Portal Vein

Formation

• Gray's Anatomy for Students, p. 417
• Sabiston Textbook of Surgery, p. 1864

Course

1. Passes posterior to the superior part of the duodenum (first part of duodenum)
2. Enters the right margin of the lesser omentum (hepatoduodenal ligament)
3. Within the hepatoduodenal ligament it occupies the posterior position - with the bile duct to its right and the hepatic artery proper to its left; the vein is anterior to the omental (epiploic) foramen of Winslow
4. Ascends to the porta hepatis where it divides into right and left branches that enter the liver parenchyma

Portal Vein Anatomy Diagram (Gray's Anatomy for Students)

Tributaries

Intrahepatic Distribution

• Left portal vein: runs transversely along the base of segment IV, then bends 90° into the umbilical fissure, giving off branches to segments II, III, and IV; also supplies the left caudate lobe
• Right portal vein: shorter extrahepatic course, divides into right anterior and right posterior sectoral branches supplying the right lobe

• Sabiston Textbook of Surgery, p. 1864
• Schwartz's Principles of Surgery, p. 1376

Physiology

Portosystemic Anastomoses

• Gray's Anatomy for Students, p. 419-420
• Fischer's Mastery of Surgery, p. 5294

Portal Vein Thrombosis (PVT)

• Most common cause of prehepatic portal hypertension (~50% of cases in children)
• Chronic occlusion leads to cavernous transformation - formation of collateral vessels in/around the occluded vein
• Portal pressure in portal hypertension rises to 20-30 mmHg
• Ultrasound findings: hepatofugal flow (flow away from liver), splenomegaly, portosystemic collaterals

Portal Hypertension - Key Features

• Esophageal/gastric varices with risk of massive hemorrhage
• Splenomegaly with hypersplenism
• Ascites (from sinusoidal hypertension + hypoalbuminemia)
• Caput medusae
• Hepatic encephalopathy (portosystemic shunting of ammonia)
• Hepatorenal syndrome in advanced disease

Clinical Correlates

• Hepatoduodenal ligament content ("Portal Triad" in the free edge of lesser omentum): Portal vein (posterior), Hepatic artery proper (left/anterior), Common bile duct (right/anterior) - "Love Affair Gone Wrong" mnemonic: Left Artery, right biLe duct, posteriorly vein
• Pringle maneuver: manual compression of the hepatoduodenal ligament to control hepatic inflow during liver surgery
• TIPS (Transjugular Intrahepatic Portosystemic Shunt): creates an artificial shunt between the hepatic vein and portal vein within the liver to decompress portal hypertension
• Portal vein gas (pneumatosis portalis): seen on CT as air in the portal venous system - indicates bowel ischemia/infarction and is an ominous sign

Extrahepatic Biliary Apparatus

1. Right and Left Hepatic Ducts

• Formed within the liver parenchyma by union of segmental ducts
• They emerge from the liver and unite 0.25 to 2.5 cm from the liver surface to form the common hepatic duct
• Accessory hepatic ducts (normal segmental ducts that join the biliary tract extrahepatically rather than intrahepatically) may be present - usually with about half the diameter of the main duct; they are surgically important as they can be mistaken for the cystic duct

2. Common Hepatic Duct (CHD)

• Formed by union of right and left hepatic ducts
• Usually less than 2.5 cm long
• Runs in the free edge of the lesser omentum (hepatoduodenal ligament)
• Becomes the common bile duct when joined by the cystic duct

3. Gallbladder

Parts

Relations

• Posteriorly: rests on Gerota's fascia of the right kidney
• Inferiorly: related to the duodenum and hepatic flexure of colon

Blood Supply

• Cystic artery - most commonly a branch of the right hepatic artery, arising posterior to the common hepatic duct; bifurcates into anterior (superficial) and posterior (deep) branches at the neck
• In 15% of cases the right hepatic artery and/or cystic artery cross in front of the common hepatic duct - a surgically important variant

Venous Drainage

• Anterior and posterior cystic veins drain the gallbladder; they follow the cystic artery and then drain directly into the cystic plate, connecting to the middle hepatic vein within the intrahepatic parenchyma

Nerve Supply

• Sympathetic: from the 9th thoracic segment and celiac plexus; the right phrenic nerve also contributes (explains referred pain to the right shoulder tip in cholecystitis)
• Parasympathetic: hepatic branch of the anterior vagus nerve

Function

• Stores and concentrates bile during fasting (sphincter of Oddi closed → bile fills gallbladder)
• Cholecystokinin (CCK) released with enteral feeding causes gallbladder contraction + sphincter of Oddi relaxation → bile bolus delivered to duodenum
• Main function of bile: emulsification of ingested fats to allow pancreatic lipase action

Lymphatic Drainage

4. Cystic Duct

• Connects gallbladder neck to the common hepatic duct
• Contains the spiral valve of Heister (spirally arranged mucosal folds that prevent sudden emptying or overfilling)
• Joins the CHD to form the CBD in the supraduodenal segment of CHD in 80% of cases
• Variable junction: may join as low as the retroduodenal or retropancreatic part; occasionally joins the right hepatic duct or a right sectoral duct

Cystic Duct Variations

5. Common Bile Duct (CBD)

• Formed by union of the cystic duct + common hepatic duct
• Length: approximately 7.5 cm; mean diameter: ~6 mm (may dilate significantly with distal obstruction)
• Divided into four parts:

Blood Supply to the Bile Duct

• Supraduodenal CBD: small branches from the cystic artery (from above) and gastroduodenal/retroduodenal artery (from below) - forming an axial blood supply running at 3 o'clock and 9 o'clock positions along the duct
• Retroduodenal CBD: branches from the gastroduodenal and retroduodenal arteries
• This axial supply is vulnerable during high bile duct injury, leading to ischemic strictures

6. Hepatopancreatic Ampulla (Ampulla of Vater) and Sphincter of Oddi

• Outside the duodenal wall (most common) - they then travel together through the wall
• At the ampulla itself
• Independently, opening separately on the papilla (when a complete septum is present)

• Choledochal sphincter: surrounds the terminal CBD - the main regulator of bile flow into the duodenum
• Sphincter of the hepatopancreatic ampulla: surrounds the ampulla itself

7. Triangle of Calot (Hepatocystic Triangle)

• Inferiorly - cystic duct
• Medially - common hepatic duct
• Superiorly - superior border of the cystic artery

• Superiorly - inferior surface of the liver
• Laterally - cystic duct and medial border of gallbladder
• Medially - common hepatic duct

Summary Diagram

Ischiorectal (Ischioanal) Fossa

Nomenclature note: The term ischioanal fossa is now preferred over ischiorectal fossa in modern anatomy, as the space is related to the anal canal - not directly to the rectum. Both terms remain in clinical use.

Overview

Shape and Orientation

• The tip (apex) points superiorly, near the junction of the levator ani and obturator internus
• The base faces inferiorly, covered by perineal skin
• The tip of the pyramid points toward the pubic symphysis (anteriorly)

Boundaries

Contents

1. Fat Body of the Ischioanal Fossa

• The fossa is mainly filled with fat (the fat pad / fat body)
• This fat acts as a mobile pad that slides downward and backward during bowel evacuation and during labor - allowing the anal canal to distend
• The fat is loose and areolar, making it easily displaced and able to accommodate large abscesses

2. Pudendal Canal (Alcock's Canal) - Key Structure

• Formation: formed by a duplication/fold of the obturator internus fascia
• Course: begins just below the ischial spine → courses along the lateral wall of the ischioanal fossa below the tendinous arch of the levator ani → passes toward the pubic symphysis
• Entry: neurovascular structures exit the lesser pelvis through the greater sciatic foramen, loop around the ischial spine/sacrospinous ligament, and re-enter the perineum through the lesser sciatic foramen into the pudendal canal

• Internal pudendal artery
• Internal pudendal vein(s)
• Pudendal nerve (S2-S4)

3. Inferior Rectal (Inferior Anal) Vessels and Nerve

• The inferior rectal vessels and inferior rectal nerve (branch of pudendal nerve) cross the fossa transversely from the pudendal canal to reach the external anal sphincter and perianal skin
• They traverse the fat of the ischioanal fossa

4. Perineal Branch of S4

• A small nerve crossing the fossa contributing to innervation of the external sphincter

Transverse Section Diagram

Communication Between the Two Fossae

• Deep postanal space (also called the retroanal space) - posterior to the anal canal, between the external sphincter and the anococcygeal ligament
• This communication is why abscesses can spread from one side to the other forming a horseshoe abscess

Clinical Significance

1. Ischiorectal (Ischioanal) Abscess

• Most common type of anorectal abscess (after perianal abscess)
• Origin: usually from cryptoglandular infection - an intersphincteric abscess that penetrates the external sphincter below the puborectalis level and expands into the fat of the ischioanal fossa
• Why it can be large and insidious: the levator ani (upper border of the fossa) slopes upward, so the abscess expands upward rather than pointing through the skin; it may be palpable as a bulge above the puborectalis but actually lies below the levator ani
• Presentation: pain, redness, and fluctuance in the perirectal/buttock region; fever; inability to sit

2. Horseshoe Abscess

• A horseshoe-shaped infection that starts in the posterior midline intersphincteric space, enters the deep postanal space (incising the anococcygeal ligament), and spreads bilaterally to involve both ischioanal fossae
• Treatment: drainage of the deep postanal space + counter-drainage incisions for each limb of the ischiorectal space

3. Anal Fistula

• An ischiorectal (trans-sphincteric) fistula has its external opening typically over the ischioanal fossa skin
• The fistula tract crosses the external sphincter

4. Pudendal Nerve Block

• Performed by anesthetizing the pudendal nerve at the level of the ischial spine - before it enters the pudendal canal - using a transvaginal or transperineal approach
• Used in obstetrics for perineal analgesia; anesthetizes the inferior rectal, perineal, dorsal clitoral/penile, and posterior labial/scrotal nerves

5. Surgical Caution

• The internal pudendal vessels and pudendal nerve in the lateral wall of the fossa are at risk during ischiorectal abscess drainage; incisions should be kept medial (closer to the anal canal) to avoid injury

Summary Table

Kidney

Overview

Gross Anatomy

Size, Weight, and Position

Internal Structure

Cortex (Outer)

• Granular-appearing outer zone
• Contains the glomeruli, proximal convoluted tubules, distal convoluted tubules, and columns of Bertin (cortical tissue projecting between pyramids)

Medulla (Inner)

• Striated inner zone; divided into 8-18 renal pyramids
• Each pyramid is a cone with:
  • Base at the corticomedullary junction
  • Apex (papilla) pointing toward the renal pelvis
• Contains loops of Henle and collecting ducts
• Papillary ducts (~20 per papilla) open at the area cribrosa on the papillary tip
• Columns of Bertin are cortical invaginations that separate adjacent pyramids

Collecting System

Coverings (from inside out)

1. Fibrous capsule - thin, tough; strips easily from a healthy kidney
2. Perirenal fat (perinephric fat) - fine, light yellow; fills the perirenal space
3. Gerota's fascia (renal fascia) - surrounds the kidney + adrenal gland + perirenal fat
   • Anterior lamina = fascia of Toldt (prerenal fascia)
   • Posterior lamina = fascia of Zückerkandl (retrorenal fascia)
   • The two laminae merge laterally to form the lateroconal fascia
   • Medially: continuous with adventitia of aorta, IVC, and renal vessels
   • Superiorly: closed (fused above the adrenal)
   • Inferiorly: open (cone-shaped opening into extraperitoneal pelvis) - explains how perirenal collections can track inferiorly
4. Paranephric (pararenal) fat - coarser, yellow-orange; external to Gerota's fascia; most prominent posteriorly

Clinical note: Gerota's fascia contains perinephric fluid collections (urinoma, hematoma, abscess) and is used as the plane of dissection in radical nephrectomy.

Relations

Posterior Relations

Anterior Relations

Medial Relations (both sides)

• Right: Right adrenal gland (superomedial), IVC, duodenum
• Left: Left adrenal gland (superomedial), aorta, tail of pancreas

Blood Supply

Renal Artery

• Arises from the abdominal aorta at L1-L2
• Right renal artery is longer and passes posterior to the IVC, right renal vein, head of pancreas, and descending duodenum
• Left renal artery is shorter; passes posterior to the left renal vein and body of pancreas
• Each renal artery divides at the hilum into:
  • Anterior division (larger): gives 3-4 segmental arteries supplying upper, middle, lower + apical segments
  • Posterior division (smaller): supplies posterior segment (>50% of posterior surface)

Intrarenal Arterial Hierarchy

Renal artery
  → Segmental (lobar) arteries
    → Interlobar arteries (in columns of Bertin)
      → Arcuate arteries (at corticomedullary junction)
        → Interlobular (radial) arteries (through cortex)
          → Afferent arterioles → Glomerular capillaries
            → Efferent arterioles → Peritubular capillaries (cortex)
                                  → Vasa recta (medulla)

• Glomerular capillary pressure: ~60 mmHg (drives filtration)
• Peritubular capillary pressure: ~13 mmHg (drives reabsorption)

Renal Vein

• The left renal vein is longer (~7.5 cm vs ~2.5 cm right); crosses anterior to the aorta
• Left renal vein receives: left gonadal vein (inferiorly), left suprarenal vein (superiorly), and left inferior phrenic vein
• Right gonadal and right suprarenal veins drain directly into the IVC

Renal Blood Flow

• ~22% of cardiac output (~1100 mL/min in adults)
• Cortex receives ~90% of total renal blood flow

The Nephron - Functional Unit

Nephron Types

• Cortical nephrons (~85%): short loops of Henle, peritubular capillaries
• Juxtamedullary nephrons (~15%): long loops extending deep into medulla; associated with vasa recta - critical for urinary concentration

Lymphatic Drainage

• Renal lymphatics follow the renal vessels
• Drain to lateral aortic (para-aortic) lymph nodes at the level of L1-L2
• Important in staging of renal cell carcinoma

Nerve Supply

• Sympathetic: from T10-L1 via the celiac and renal plexuses; vasomotor (vasoconstriction of afferent arterioles); pain fibers
• Parasympathetic: vagus nerve (minor functional role)
• Referred pain from the kidney: loin to groin (T10-L1 dermatomes); upper ureteric colic → anterior abdominal wall; lower ureteric colic → scrotum/labia

Juxtaglomerular Apparatus (JGA)

• Juxtaglomerular (granular) cells - modified smooth muscle cells of the afferent arteriole; secrete renin
• Macula densa - specialised cells of the thick ascending limb / early distal tubule; detect tubular NaCl concentration
• Extraglomerular mesangial (Lacis) cells

Key Clinical Correlates