What is portal hypertension?

What is Portal Hypertension?

Portal hypertension is a pathological increase in portal venous pressure, defined as a hepatic venous pressure gradient (HVPG) above 5 mmHg, with clinically significant portal hypertension (CSPH) occurring at HVPG ≥10 mmHg. 1

Pathophysiology

Portal hypertension develops through two primary mechanisms that follow the hydraulic equivalent of Ohm's law where "Pressure = Resistance × Flow": 1, 2

• Increased intrahepatic resistance is the primary driver, comprising both structural (70%) and functional (30%) components 1

  • The structural component results from fibrous tissue deposition, vascular distortion from regenerative nodules, and microthrombi formation 1
  • The functional component stems from endothelial dysfunction with reduced nitric oxide bioavailability, leading to contraction of activated hepatic stellate cells 1

• Increased portal blood flow occurs secondary to splanchnic vasodilation, which further aggravates the elevated portal pressure 3

Clinical Significance and Pressure Thresholds

The severity of portal hypertension directly correlates with clinical outcomes: 1

• Normal HVPG: 1-5 mmHg
• Portal hypertension: HVPG >5 mmHg
• Clinically significant portal hypertension (CSPH): HVPG ≥10 mmHg—this threshold marks when patients face higher risk of clinical decompensation 1
• High mortality risk: HVPG ≥16 mmHg—strongly associated with death 1

HVPG ≥10 mmHg is the critical threshold because it predicts development of portal hypertension-related complications including varices, ascites, and hepatic encephalopathy. 1

Major Clinical Manifestations

Portal hypertension produces several life-threatening complications: 2

• Gastroesophageal varices: Dilated submucosal veins in the lower esophagus and stomach that can rupture, causing life-threatening hemorrhage—this is the most frequent and serious complication 2
• Ascites: Abnormal fluid accumulation in the peritoneal cavity, representing the most common complication overall; survival decreases from 80% at 5 years in compensated cirrhosis to 50% when ascites develops 1
• Splenomegaly with hypersplenism: Enlarged spleen leading to thrombocytopenia and leukopenia 2
• Hepatic encephalopathy: Neuropsychiatric dysfunction from portosystemic shunting 4

Etiology

Cirrhosis from any chronic liver disease is the predominant cause of portal hypertension, accounting for the majority of cases. 5 The increased intrahepatic resistance can occur at presinusoidal, sinusoidal, or postsinusoidal levels depending on the specific liver disease 4. Primary biliary cirrhosis can develop portal hypertension early, even before established cirrhosis 5.

Diagnostic Approach

HVPG measurement is the gold standard for diagnosing and quantifying portal hypertension. 1, 5 However, since HVPG is invasive with technical limitations, noninvasive alternatives are increasingly used: 4

• Transient elastography (TE): Sensitivity 90-96% and specificity 48-50% at 15 kPa cutoff; CSPH is highly unlikely at liver stiffness measurement (LSM) ≤15 kPa and likely present at LSM ≥25 kPa 4, 1
• APRI score: 56% sensitivity and 68% specificity 1
• Doppler ultrasound: First-line investigation for extrahepatic portal vein obstruction, with CT for confirmation 1, 2

A common pitfall is relying solely on noninvasive tests when precise pressure measurement is needed for therapeutic decisions, as substantial heterogeneity exists in cutoff values and accuracy varies considerably. 4