CorpusHuman Anatomy
CardiovascularVessel

Portosystemic (portocaval) anastomoses

Anastomoses portocavales

Also known as: portosystemic anastomoses, portosystemic collaterals, varices

Portosystemic anastomoses are sites where tributaries of the hepatic portal system connect with systemic veins. Normally they carry very little blood. In portal hypertension they dilate into varices that carry blood around the liver.

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Overview

Portal blood has no valves to stop it flowing backward. When resistance to flow through the liver rises, as in cirrhosis, portal blood finds its way to systemic veins through small pre-existing connections. These enlarge into varices. The varices lower portal pressure somewhat, but they can bleed. They also carry gut-derived toxins such as ammonia around the liver, which causes hepatic encephalopathy.

Parts & subdivisions

  1. Oesophageal
    The left gastric vein (portal) connects with the oesophageal veins, which drain to the azygos and hemiazygos veins (systemic). Dilatation here produces oesophageal varices, the most dangerous site because of the risk of massive haematemesis.
  2. Anorectal
    The superior rectal vein (portal, via the IMV) connects with the middle and inferior rectal veins (systemic, via the internal iliac and internal pudendal veins). Dilatation produces anorectal varices. These are different from haemorrhoids, which are cushions of vascular tissue.
  3. Paraumbilical
    The paraumbilical veins, which run along the ligamentum teres to the portal vein, connect with the superficial epigastric and thoracoepigastric veins of the abdominal wall (systemic). Dilatation produces caput medusae, with blood flowing away from the umbilicus.
  4. Retroperitoneal
    Colic, splenic and pancreatic veins (portal) connect with renal, lumbar and phrenic veins (systemic) through the veins of Retzius. This happens where the bowel lies directly against the posterior abdominal wall.
  5. Bare area of the liver
    Small portal and hepatic veins in the liver connect with the phrenic and intercostal veins across the bare area of the liver.

Function

  • Normally insignificant. In portal hypertension they decompress the portal system by diverting blood into the systemic veins.

Clinical significance

Variceal haemorrhage

Bleeding from oesophageal or gastric varices is a medical emergency in cirrhosis. Management includes resuscitation, terlipressin and antibiotics, followed by endoscopic band ligation. TIPS is used if bleeding continues or recurs. Patients who have bled, or who have high-risk varices, are given non-selective β-blockers and banding to prevent further bleeds.

Caput medusae versus IVC obstruction

In caput medusae from portal hypertension, blood in the abdominal wall veins flows away from the umbilicus. In IVC obstruction, collateral veins in the abdominal wall carry blood upward from below the umbilicus.

Mnemonics

Sites of portosystemic varices

"Gut, Butt, Caput": oesophageal varices, anorectal varices and caput medusae.

Test yourself

Oesophageal varices in portal hypertension develop at an anastomosis between which veins?
  1. Left gastric vein and oesophageal tributaries of the azygos vein
  2. Superior rectal vein and inferior rectal veins
  3. Paraumbilical veins and superficial epigastric veins
  4. Splenic vein and left renal vein

Answer: Left gastric vein and oesophageal tributaries of the azygos vein

The left gastric (coronary) vein belongs to the portal system and the oesophageal veins drain into the azygos (systemic) system. When portal pressure rises they dilate into oesophageal varices, which can bleed catastrophically. The other options describe the anorectal, paraumbilical and retroperitoneal anastomoses.

More cardiovascular system questions

Compiled from standard anatomy and physiology references — see the Cardiovascular System sources. For education only; not medical advice.