Portal Vein & Portosystemic Anastomoses

The portal venous system carries nutrient-rich, deoxygenated blood from the abdominal gut (lower oesophagus to upper anal canal), spleen, pancreas, and gallbladder to the liver for first-pass processing. When this circuit obstructs, blood reroutes through portosystemic anastomoses — the anatomical basis of oesophageal varices, caput medusae, and haemorrhoids. This is among the most repeatedly tested anatomy-hepatology overlap areas in NEET PG.

Formation, Course & Tributaries of the Portal Vein

The hepatic portal vein is about 8 cm long and is formed by the union of the superior mesenteric vein (SMV) and the splenic vein, behind the neck of the pancreas at the level of L2 (transpyloric plane).

Formation flow: Splenic vein + Superior mesenteric vein → (behind neck of pancreas) → Portal vein → ascends in the right free margin of the lesser omentum (hepatoduodenal ligament) → divides at the porta hepatis into right and left branches.

High-yield: The portal vein is formed behind the neck of the pancreas; it is the most posterior structure in the free margin of the lesser omentum (anterior relations: bile duct to the right, hepatic artery to the left — mnemonic DAVE: Duct Anterior right, Vein posterior, Artery anterior left).

The inferior mesenteric vein (IMV) usually drains into the splenic vein (most common), though it may join the SMV or the splenic–SMV junction.

Tributaries of the Portal Vein

Tributary	Drains	Notes
Superior mesenteric vein	Small intestine, caecum, ascending & transverse colon, head of pancreas	One of two roots
Splenic vein	Spleen, fundus of stomach, body of pancreas	One of two roots; receives IMV
Left gastric (coronary) vein	Lesser curve of stomach, lower oesophagus	Site of oesophageal varices
Right gastric vein	Lesser curve (pylorus)	Receives prepyloric vein of Mayo
Superior pancreaticoduodenal vein	Pancreas, duodenum	—
Cystic vein	Gallbladder	May drain into right branch
Para-umbilical veins	Anterior abdominal wall	Run in falciform ligament

High-yield: The portal vein has no valves — this valvelessness allows reverse (hepatofugal) flow during portal hypertension, which is why anastomoses engorge and varices form.

High-yield: Unique among large veins, the portal vein begins and ends in capillaries — it starts in gut/spleen capillaries and ends in the hepatic sinusoids (a portal system = capillaries at both ends).

Segmental & Intrahepatic Distribution

At the porta hepatis the portal vein divides into:

• Right branch — shorter, wider; receives the cystic vein; supplies segments V, VI, VII, VIII.
• Left branch — longer; supplies segments II, III, IV; connects to the ligamentum teres (obliterated left umbilical vein) and ligamentum venosum (obliterated ductus venosus).

The caudate lobe (segment I) drains directly into the IVC by its own small veins — clinically relevant in Budd–Chiari syndrome, where the caudate hypertrophies because it bypasses the obstructed major hepatic veins.

Portal Hypertension — Pathophysiology

Normal portal pressure is 5–10 mmHg; the hepatic venous pressure gradient (HVPG) = wedged hepatic venous pressure − free hepatic venous pressure, normally 3–5 mmHg.

HVPG value	Significance
> 5 mmHg	Portal hypertension (definition)
≥ 10 mmHg	"Clinically significant" — varices begin to form
≥ 12 mmHg	Threshold for variceal bleeding & ascites
> 16–20 mmHg	Predicts poor outcome / rebleeding

Causes by site:

Site	Examples
Pre-hepatic	Portal vein thrombosis, splenic vein thrombosis, congenital atresia
Intrahepatic — presinusoidal	Schistosomiasis (commonest worldwide cause of presinusoidal PHT), congenital hepatic fibrosis, sarcoidosis
Intrahepatic — sinusoidal	Cirrhosis (commonest overall), alcoholic hepatitis
Post-sinusoidal	Veno-occlusive disease (pyrrolizidine alkaloids)
Post-hepatic	Budd–Chiari (hepatic vein/IVC obstruction), constrictive pericarditis, right heart failure

High-yield: Cirrhosis is the commonest cause of portal hypertension overall; non-cirrhotic portal fibrosis (NCPF) and extrahepatic portal vein obstruction (EHPVO) are important Indian causes; schistosomiasis is the commonest cause worldwide of presinusoidal portal hypertension.

The Four Sites of Portosystemic Anastomosis

When portal pressure rises, blood seeks alternative routes to the systemic (caval) circulation wherever portal and systemic tributaries meet. There are four classic sites plus retroperitoneal/patent ductus venosus contributions.

Mnemonic — "Caput, Cruveilhier, Varices, Piles": the four sites are lower oesophagus, peri-umbilical, rectum/anal canal, and retroperitoneum (bare area of liver).

Site	Portal tributary	Systemic tributary	Clinical result
Lower oesophagus (T8 level)	Left gastric (oesophageal branches)	Azygos / hemiazygos → SVC	Oesophageal varices (bleed → haematemesis)
Peri-umbilical	Para-umbilical veins (in falciform lig.)	Superficial/inferior epigastric, thoraco-epigastric	Caput medusae
Anal canal (above pectinate line)	Superior rectal vein (from IMV)	Middle & inferior rectal veins → internal iliac	Internal haemorrhoids (portal/varices type)
Retroperitoneal	Colic/splenic/pancreatic tributaries (veins of Retzius)	Renal, lumbar, phrenic veins	Asymptomatic; may cause retroperitoneal bleed
Bare area of liver	Portal radicles	Veins of Sappey → diaphragmatic/phrenic	Minor
Patent ductus venosus / Cruveilhier–Baumgarten	Left portal vein	Recanalised umbilical vein	Cruveilhier–Baumgarten murmur

1. Lower Oesophageal Anastomosis → Oesophageal Varices

At the gastro-oesophageal junction, the oesophageal branches of the left gastric (coronary) vein (portal) anastomose with oesophageal tributaries of the azygos system (systemic). In portal hypertension these submucosal veins dilate into oesophageal varices that lie just beneath the mucosa and rupture → massive painless haematemesis — the most lethal complication.

High-yield: Oesophageal varices are the most clinically important and most dangerous portosystemic communication. First-line drug for control of acute variceal bleed is octreotide / terlipressin (splanchnic vasoconstrictors); definitive control is endoscopic band ligation; non-selective beta-blockers (propranolol, nadolol, carvedilol) for primary & secondary prophylaxis.

2. Peri-umbilical Anastomosis → Caput Medusae

The para-umbilical veins run in the falciform ligament alongside the ligamentum teres and connect the left branch of the portal vein to the superficial epigastric / thoraco-epigastric veins of the anterior abdominal wall. Engorgement produces dilated, radiating subcutaneous veins around the umbilicus — caput medusae ("head of Medusa").

High-yield: Flow in caput medusae radiates away from the umbilicus (above umbilicus → upward, below → downward). This contrasts with IVC obstruction, where dilated veins on the abdominal wall carry blood upward from groin to chest to bypass the block — direction of flow distinguishes the two in MCQs.

3. Anal Canal Anastomosis → Haemorrhoids

The superior rectal vein (continuation of the IMV → portal) anastomoses with the middle and inferior rectal veins (→ internal iliac → systemic) in the wall of the anal canal above the pectinate line.

High-yield: Portal hypertension causes internal haemorrhoids here, but exam favourites note that classic primary haemorrhoidal disease is not mainly due to portal hypertension; anorectal varices are a separate entity. Internal haemorrhoids lie at the classic 3, 7, 11 o'clock positions (lithotomy).

4. Retroperitoneal / Bare-Area Anastomoses

The veins of Retzius connect retroperitoneal portions of gut (colon, duodenum, pancreas) to the renal, lumbar and phrenic systemic veins; the veins of Sappey drain the bare area of the liver to phrenic/diaphragmatic veins. These rarely cause visible signs but are a route for spontaneous portosystemic shunts seen on CT.

TIPS — Transjugular Intrahepatic Portosystemic Shunt

A TIPS is an artificial low-resistance channel created within the liver to decompress the portal system. Understanding the anatomy is a recurrent NEET PG image/MCQ.

TIPS pathway: Right internal jugular vein → SVC → right atrium → IVC → hepatic vein (usually right) → through liver parenchyma → branch of the portal vein (usually right) → stent deployed connecting hepatic vein to portal vein.

High-yield: TIPS connects the hepatic vein to the portal vein (a side-to-side intrahepatic shunt). Its major complication is new-onset or worsening hepatic encephalopathy (~30%) because nitrogenous blood bypasses hepatic detoxification; it also relieves refractory ascites and variceal bleeding.

Clinical Features of Portal Hypertension

The classic triad/tetrad: splenomegaly, ascites, varices (porto-systemic collaterals), and hepatic encephalopathy.

• Splenomegaly — congestive; may cause hypersplenism (pancytopenia).
• Ascites — multifactorial: portal hypertension + hypoalbuminaemia + RAAS activation; SAAG ≥ 1.1 g/dL indicates portal hypertensive ascites.
• Variceal bleeding — gastro-oesophageal, the leading cause of mortality.
• Caput medusae and venous hum.
• Hepatic encephalopathy — from shunting of ammonia past the liver.

High-yield: Cruveilhier–Baumgarten syndrome = recanalised umbilical/para-umbilical vein producing a venous hum over the epigastrium/umbilicus that diminishes on pressure above the umbilicus; with a palpable thrill it is the Cruveilhier–Baumgarten murmur.

Diagnosis & Investigation of Choice

Stepwise approach: Clinical suspicion → Doppler ultrasound (first-line, screening) → CT/MR portovenography (collaterals, anatomy) → Upper GI endoscopy (gold standard for varices) → HVPG measurement (gold standard for portal pressure).

Investigation	Role
Doppler USG	Best initial — portal vein diameter (>13 mm suggests PHT), flow direction (hepatofugal), patency, thrombosis
Upper GI endoscopy	Investigation of choice for detecting & grading oesophageal varices
HVPG	Gold standard to quantify portal pressure (≥10 mmHg significant)
CT/MR angiography	Maps collaterals, spleen, varices, vascular anatomy
FibroScan / transient elastography	Assesses underlying cirrhosis

High-yield: Upper GI endoscopy is the investigation of choice for varices; Doppler ultrasound is the best initial/screening test for portal vein patency and flow; HVPG is the gold standard for measuring portal pressure.

Management / Drug of Choice

Acute variceal bleed (stepwise):

1. Resuscitate (restrictive transfusion, target Hb ~7 g/dL).
2. Vasoactive drug — terlipressin / octreotide / somatostatin (start before endoscopy).
3. Prophylactic antibiotics (ceftriaxone / norfloxacin) — reduces mortality and rebleeding.
4. Endoscopic band ligation (treatment of choice) within 12 h.
5. Balloon tamponade (Sengstaken–Blakemore tube) as bridge if uncontrolled.
6. Rescue TIPS if refractory.

Prophylaxis: Non-selective beta-blocker (propranolol/carvedilol) ± endoscopic band ligation.

High-yield: Drug of choice for acute variceal bleed = terlipressin (vasopressin analogue, splanchnic vasoconstrictor) or octreotide; propranolol/carvedilol for prophylaxis; endoscopic variceal ligation is the definitive endoscopic therapy of choice over sclerotherapy.

Complications

• Variceal haemorrhage — leading cause of death; gastric (especially fundal) varices bleed more severely.
• Hepatic encephalopathy — worsened by shunts/TIPS.
• Hypersplenism — thrombocytopenia, anaemia, leucopenia.
• Spontaneous bacterial peritonitis in ascites.
• Portal hypertensive gastropathy ("mosaic"/"snake-skin" mucosa).
• Hepatorenal syndrome.

Key Differentials

Feature	Portal hypertension (caput medusae)	IVC obstruction
Centre of dilated veins	Radiate from umbilicus	Diffuse on flanks/abdomen
Direction of flow	Away from umbilicus (normal)	Always upward (groin → chest)
Associated signs	Ascites, splenomegaly, varices	Leg oedema, no splenomegaly

• Budd–Chiari syndrome (post-hepatic) vs cirrhosis (sinusoidal) — Budd–Chiari shows caudate lobe hypertrophy and hepatic vein occlusion on Doppler.
• Splenic vein thrombosis → isolated gastric varices ("left-sided/sinistral portal hypertension") with normal liver — treated by splenectomy.

High-yield: Isolated gastric (fundal) varices with a normal liver = think splenic vein thrombosis (sinistral portal hypertension), often from pancreatitis/pancreatic cancer; cure is splenectomy.

Recently asked / exam angle

• "Portal vein is formed behind the neck of the pancreas" — repeatedly asked direct fact.
• "Most posterior structure in the free margin of lesser omentum" → portal vein.
• Match the four sites of portosystemic anastomosis with their clinical features (oesophageal varices = left gastric–azygos; caput medusae = para-umbilical–epigastric; haemorrhoids = superior rectal–middle/inferior rectal).
• "Direction of blood flow in caput medusae vs IVC obstruction" — clinical reasoning MCQ.
• "TIPS connects which two veins?" → hepatic vein and portal vein; commonest complication → hepatic encephalopathy.
• "Vein draining into splenic vein" → inferior mesenteric vein (most common).
• HVPG cut-offs (>5 = PHT, ≥10 = significant, ≥12 = bleeding risk).
• "Cause of isolated gastric varices with normal liver" → splenic vein thrombosis.
• Cruveilhier–Baumgarten murmur — recanalised umbilical vein.

Rapid revision

1. Portal vein = splenic vein + SMV behind the neck of pancreas at L2; ~8 cm, no valves.
2. It is the most posterior structure in the hepatoduodenal ligament (duct anterior-right, artery anterior-left).
3. IMV usually drains into the splenic vein.
4. Portal system = capillaries at both ends (gut → hepatic sinusoids).
5. Four anastomoses: oesophagus, umbilicus, anal canal, retroperitoneum.
6. Oesophageal varices = left gastric ↔ azygos; most dangerous, cause haematemesis.
7. Caput medusae = para-umbilical (falciform lig.) ↔ epigastric veins; flow radiates away from umbilicus.
8. Haemorrhoids = superior rectal ↔ middle/inferior rectal; internal haemorrhoids above pectinate line.
9. HVPG >5 = portal HTN, ≥10 significant, ≥12 risk of bleeding/ascites.
10. Endoscopy = IOC for varices; Doppler USG = best initial; HVPG = gold standard for pressure.
11. Acute bleed DOC = terlipressin/octreotide + antibiotics + band ligation; prophylaxis = propranolol/carvedilol.
12. TIPS = hepatic vein → portal vein shunt; main complication = hepatic encephalopathy; isolated gastric varices + normal liver = splenic vein thrombosis (cure: splenectomy).