What are the primary causes of rectal varices?

Primary Causes of Rectal Varices

Portal hypertension is the primary cause of rectal varices, which develop as portosystemic collaterals when portal pressure increases above a threshold. 1

Pathophysiology of Rectal Varices

Rectal varices form as a result of portal hypertension through the following mechanisms:

• Portal pressure increases due to increased resistance to flow, primarily from architectural distortion of the liver caused by fibrous tissue and regenerative nodules in cirrhosis 1
• Active intrahepatic vasoconstriction accounts for 20-30% of the increased intrahepatic resistance, largely due to decreased endogenous nitric oxide production 1
• When portal pressure rises above the threshold (hepatic venous pressure gradient >10-12 mmHg), portosystemic collaterals develop at sites of communication between portal and systemic circulation 1
• Rectal varices specifically form through portocaval anastomosis between the superior rectal vein (portal system) and the middle/inferior rectal veins (systemic circulation) 2

Specific Causes of Portal Hypertension Leading to Rectal Varices

Hepatic Causes

• Cirrhosis (most common cause) 1
  • Alcoholic cirrhosis 1
  • Viral hepatitis-related cirrhosis 1
  • Primary biliary cirrhosis 1
• Advanced fibrosis without cirrhosis
  • Hepatitis C with bridging fibrosis (16% have varices even before cirrhosis) 1

Pre-hepatic Causes

• Extrahepatic portal vein obstruction (prevalence of rectal varices reported as high as 94% in these patients) 3
• Portal vein thrombosis 3
• Splenic vein thrombosis 3

Post-hepatic Causes

• Budd-Chiari syndrome 3
• Heart failure (can contribute to portal hypertension) 2

Risk Factors for Bleeding from Rectal Varices

• Severity of liver disease (Child-Pugh class B/C) 1
• Size of varices (larger varices have higher bleeding risk) 1, 3
• Higher portal pressure gradient (HVPG >20 mmHg) 1
• Presence of red spots on varices (endoscopic finding) 1
• Variceal wall tension (related to radius of the varix) 1

Clinical Significance

• Bleeding from rectal varices, though rare, can be massive and life-threatening 3, 4
• Mortality is significantly higher in patients with bleeding rectal varices compared to other sources of lower gastrointestinal bleeding (80% vs 13% within 2 months in one study) 1
• Rectal variceal hemorrhage often occurs in patients with liver cirrhosis at the final stage during progression of portal hypertension 1

Diagnostic Considerations

• Diagnosis is typically based on lower endoscopy (colonoscopy or sigmoidoscopy) 3
• Endoscopic ultrasonography is superior to standard endoscopy in diagnosing rectal varices 3
• Color Doppler ultrasonography allows calculation of blood flow velocity in varices and can help predict bleeding risk 3

Important Anatomical Variations

• Variant anatomy of the superior rectal vein can exist, such as direct drainage into the left portal vein without connectivity between the inferior mesenteric vein and rectal varices 2
• These anatomical variations can impact treatment approaches and should be identified before interventional procedures 2

Prompt differentiation between hemorrhoids and rectal varices is crucial for proper management, as the treatments and prognosis differ significantly 4.