturnal hemoglobinuria |
| Local / endothelial injury | Pancreatitis, IBD, diverticulitis, abdominal trauma, post-splenectomy, umbilical vein sepsis (neonates) |
| Reduced portal flow / external compression | Hepatocellular carcinoma invasion, cirrhosis |
| Other | Oral contraceptive use, pregnancy |
Presentation:
- Acute PVT: abdominal pain, fever, ascites, intestinal ischemia (if SMV involved)
- Chronic PVT: often asymptomatic, or presents with variceal bleeding, splenomegaly, thrombocytopenia; leads to portal cavernoma (collateral vein formation replacing the thrombosed vein)
Diagnosis: Doppler ultrasonography is the first-line test.
Extrahepatic portal vein thrombosis is after cirrhosis the second most common cause of portal hypertension in children. - Grainger & Allison's Diagnostic Radiology
2. Splenic Vein Thrombosis
Causes segmental (left-sided) portal hypertension - only the splenic venous territory is hypertensive. The portal vein itself remains patent, so liver function is normal.
- Most common cause: Chronic pancreatitis (>50% of cases)
- Other causes: pancreatic carcinoma, pancreatic pseudocyst, trauma
- Presentation: Gastric varices (predominantly fundal/short gastric), splenomegaly; esophageal varices are less common
- Treatment: Splenectomy is curative in symptomatic patients - Frameworks for Internal Medicine
3. Extrinsic Compression / Invasion of the Portal Vein
- Malignant tumors (e.g., pancreatic carcinoma, cholangiocarcinoma, lymphoma with bulky nodes)
- Benign masses, retroperitoneal hematoma
- Portal stenting may be considered in selected cases
4. Splanchnic Arteriovenous Fistula
A rare cause that acts by increasing portal blood flow rather than increasing resistance.
- Causes: Abdominal trauma, spontaneous rupture of a splenic artery aneurysm (higher frequency in pregnancy), hereditary hemorrhagic telangiectasia (HHT/Osler-Weber-Rendu)
- Produces sudden, dramatic increase in portal pressure
- Auscultation may reveal an abdominal bruit - Frameworks for Internal Medicine
5. Massive Splenomegaly / Increased Splenic Blood Flow (Banti's Syndrome)
- Massive splenomegaly (e.g., from myelofibrosis, tropical splenomegaly/hyperreactive malarial splenomegaly, Gaucher disease, hairy cell leukemia) increases splenic venous outflow to the point of causing portal hypertension
- Harrison's lists this as a prehepatic cause (Table 355-3)
II. Posthepatic Causes
These obstruct venous drainage from the liver toward the heart. The HVPG is elevated, and the liver is secondarily affected (congestive hepatopathy). Importantly, the HVPG does reflect the gradient in these cases.
1. Budd-Chiari Syndrome (Hepatic Vein Outflow Obstruction)
Obstruction of hepatic vein outflow - the most important posthepatic cause.
Causes:
- Thrombophilia: myeloproliferative disorders (especially polycythemia vera - most common underlying cause), antiphospholipid syndrome, protein C/S deficiency
- Oral contraceptives
- Paroxysmal nocturnal hemoglobinuria
- Behcet's disease
- Pregnancy / postpartum
- Hepatic tumors invading hepatic veins
- Membranous obstruction of IVC (especially in Asia/Africa)
Presentation:
- Acute: Abdominal pain, ascites, hepatomegaly (classic triad)
- Chronic: Often asymptomatic; features of portal hypertension (varices, ascites, splenomegaly)
- Diagnosis: Doppler ultrasonography (first-line) - Frameworks for Internal Medicine
2. Inferior Vena Cava (IVC) Obstruction
- Membranous webs of the IVC (seen commonly in India, Japan, South Africa) - a distinct entity causing chronic Budd-Chiari-like syndrome
- Thrombosis or tumor invasion of the IVC
- Raises back-pressure into hepatic veins
3. Cardiac Causes (Congestive Hepatopathy)
Right-sided cardiac disease transmits venous back-pressure through the IVC into hepatic veins and sinusoids.
| Condition | Key Feature |
|---|---|
| Congestive cardiac failure (cor pulmonale, cardiomyopathy, valvular disease, ischemic disease) | Raised JVP, ascites; pulsatile liver in severe tricuspid regurgitation (Lancisi's sign) |
| Constrictive pericarditis | Kussmaul's sign, elevated JVP; ascites present in ~50%; must be distinguished from liver disease |
| Restrictive cardiomyopathy | Elevated filling pressures on both sides |
| Severe tricuspid regurgitation | Lancisi's sign (CV fusion wave in JVP), pulsatile liver palpable |
Ascites occurs in almost one-half of patients with constrictive pericarditis. Elevated JVP is the key clue that ascites is primarily cardiac rather than hepatic. - Frameworks for Internal Medicine
4. Hepatic Sinusoidal Obstruction Syndrome (SOS) / Veno-Occlusive Disease (VOD)
- Classified as postsinusoidal (intrahepatic posthepatic level) but often grouped with posthepatic causes
- Caused by cytotoxic drugs (especially cyclophosphamide, busulfan used in stem cell transplant conditioning), pyrrolizidine alkaloids (herbal teas), radiation
- Endothelial injury of small hepatic venules leads to sinusoidal outflow obstruction
- Presents with painful hepatomegaly, jaundice, ascites within days to weeks of conditioning
Summary Table
| Category | Cause | Mechanism |
|---|---|---|
| Prehepatic | Portal vein thrombosis | Intraluminal obstruction |
| Splenic vein thrombosis | Segmental portal HTN | |
| Extrinsic compression (tumor, nodes) | Extraluminal obstruction | |
| Splanchnic AV fistula | Increased inflow | |
| Massive splenomegaly (Banti's) | Increased inflow | |
| Posthepatic | Budd-Chiari syndrome | Hepatic vein obstruction |
| IVC obstruction / webs | Venous outflow block | |
| Right heart failure | Back-pressure | |
| Constrictive pericarditis | Back-pressure | |
| Restrictive cardiomyopathy | Back-pressure | |
| Tricuspid regurgitation | Back-pressure (pulsatile) | |
| Hepatic SOS/VOD | Postsinusoidal obstruction |
Key clinical distinctions:
- Prehepatic: Liver function normal, HVPG normal, good prognosis from bleeding
- Posthepatic: Elevated HVPG, congestive hepatopathy, look for cardiac signs / elevated JVP
- Splenic vein thrombosis is a unique subset - segmental hypertension with predominantly gastric varices; splenectomy is curative
Sources:
- Sleisenger and Fordtran's Gastrointestinal and Liver Disease, Box 92.1 / p. 1769-1770
- Harrison's Principles of Internal Medicine 22E, Table 355-3, p. 1282-1283
- Bailey and Love's Short Practice of Surgery 28th Ed., p. 1224-1225
- Fischer's Mastery of Surgery 8th Ed., Table 194.1
- Robbins, Cotran & Kumar Pathologic Basis of Disease, Table 18.2
- Frameworks for Internal Medicine, pp. 167-170 (Prehepatic/Posthepatic sections)
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