Superior vena cava, Inferior vena cava, Portal vein: Their branches and anastomoses. Need the notes for mbbs student with detailed notes from basics to advance and veins and it's all branches with images

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🩺 Complete MBBS Notes: Superior Vena Cava, Inferior Vena Cava & Portal Vein

Source: Gray's Anatomy for Students (primary), supplemented by other medical textbooks

PART 1 — SUPERIOR VENA CAVA (SVC)

1.1 Overview

The Superior Vena Cava returns deoxygenated blood from the head, neck, upper limbs, and thorax to the right atrium of the heart. It is a valveless, large-caliber vein.

1.2 Formation & Course

Feature	Detail
Formation	Junction of right + left brachiocephalic veins
Level of formation	Posterior to lower edge of right 1st costal cartilage
Termination	Right atrium — at the level of lower edge of right 3rd costal cartilage
Length	~7 cm
Orientation	Vertical
Pericardial sac	Lower half lies inside the pericardial sac (middle mediastinum)
Upper half	Superior mediastinum

📌 Key exam fact: The SVC forms part of the right superolateral border of the mediastinum on a chest X-ray.

1.3 Tributaries of the SVC

The SVC receives blood via two main roots plus additional small veins:

A. Right Brachiocephalic Vein (Innominate Vein)

Formed at junction of right internal jugular + right subclavian vein
Starts posterior to medial end of right clavicle
Passes vertically downward (short, ~2.5 cm)
Tributaries:
- Right vertebral vein
- Right 1st posterior intercostal vein
- Right internal thoracic vein
- Inferior thyroid veins
- Thymic veins

B. Left Brachiocephalic Vein (Innominate Vein)

Formed at junction of left internal jugular + left subclavian vein
Crosses the midline to the right in a slightly inferior direction (~6 cm long)
Passes posterior to the manubrium
Tributaries:
- Left vertebral vein
- Left 1st posterior intercostal vein
- Left superior intercostal vein (drains 2nd–4th left intercostal spaces)
- Left inferior thyroid vein
- Left internal thoracic vein
- Thymic and pericardial veins

⚠️ Important in children: The left brachiocephalic vein rises above the superior border of the manubrium in infants/children → less protected surgically.

C. Azygos Vein

Opens into the SVC just before it enters the pericardial sac (at ~T4 level)
The single most important tributary of the SVC that connects it to the IVC system

D. Small veins

Pericardial veins
Mediastinal veins

1.4 The Azygos System — Key Pathway for SVC

The azygos system is the collateral highway between the SVC and IVC. It is crucial for MBBS exams.

Fig. 3.105 Azygos System of Veins — Gray's Anatomy for Students

Azygos Vein (Right side)

Origin: Junction of right ascending lumbar vein + right subcostal vein (at L1/L2)
Enters thorax through aortic hiatus or posterior to right crus of diaphragm
Ascends in posterior mediastinum, to the right of thoracic duct
At T4, arches anteriorly over root of right lung → opens into SVC
Tributaries:
- Right superior intercostal vein (2nd–4th intercostal spaces)
- 5th–11th right posterior intercostal veins
- Hemiazygos vein
- Accessory hemiazygos vein
- Esophageal, mediastinal, pericardial, and right bronchial veins

Hemiazygos Vein (Left side, inferior)

Origin: Junction of left ascending lumbar vein + left subcostal vein
Ascends on the left to ~T9
Crosses vertebral column (posterior to thoracic aorta, esophagus, thoracic duct) → enters azygos vein
Tributaries: Lowest 4–5 left posterior intercostal veins, esophageal veins, mediastinal veins

Accessory Hemiazygos Vein (Left side, superior)

Descends on left from the superior posterior mediastinum to ~T8
Crosses to join azygos vein, or ends in hemiazygos vein
Tributaries: 4th–8th left posterior intercostal veins
Often connects superiorly to the left superior intercostal vein

📌 Clinical significance: If SVC is obstructed (e.g., malignancy), the azygos system enlarges to form a collateral pathway draining upper body blood directly into the IVC.

1.5 SVC Syndrome (Clinical Correlation)

Cause: Obstruction of SVC (most commonly by lung cancer or mediastinal lymphoma) Features: Facial/neck swelling, distended neck and chest veins, headache, dyspnea Collateral route: Blood drains via azygos → hemiazygos → ascending lumbar veins → IVC

1.6 Relations of SVC

Direction	Structure
Right	Right phrenic nerve, mediastinal pleura
Left	Ascending aorta
Posterior	Right pulmonary artery, right bronchus
Anterior	Thymus, pericardium

PART 2 — INFERIOR VENA CAVA (IVC)

2.1 Overview

The Inferior Vena Cava returns blood from all structures below the diaphragm to the right atrium. It is the largest vein in the body.

2.2 Formation & Course

Feature	Detail
Formation	Union of two common iliac veins
Level of formation	Level of vertebra LV, just to the right of midline
Termination	Right atrium of heart
Course	Ascends anterior to vertebral column, immediately to right of abdominal aorta
Leaves abdomen	Through IVC foramen of diaphragm (central tendon) at T8

Fig. 4.169 Inferior Vena Cava and its tributaries — Gray's Anatomy for Students

2.3 Tributaries of the IVC

From below upward (in order of drainage):

Tributary	Level	Note
Common iliac veins	L5	Right + Left unite to form IVC
Lumbar veins (1st–4th)	Various	3rd & 4th drain directly; 1st & 2nd may drain via ascending lumbar veins
Right testicular/ovarian vein	L2	Drains directly into IVC; left drains into left renal vein
Renal veins	L1–L2	Right renal vein is shorter; left is longer (crosses aorta anteriorly)
Right suprarenal vein	—	Drains directly into IVC; left suprarenal drains into left renal vein
Inferior phrenic veins	T8	Just below diaphragm
Hepatic veins	T8–T9	3 hepatic veins (right, middle, left) enter IVC just below diaphragm

⚠️ Asymmetry rule: Right testicular/ovarian vein, right suprarenal vein → drain directly into IVC. Left testicular/ovarian vein, left suprarenal vein → drain into left renal vein.

❌ What does NOT drain into IVC directly? Veins from stomach, intestines, spleen, pancreas, gallbladder — these drain into the portal system first.

2.4 Structures Crossing Anterior to IVC (Superior to Inferior)

Right common iliac artery
Root of mesentery
Right testicular/ovarian artery
Inferior part of duodenum
Head of pancreas
Superior part of duodenum
Bile duct
Portal vein
Liver (which may completely surround it)

2.5 Lumbar Veins — Special Connections

The lumbar veins are unique because they connect the IVC with the azygos system:

1st & 2nd lumbar veins → may drain into ascending lumbar veins
3rd & 4th lumbar veins → drain directly into IVC
Ascending lumbar veins (bilateral) connect:
- Below: common iliac, iliolumbar, and lumbar veins
- Above: azygos (right) and hemiazygos (left) veins in thorax

📌 Collateral significance: If IVC is blocked, the ascending lumbar veins become important collateral channels, connecting the lower body venous drainage with the upper body (SVC territory).

2.6 IVC Filter (Clinical Correlation)

Used in patients with deep vein thrombosis (DVT) when anticoagulation is contraindicated. Inserted via the SVC → right atrium → IVC, or via femoral vein approach. Catches emboli dislodged from leg/pelvic veins before they can cause pulmonary embolism.

2.7 Relations of IVC

Region	Anterior Relations
Abdominal	Liver, portal vein, head of pancreas, duodenum, root of mesentery
Posterior	Right crus of diaphragm, right renal artery, right suprarenal gland, right psoas major, right sympathetic trunk

PART 3 — PORTAL VEIN

3.1 Overview

The Portal Vein is the final common pathway for venous blood from the spleen, pancreas, gallbladder, and abdominal gastrointestinal tract to the liver. It is a unique vein because it connects two capillary beds (a portal system).

💡 Key concept: Portal blood carries absorbed nutrients + bacteria from the gut → liver for processing before entering systemic circulation.

3.2 Formation & Course

Feature	Detail
Formation	Union of superior mesenteric vein (SMV) + splenic vein
Level of formation	Posterior to neck of pancreas at vertebra LII
Length	~8 cm
Course	Ascends to the right in the free edge of lesser omentum (hepatoduodenal ligament)
Relation in lesser omentum	Posterior to bile duct (right) and hepatic artery proper (left); anterior to omental (epiploic) foramen
Termination	Divides into right and left branches entering liver parenchyma

3.3 Tributaries of the Portal Vein

A. Superior Mesenteric Vein (SMV)

Drains: Small intestine, cecum, ascending colon, transverse colon
Origin: Right iliac fossa (from terminal ileal, cecal, appendicular veins)
Ascends in mesentery, to the right of superior mesenteric artery
Unites with splenic vein posterior to neck of pancreas
Tributaries:
- Jejunal veins
- Ileal veins
- Ileocolic vein
- Right colic vein
- Middle colic vein
- Right gastro-omental (gastroepiploic) vein
- Anterior and posterior inferior pancreaticoduodenal veins

B. Splenic Vein

Formed from numerous vessels at hilum of spleen
Passes right through splenorenal ligament with splenic artery and tail of pancreas
Runs along posterior surface of body of pancreas
Unites with SMV posterior to neck of pancreas
Tributaries:
- Short gastric veins (from fundus and left greater curvature)
- Left gastro-omental (gastroepiploic) vein
- Pancreatic veins (body and tail)
- Inferior mesenteric vein (usually drains into splenic vein)

C. Inferior Mesenteric Vein (IMV)

Drains: Rectum, sigmoid colon, descending colon, splenic flexure
Begins as superior rectal vein
Receives: Sigmoid veins, left colic vein
Usually joins splenic vein (occasionally at SMV-splenic junction, or into SMV directly)

D. Direct Tributaries of Portal Vein

Right and left gastric veins (from lesser curvature of stomach and abdominal esophagus)
Cystic veins (from gallbladder)
Para-umbilical veins (run with obliterated umbilical vein in falciform ligament; connect to anterior abdominal wall veins)
Posterior superior pancreaticoduodenal vein (usually drains directly into portal vein)

3.4 Portal Vein Diagram

Portal Vein and its tributaries — Gray's Anatomy for Students

Fig. 4.134 Portal Vein, Portosystemic Anastomoses, and Tributaries — Gray's Anatomy for Students

PART 4 — PORTOSYSTEMIC ANASTOMOSES ⭐⭐⭐

This is the most exam-important section. Portosystemic anastomoses are sites where the portal venous system communicates with the systemic venous system. Normally these are small; in portal hypertension they enlarge to form varices.

4.1 The Three Major Sites

Site	Portal Vessel	Systemic Vessel	Varix Formed
Gastroesophageal junction	Left gastric vein (+ tributaries)	Tributaries of azygos system (esophageal veins → SVC)	Esophageal varices
Anorectal junction	Superior rectal vein (from IMV)	Middle and inferior rectal veins (→ internal iliac → IVC)	Anorectal varices (≠ hemorrhoids)
Umbilicus (anterior abdominal wall)	Para-umbilical veins (along ligamentum teres)	Superficial epigastric veins → superior epigastric (SVC) + inferior epigastric (IVC)	Caput medusae

4.2 Minor / Additional Anastomotic Sites

Site	Portal	Systemic
Bare area of liver	Portal branches in liver	Phrenic veins (→ IVC)
Posterior abdominal wall	Colic veins, mesenteric veins	Renal, gonadal, lumbar veins (retroperitoneal veins of Retzius) → IVC
Gastric fundus (short gastric)	Short gastric veins (via splenic)	Left renal vein via splenorenal shunt
Patent ductus venosus	Left branch of portal vein	IVC (rare, embryological remnant)

4.3 Clinical Features of Portal Hypertension

Normal portal pressure: 5–10 mmHg Portal hypertension: > 12 mmHg (clinically significant)

Triad of consequences:

Splenomegaly (increased pressure in splenic venules → spleen enlarges)
Ascites (increased hydrostatic pressure + reduced oncotic pressure from hepatic failure)
Portosystemic varices (at the anastomotic sites above)

Varices and their clinical names:

Esophageal varices → risk of torrential, potentially fatal upper GI bleed
Caput medusae → dilated veins radiating from umbilicus (flow is away from umbilicus — this distinguishes it from IVC obstruction where flow is upward)
Anorectal varices → lower GI bleed (distinguish from hemorrhoids which are anal cushions)

PART 5 — COLLATERAL CIRCULATION SUMMARY TABLE

Obstruction	Collateral Route	Clinical Sign
SVC obstruction	SVC → azygos → hemiazygos → ascending lumbar → IVC	SVC syndrome (face/neck swelling, collateral veins on chest)
IVC obstruction	IVC → ascending lumbar veins → azygos/hemiazygos → SVC	Dilated superficial abdominal/back veins; flow is upward
Portal hypertension	Portal → esophageal/gastric varices → azygos → SVC	Hematemesis, caput medusae, anorectal varices

PART 6 — QUICK REVISION MNEMONICS

Tributaries of IVC (below to above):

"Carefully Look, Really, Some Important Hepatic Veins"

Common iliac veins
Lumbar veins
Right testicular/ovarian vein
Renal veins
Suprarenal (right) vein
Inferior phrenic veins
Hepatic veins

Portal Vein Tributaries:

"Some Surgeons In India Love Cutting Patients"

Splenic vein (with IMV usually)
SMV (superior mesenteric vein)
Inferior mesenteric vein
Left & right Gastric veins
Cystic veins
Para-umbilical veins

3 Portosystemic Anastomoses (most tested):

"GOA"

Gastroesophageal junction → Esophageal varices
Ombilicus → Caput medusae
Anorectal junction → Anorectal varices

PART 7 — EXAM HIGH-YIELD SUMMARY

Question	Answer
Level of SVC formation	Lower edge of right 1st costal cartilage
SVC terminates at	Lower edge of right 3rd costal cartilage
Level of IVC formation	Vertebra LV
Level IVC leaves abdomen	T8 (central tendon of diaphragm)
IVC formed by	Right + left common iliac veins
Portal vein formed by	SMV + Splenic vein
Level of portal vein formation	LII (posterior to neck of pancreas)
Portal vein length	~8 cm
Why no valves in portal vein?	Allows bidirectional flow in response to pressure changes
Left gonadal vein drains into	Left renal vein (not IVC)
Left suprarenal vein drains into	Left renal vein (not IVC)
Which half of SVC is in pericardial sac?	Lower half
Azygos vein drains into	SVC (at T4 level)
SVC syndrome most common cause	Lung cancer (bronchogenic carcinoma)
Caput medusae flow direction	Away from umbilicus (portal hypertension)
IVC obstruction abdominal vein flow	Upward (toward SVC)

Sources: Gray's Anatomy for Students; Braunwald's Heart Disease; Schwartz's Principles of Surgery; Yamada's Textbook of Gastroenterology — all via the Medical Textbook LibraryYour credits are exhausted. Your daily credits reset tomorrow, or you can purchase a top-up for more.

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I now have all content needed. Here are the complete, detailed MBBS notes:

🩺 MBBS Anatomy Notes: Superior Vena Cava · Inferior Vena Cava · Portal Vein

Branches, Tributaries & Anastomoses — Basics to Advanced

Primary source: Gray's Anatomy for Students · Gray's Anatomy for Students, Braunwald's Heart Disease, Schwartz's Principles of Surgery

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PART 1: SUPERIOR VENA CAVA (SVC)

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📌 What is the SVC?

The Superior Vena Cava (SVC) is a large, valveless vein that collects deoxygenated blood from the head, neck, both upper limbs, and thorax and returns it to the right atrium of the heart.

1.1 Formation & Course

SVC formation — Right and left brachiocephalic veins joining to form the SVC, with azygos vein visible

Fig. 3.91 — Superior Mediastinum with Thymus Removed, showing SVC formation from brachiocephalic veins. — Gray's Anatomy for Students

Feature	Detail
Formed by	Union of right + left brachiocephalic veins
Level of origin	Posterior to lower edge of right 1st costal cartilage (near right sternal border)
Level of termination	Lower edge of right 3rd costal cartilage → right atrium
Length	~7 cm
Location	Upper → superior mediastinum; Lower half → middle mediastinum (inside pericardial sac)
Valves	None (valveless)
CXR appearance	Forms right superolateral border of mediastinum

⭐ Exam Pearl: The lower half of SVC is intrapericardial (middle mediastinum). The azygos vein opens into the SVC just before it enters the pericardial sac.

1.2 Tributaries of the SVC

The SVC has 2 main roots (the brachiocephalic veins) + the azygos vein + small mediastinal tributaries.

▶ ROOT 1: RIGHT BRACHIOCEPHALIC VEIN

Formation: Junction of right internal jugular vein (IJV) + right subclavian vein, behind the right sternoclavicular joint (medial end of right clavicle)
Course: Short (~2.5 cm), vertical descent
Tributaries:
- Right vertebral vein
- Right 1st posterior intercostal vein
- Right internal thoracic vein
- Right inferior thyroid vein
- Thymic veins

▶ ROOT 2: LEFT BRACHIOCEPHALIC VEIN

Formation: Junction of left IJV + left subclavian vein, behind medial end of left clavicle
Course: ~6 cm, crosses obliquely to the right behind the manubrium, in a slightly inferior direction
Tributaries:
- Left vertebral vein
- Left 1st posterior intercostal vein
- Left superior intercostal vein (drains 2nd–4th left intercostal spaces)
- Left inferior thyroid vein
- Left internal thoracic vein
- Thymic and pericardial veins

⚠️ Surgical note in children: In infants/children, the left brachiocephalic vein rises above the manubrium → less protected from injury during neck procedures.

▶ AZYGOS VEIN (Major tributary at T4)

The azygos vein opens into the posterior aspect of the SVC just before the SVC enters the pericardial sac (~T4 level). It is the crucial bridge between SVC and IVC territories.

▶ Other small tributaries

Pericardial veins
Mediastinal veins

1.3 Left Superior Intercostal Vein (Important!)

Drains 2nd, 3rd (and sometimes 4th) posterior intercostal veins + left bronchial veins
Passes over the left side of the aortic arch, lateral to left vagus nerve, medial to left phrenic nerve
Opens into left brachiocephalic vein
May connect inferiorly with the accessory hemiazygos vein

1.4 THE AZYGOS SYSTEM — The Bridge between SVC and IVC

The azygos system is the most important collateral pathway in the body. It connects the IVC below with the SVC above via posterior intercostal veins.

Azygos System of Veins — showing azygos, hemiazygos, accessory hemiazygos, ascending lumbar veins, and IVC

Fig. 3.105 — Azygos System of Veins — Gray's Anatomy for Students

AZYGOS VEIN (Right side — main trunk)

Feature	Detail
Origin	Junction of right ascending lumbar vein + right subcostal vein at L1/L2
Entry to thorax	Through aortic hiatus or posterior to right crus of diaphragm
Ascent	Right side of posterior mediastinum, to the right of thoracic duct
Terminates	Arches over root of right lung at T4 → enters SVC
Tributaries	Right superior intercostal vein (2nd–4th spaces); 5th–11th right posterior intercostal veins; hemiazygos vein; accessory hemiazygos vein; esophageal, mediastinal, pericardial, and right bronchial veins

HEMIAZYGOS VEIN (Left side, inferior)

Feature	Detail
Origin	Junction of left ascending lumbar vein + left subcostal vein; may connect to left renal vein
Entry to thorax	Through left crus of diaphragm
Ascent	Left posterior mediastinum to T9
Termination	Crosses vertebral column (behind thoracic aorta, esophagus, thoracic duct) → azygos vein
Tributaries	Lowest 4–5 left posterior intercostal veins; esophageal veins; mediastinal veins

ACCESSORY HEMIAZYGOS VEIN (Left side, superior)

Feature	Detail
Course	Descends left side of posterior mediastinum to T8
Termination	Crosses to join azygos vein or hemiazygos vein; connects superiorly to left superior intercostal vein
Tributaries	4th–8th left posterior intercostal veins; left bronchial veins

1.5 Relations of SVC

Direction	Structure
Right	Right phrenic nerve, mediastinal pleura, right lung
Left	Ascending aorta
Posterior	Right pulmonary artery, right bronchus
Anterior	Thymus, pericardium

1.6 Clinical: SVC Syndrome

Feature	Detail
Cause	Obstruction of SVC — most commonly bronchogenic carcinoma (right upper lobe) or mediastinal lymphoma
Features	Facial/neck/arm edema, distended neck veins, dilated chest wall veins, dyspnea, headache, blurred vision
Collateral route	Azygos → hemiazygos → ascending lumbar veins → IVC
Emergency Rx	Radiotherapy, stenting, chemotherapy depending on cause

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PART 2: INFERIOR VENA CAVA (IVC)

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📌 What is the IVC?

The IVC is the largest vein in the body. It returns blood from all structures below the diaphragm to the right atrium.

2.1 Formation & Course

Inferior Vena Cava with all tributaries — hepatic veins, renal veins, gonodal veins, inferior phrenic, common iliac

Fig. 4.169 — Inferior Vena Cava — Gray's Anatomy for Students

Feature	Detail
Formation	Union of right + left common iliac veins
Level of formation	Vertebra LV, just to the right of midline
Course	Ascends on anterior surface of vertebral column, immediately to right of abdominal aorta
Exits abdomen	Pierces central tendon of diaphragm at T8 (IVC foramen)
Terminates	Right atrium of heart
Valves	None (in the main trunk)

2.2 Tributaries of the IVC (from below upward)

No.	Tributary	Level	Notes
1	Common iliac veins (R + L)	L5	Unite to form IVC
2	Lumbar veins (3rd & 4th)	Various	Drain directly into IVC
3	Right testicular/ovarian vein	L2	Drains directly; left side → left renal vein
4	Renal veins (R + L)	L1–L2	Left renal vein longer (crosses aorta anteriorly)
5	Right suprarenal vein	—	Drains directly; left side → left renal vein
6	Inferior phrenic veins	T8	Just below diaphragm
7	Hepatic veins (3: R, M, L)	T8–T9	Enter IVC just below diaphragm

🔴 Critical asymmetry — always asked in exams:

Right gonadal vein → IVC directly

Left gonadal vein → left renal vein → IVC

Right suprarenal vein → IVC directly

Left suprarenal vein → left renal vein → IVC

❌ What does NOT drain into IVC? Gut, spleen, pancreas, gallbladder — all go to the portal vein first.

2.3 Structures Crossing the ANTERIOR Surface of IVC

(From below upward — memorise for surgery/radiology)

Right common iliac artery
Root of mesentery
Right testicular/ovarian artery
Inferior part of duodenum (3rd part)
Head of pancreas
Superior part of duodenum (1st part)
Bile duct
Portal vein
Liver (may completely surround IVC)

2.4 Lumbar Veins — The IVC–SVC Bridge

The lumbar veins are unique because they form the ascending lumbar veins, which link the IVC to the azygos/hemiazygos system:

Lumbar Vein	Drainage
5th lumbar vein	→ iliolumbar vein → common iliac vein
3rd & 4th lumbar veins	→ directly into IVC
1st & 2nd lumbar veins	→ ascending lumbar veins
Ascending lumbar veins	Connect upward to azygos (right) and hemiazygos (left) in thorax

📌 If IVC is blocked, the ascending lumbar veins enlarge and carry blood up to the azygos → SVC system — a critical collateral pathway.

2.5 Relations of IVC

Region	Anterior	Posterior
Abdominal	Liver, portal vein, head of pancreas, duodenum, root of mesentery	Right crus of diaphragm, right renal artery, right suprarenal gland, right psoas major
Right lateral	Right ureter, right renal artery	—
Left	Abdominal aorta	—

2.6 Clinical: IVC Obstruction

Causes: Thrombosis, tumour compression (RCC, HCC), retroperitoneal fibrosis

Collateral routes:

Ascending lumbar veins (retroperitoneal) → azygos/hemiazygos → SVC
Superficial epigastric veins → thoracoepigastric vein → lateral thoracic vein → axillary → SVC
Paravertebral venous plexus

📌 In IVC obstruction — dilated superficial abdominal wall veins with flow going upward (toward SVC). Compare: in SVC obstruction, flow is downward. In portal hypertension (caput medusae), flow is away from umbilicus in all directions.

2.7 Clinical: IVC Filter

Used in DVT patients when anticoagulation is contraindicated
Inserted via femoral vein or via SVC → right atrium → IVC
Traps emboli from lower limb/pelvic DVT before they cause pulmonary embolism

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PART 3: PORTAL VEIN

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📌 What is the Portal Vein?

The portal vein is the final common pathway for venous blood from the spleen, pancreas, gallbladder, and abdominal gastrointestinal tract to the liver. It is a portal system — connecting two capillary beds (gut capillaries → liver sinusoids).

💡 Portal blood carries absorbed nutrients + toxins + bacteria from the gut to the liver for processing before entering systemic circulation.

3.1 Formation & Course

Portal vein formation from SMV and splenic vein, showing all tributaries

Fig. 4.132/133 — Portal Vein and Tributaries — Gray's Anatomy for Students

Feature	Detail
Formation	Union of Superior Mesenteric Vein (SMV) + Splenic vein
Level	Posterior to neck of pancreas, at vertebra LII
Length	~8 cm
Ascent	Passes posterior to superior part of duodenum → enters free edge of lesser omentum (hepatoduodenal ligament)
Contents of hepatoduodenal ligament	Portal vein (posterior), Bile duct (right anterior), Hepatic artery proper (left anterior) — "BPA" mnemonic
Omental foramen	Portal vein is anterior to it
Termination	Divides into right and left branches at porta hepatis → enter liver
Valves	None

⭐ Exam Pearl: Portal vein is posterior in the hepatoduodenal ligament. Bile duct is right anterior, hepatic artery is left anterior — Together = "BPA" from right to left anteriorly (or: "Happy Americans Buy Porsches" = Hepatic Artery, Bile duct, Portal vein — right to left).

3.2 All Tributaries of the Portal Vein

The portal vein drains through 2 main roots + direct tributaries:

▶ ROOT 1: SUPERIOR MESENTERIC VEIN (SMV)

Drains: Small intestine (jejunum, ileum), cecum, appendix, ascending colon, transverse colon
Origin: Right iliac fossa — formed by junction of terminal ileal, cecal, and appendicular veins
Course: Ascends in mesentery to the right of superior mesenteric artery (SMA)
Unites with: Splenic vein posterior to neck of pancreas

Tributaries of SMV:

Tributary	Drains
Jejunal veins	Jejunum
Ileal veins	Ileum
Ileocolic vein	Terminal ileum, cecum, appendix
Right colic vein	Ascending colon
Middle colic vein	Transverse colon
Right gastro-omental vein	Right part of greater curvature of stomach
Anterior and posterior inferior pancreaticoduodenal veins	Head of pancreas, duodenum

▶ ROOT 2: SPLENIC VEIN

Origin: Numerous vessels from hilum of spleen
Course: Passes right through splenorenal ligament with splenic artery and tail of pancreas → runs along posterior surface of body of pancreas → unites with SMV

Tributaries of Splenic vein:

Tributary	Drains
Short gastric veins	Fundus and left greater curvature of stomach
Left gastro-omental vein	Greater curvature of stomach (left part)
Pancreatic veins	Body and tail of pancreas
Inferior mesenteric vein (usually)	Rectum, sigmoid, descending colon, splenic flexure

▶ INFERIOR MESENTERIC VEIN (IMV)

Drains: Rectum (via superior rectal vein), sigmoid colon, descending colon, splenic flexure
Begins as: Superior rectal vein
Receives: Sigmoid veins, left colic vein
Termination: Usually into splenic vein (occasionally at SMV–splenic junction or into SMV)

▶ DIRECT TRIBUTARIES of Portal Vein (small)

Tributary	Drains
Right gastric vein	Lesser curvature of stomach (right) + lower esophagus
Left gastric vein (coronary vein)	Lesser curvature of stomach (left) + lower esophagus — ⭐ KEY in portal HTN
Cystic veins	Gallbladder
Para-umbilical veins	Run in falciform ligament with obliterated umbilical vein → connect to abdominal wall veins
Posterior superior pancreaticoduodenal vein	Usually empties directly into portal vein

3.3 Portal Vein Diagram — Full System

Portal vein tributaries diagram showing portal vein, splenic vein, SMV, IMV, gastric veins, caput medusae, IVC connections

Fig. 4.134 — Portosystemic Anastomoses — Gray's Anatomy for Students

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PART 4: PORTOSYSTEMIC ANASTOMOSES ⭐⭐⭐

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📌 What are Portosystemic Anastomoses?

These are sites where the portal venous system communicates with the systemic venous system. Normally they carry minimal flow. In portal hypertension (portal pressure > 12 mmHg), they dilate massively to form varices — which can bleed catastrophically.

4.1 Three MAJOR Sites (Must Know for Exams)

#	Site	Portal Side	Systemic Side	Varix Name	Clinical Risk
1	Gastroesophageal junction	Left gastric vein (coronary vein) + tributaries	Esophageal tributaries → azygos system → SVC	Esophageal varices	💀 Life-threatening UGI bleed
2	Anorectal junction	Superior rectal vein (from IMV → portal)	Middle & inferior rectal veins → internal iliac → IVC	Anorectal varices	Lower GI bleed
3	Umbilicus (anterior abdominal wall)	Para-umbilical veins (along ligamentum teres/falciform ligament → left branch of portal vein)	Superficial + inferior epigastric veins → superior epigastric (SVC) + inferior epigastric (IVC)	Caput medusae	Cosmetic; massive varices rare

4.2 Additional Anastomotic Sites

Site	Portal vessel	Systemic vessel
Bare area of liver	Small portal branches in liver	Inferior phrenic veins → IVC
Retroperitoneum	Colic, mesenteric veins	Renal, gonadal, lumbar veins (Retzius veins) → IVC
Falciform ligament	Left portal vein branch	Inferior epigastric / internal thoracic veins

4.3 Clinical Features of Portal Hypertension

Normal portal pressure: 5–10 mmHg Portal hypertension: > 12 mmHg (clinically significant)

Classic triad:

Splenomegaly (back-pressure → splenic venous congestion)
Ascites (raised hydrostatic pressure + reduced albumin from liver failure)
Portosystemic varices

Named varices:

Esophageal varices — risk of torrential, potentially fatal haematemesis (most dangerous)
Caput medusae — dilated veins radiating from umbilicus; flow is away from umbilicus in all directions
Anorectal varices — bleeding per rectum (NOT hemorrhoids, which are anal cushions)

CT scan showing esophageal varices and caput medusae from portal hypertension in cirrhosis

CT Portal Venography: (A) Dilated esophageal/gastric varices; (B) Caput medusae — recanalized umbilical vein with periumbilical varices in cirrhosis

4.4 Distinguishing Caput Medusae vs IVC Obstruction

Feature	Caput Medusae (Portal HTN)	IVC Obstruction
Blood flow in abdominal veins	Away from umbilicus (all directions)	Upward (from groin toward chest)
Mechanism	Portal → para-umbilical → abdominal wall veins	Collateral bypass for blocked IVC
Umbilicus involved	Yes (epicentre)	No
Splenomegaly	Yes	No
Leg edema	Mild	Severe

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PART 5: COLLATERAL CIRCULATION SUMMARY

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Obstruction	Main Collaterals	Clinical Consequence
SVC obstruction	Azygos → hemiazygos → ascending lumbar → IVC	SVC syndrome (face/neck swelling, dilated chest veins)
IVC obstruction	Ascending lumbar → azygos/hemiazygos → SVC; or superficial epigastric veins	Leg edema, dilated abdominal veins (flow upward)
Portal hypertension	Para-umbilical; esophageal varices via left gastric → azygos; anorectal varices	Caput medusae, hematemesis, rectal bleeding

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PART 6: MNEMONICS & QUICK REVISION ⭐

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IVC Tributaries (below → above):

"Come Let's Run, Really Super Incredible Heroes"

Common iliac veins
Lumbar veins
Right gonadal vein (testicular/ovarian)
Renal veins
Suprarenal (right) vein
Inferior phrenic veins
Hepatic veins

Portal Vein Direct Tributaries:

"Right Gyms Cause Parachute Crashes"

Right & left Gastric veins
Cystic veins
Para-umbilical veins
(+ SMV and Splenic vein as main roots)

Hepatoduodenal ligament contents (right → left):

"Bill And Pam"

Bile duct (right)
A = hepatic Artery proper (left)
Portal vein (posterior)

3 Portosystemic Anastomoses:

"GAU" (or "Good Anatomy Understanding")

Gastroesophageal → esophageal varices
Anorectal → anorectal varices
Umbilicus → caput medusae

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PART 7: HIGH-YIELD EXAM TABLE ⭐

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Question	Answer
SVC is formed by	R + L brachiocephalic veins
Level of SVC formation	Lower edge of right 1st costal cartilage
SVC terminates at	Lower edge of right 3rd costal cartilage → right atrium
Which half of SVC is intrapericardial?	Lower half
Azygos vein opens into SVC at	T4 (just before SVC enters pericardial sac)
Azygos vein formed by	Right ascending lumbar vein + right subcostal vein (L1/L2)
IVC formed by	R + L common iliac veins
Level of IVC formation	Vertebra LV
IVC exits abdomen at	T8 (central tendon of diaphragm)
Left gonadal vein drains into	Left renal vein (not IVC directly)
Left suprarenal vein drains into	Left renal vein
Right gonadal vein drains into	IVC directly
Portal vein formed by	SMV + Splenic vein
Level of portal vein formation	LII (posterior to neck of pancreas)
Portal vein length	~8 cm
Portal vein position in hepatoduodenal ligament	Posterior
IMV usually drains into	Splenic vein
Major portosystemic anastomosis causing bleeding	Esophageal varices (left gastric → azygos)
Caput medusae flow direction	Away from umbilicus (radiates outward)
SVC syndrome most common cause	Bronchogenic carcinoma (right upper lobe)
Collateral in SVC obstruction	Azygos system
Collateral in IVC obstruction	Ascending lumbar veins
Normal portal pressure	5–10 mmHg
Portal HTN threshold	> 12 mmHg
IVC filter used for	DVT with contraindication to anticoagulation

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PART 8: EMBRYOLOGY (Brief — MBBS Level)

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Structure	Embryological Origin
SVC	Right cardinal vein system (anterior cardinal vein)
IVC	Complex — four segments from multiple veins (posterior cardinal, subcardinal, supracardinal)
Portal vein	Vitelline (omphalomesenteric) veins
Ligamentum teres hepatis (round ligament)	Obliterated umbilical vein — carries para-umbilical veins in portal HTN
Ligamentum venosum	Obliterated ductus venosus (connected left portal branch → IVC in fetus)
Persistent left SVC	Failure of obliteration of left common cardinal vein

Sources: Gray's Anatomy for Students (Mitchell, Drake, Vogl); Braunwald's Heart Disease; Schwartz's Principles of Surgery; Yamada's Textbook of GastroenterologyYour credits are exhausted. Your daily credits reset tomorrow, or you can purchase a top-up for more.

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