Azygos system
Receives esophageal veins and returns blood to superior vena cava.
GI
Portosystemic Anastomoses
Portal hypertension reroutes blood through named venous junctions; the surface sign reveals the escape path and its systemic destination.
- Map the major portal-systemic venous connections
- Distinguish anorectal varices from hemorrhoids
- Explain how TIPS lowers portal pressure and raises encephalopathy risk
Anatomic relationships
Use the landmarks before naming the lesion
The figure shows the location and nearby structures that distinguish the diagnosis.
Quick check
In cirrhosis, dilated veins in the lower esophageal submucosa rupture and cause massive hematemesis.
Which portal tributary meets which systemic drainage at this site?
Reason it through
- Which portal vein reaches the lower esophagus?The left gastric vein supplies the portal side of the collateral.
- Which systemic network receives the esophageal veins?They drain through the azygos system toward the superior vena cava.
Trace portal blood around the liver
Start with the clinical site, then follow collateral blood until it reaches a caval system.
Esophageal collaterals enter azygos and hemiazygos pathways before reaching the superior vena cava.
Paraumbilical flow spreads through epigastric and thoracoepigastric veins toward both superior and inferior vena caval systems.
Anorectal collateral blood reaches internal iliac circulation through middle rectal veins and internal pudendal circulation through inferior rectal veins.
Open each systemic destination.
Epigastric veins
Carry paraumbilical collateral flow across anterior abdominal wall.
Internal iliac veins
Receive middle rectal systemic drainage.
Internal pudendal veins
Receive inferior rectal drainage below the pectinate line.
Three classic collateral sites
The visible or bleeding site identifies the portal tributary and its systemic exit.
At the lower esophagus, the left gastric vein joins esophageal veins that drain into the azygos system; dilation creates esophageal varices.
At the umbilicus, paraumbilical veins connect with superficial and deep epigastric veins of the anterior abdominal wall; dilation creates caput medusae.
At the rectum and anal canal, superior rectal portal drainage communicates with middle and inferior rectal systemic drainage; dilation creates anorectal varices.
Switch among the collateral sites.
Left gastric to esophageal veins to azygos; risk of life-threatening upper GI bleeding.
Paraumbilical to epigastric veins; radiating abdominal-wall collaterals.
Superior rectal to middle and inferior rectal veins; anorectal varices.
Name the paired veins, not just the esophageal, umbilical, or anorectal site.
How portal hypertension opens collaterals
Rising portal resistance enlarges preexisting venous exits into fragile collateral channels.
Cirrhosis and other causes of portal resistance raise pressure in tributaries before blood can traverse hepatic sinusoids.
Blood shifts into preexisting low-capacity communications, which enlarge as flow seeks lower-resistance systemic veins.
The detour partly relieves portal pressure but produces fragile varices, visible abdominal-wall veins, splenomegaly, and loss of hepatic first-pass clearance.
Reveal the pressure-to-varix sequence.
- Resistance rises within or beyond liver
Portal inflow meets an obstructed pathway.
- Portal venous pressure increases
Upstream tributaries become congested.
- Embryologic venous communications reopen
Blood follows lower-resistance systemic routes.
- Collateral veins dilate
Thin-walled channels become tortuous varices.
- Complications appear
Bleeding, ascites, splenomegaly, and shunting-related toxin exposure follow.
Anorectal varices are not hemorrhoids
Shared location does not make anorectal varices and hemorrhoids the same lesion.
Portal hypertension dilates portosystemic collateral veins into anorectal varices that may extend above and below the pectinate line.
Hemorrhoids arise from symptomatic enlargement or displacement of normal anal vascular cushions, with local contributors such as straining, constipation, pregnancy, and support-tissue changes.
A painful anal mass is not automatically a portal collateral, and external hemorrhoids below the pectinate line retain somatic innervation.
Which lesion directly reflects portal hypertension?
Portal pressure produces anorectal varices; ordinary hemorrhoids follow a different mechanism.
Portal flow direction reverses in collaterals
Normal portal flow heads toward liver, whereas advanced collateral flow diverts blood away from it.
Normally, portal venous blood enters liver, crosses sinusoids, and leaves through hepatic veins for the inferior vena cava.
Portosystemic collaterals and TIPS redirect part of that inflow into systemic venous channels before normal sinusoidal processing.
Classify each pathway by how much liver processing it preserves.
More hepatic processing
More bypass
More bypass
More bypass
Bypassing liver lowers portal pressure and reduces ammonia clearance through the same shortcut.
TIPS creates a controlled shortcut
TIPS deliberately creates a low-resistance channel around sinusoidal resistance.
A transjugular intrahepatic portosystemic shunt links a portal venous branch with hepatic venous outflow inside the liver.
By lowering the portal-systemic pressure gradient, the channel can control variceal bleeding or refractory ascites.
The same bypass sends more gut-derived ammonia and other substances past hepatocyte metabolism, increasing the risk of hepatic encephalopathy.
Open the benefit and tradeoff.
Portal blood enters hepatic venous outflow without traversing high-resistance sinusoids.Lower variceal pressure reduces recurrent hemorrhage risk in selected patients.Reduced portal hydrostatic pressure can improve refractory ascites.Less hepatic detoxification increases systemic exposure to ammonia and other neurotoxins.Increased venous return can worsen heart failure or pulmonary hypertension in susceptible patients.
Stage 1 of 3: Overview
Overview
Portosystemic Anastomoses
Rising portal resistance enlarges preexisting venous exits into fragile collateral channels.
Localization check
Which landmark matters most?
Choose the location that rules the other answer choices in or out.
Which portal tributary meets which systemic drainage at this site?
- Key finding. lower esophageal submucosa
- Answer. Left gastric vein and esophageal veins draining to the azygos system
- Why. Portal left-gastric tributaries communicate with systemic esophageal veins that drain toward azygos circulation.
- Board rule. Lower-esophageal varices connect the left gastric vein to esophageal veins of the azygos system.
Follow each portal escape route
Five problems connect surface findings, TIPS physiology, thoracic drainage, and collateral formation.
Cross out wrong locations and highlight the decisive landmark. Each case connects anatomy to its clinical consequence.
Portal hypertension produces radiating, tortuous veins around the umbilicus.
Which portal veins feed this collateral pattern?
Reason it through
- What visible pattern localizes the collateral route?Radiating veins around the umbilicus identify caput medusae.
- Which portal tributaries run through that region?Paraumbilical veins provide the portal side of the connection.
- Which systemic veins receive the redirected flow?Superficial and deep epigastric veins carry it into systemic circulation.
around the umbilicusWhich portal tributaries run through that region?
- What visible pattern localizes the collateral route?Radiating veins around the umbilicus identify caput medusae.
- Which portal tributaries run through that region?Paraumbilical veins provide the portal side of the connection.
- Which systemic veins receive the redirected flow?Superficial and deep epigastric veins carry it into systemic circulation.
After TIPS placement, a patient develops confusion and asterixis.
What change in portal handling caused this complication?
Reason it through
- What normal hepatic route did TIPS bypass?The shunt directs portal blood around sinusoidal and hepatocyte processing.
- Which gut-derived substance is then cleared less effectively?Ammonia reaches systemic circulation more readily.
- How does that change explain the neurologic signs?Reduced hepatic ammonia clearance can precipitate hepatic encephalopathy with confusion and asterixis.
confusion and asterixisWhich gut-derived substance is then cleared less effectively?
- What normal hepatic route did TIPS bypass?The shunt directs portal blood around sinusoidal and hepatocyte processing.
- Which gut-derived substance is then cleared less effectively?Ammonia reaches systemic circulation more readily.
- How does that change explain the neurologic signs?Reduced hepatic ammonia clearance can precipitate hepatic encephalopathy with confusion and asterixis.
Endoscopy in cirrhosis shows dilated veins in the lower esophagus.
Which systemic route ultimately receives this collateral blood?
Reason it through
- Which portal tributary supplies the varices?The left gastric vein supplies the portal side.
- Where do the communicating esophageal veins drain?They empty into azygos circulation.
- Which vena cava receives the azygos outflow?The azygos system returns this blood to the superior vena cava.
lower esophagusWhere do the communicating esophageal veins drain?
- Which portal tributary supplies the varices?The left gastric vein supplies the portal side.
- Where do the communicating esophageal veins drain?They empty into azygos circulation.
- Which vena cava receives the azygos outflow?The azygos system returns this blood to the superior vena cava.
A venogram shows esophageal veins entering a thoracic venous network that returns blood to the superior vena cava.
Which venous network is shown?
Reason it through
- Which tributaries enter the labeled thoracic network?Esophageal veins enter it.
- What is the network's terminal systemic destination?Its blood returns to the superior vena cava.
- Which option matches both the tributary and destination?The azygos system receives esophageal veins and drains to the superior vena cava.
returns blood to the superior vena cavaWhat is the network's terminal systemic destination?
- Which tributaries enter the labeled thoracic network?Esophageal veins enter it.
- What is the network's terminal systemic destination?Its blood returns to the superior vena cava.
- Which option matches both the tributary and destination?The azygos system receives esophageal veins and drains to the superior vena cava.
In cirrhosis, resistance to portal flow raises portal venous pressure.
Which structural response begins collateral decompression?
Reason it through
- Where does resistance trap pressure?Pressure rises upstream in portal tributaries.
- Which latent channels can accept the diverted blood?Preexisting embryologic venous communications can reopen.
- Why does flow enter those communications?They offer lower-resistance routes into systemic veins.
portal venous pressureWhich latent channels can accept the diverted blood?
- Where does resistance trap pressure?Pressure rises upstream in portal tributaries.
- Which latent channels can accept the diverted blood?Preexisting embryologic venous communications can reopen.
- Why does flow enter those communications?They offer lower-resistance routes into systemic veins.
Rapid review
Three questions to check
Which portal tributary meets which systemic drainage at this site?
Left gastric vein and esophageal veins draining to the azygos system. Portal left-gastric tributaries communicate with systemic esophageal veins that drain toward azygos circulation.
What visible pattern localizes the collateral route?
Radiating veins around the umbilicus identify caput medusae.
Which portal tributaries run through that region?
Paraumbilical veins provide the portal side of the connection.
Medically reviewed
Fatima Ali, DO
PGY-1 Resident Physician in Psychiatry
University Hospitals, Columbia
DO from Kansas City University
Resident physician and founding medical reviewer at Bone Wizardry, focused on clinical accuracy, clear diagnostic reasoning, and practical board-oriented teaching across the curriculum.
Languages: English, Urdu
Primary reviewerFull physician profile
Medically reviewed
Sources
- Portal Hypertension2026
- Transjugular Intrahepatic Portosystemic Shunt2026
- Anatomy, Abdomen and Pelvis: Anal Canal2026
- Physiology, Liver2026
Bone Wizardry is a study resource for medical students. It is not medical advice.