Liver, Biliary System, and Pancreas Anatomy

Liver, Biliary System, and Pancreas

Liver Anatomy

• Location, Measurements, and Size
  • Lies beneath the right costal margin, in the right hypochondrium, epigastrium, and into the left hypochondrium.
  • Superiorly: Dome of diaphragm
  • Posteriorly: Bony lumbar region.
  • Right Lobe Measurement (Midclavicular line): 13-17 cm
  • Liver Size (weight):
    • Adult males: 1400-1800 g
    • Adult females: 1200-1400 g
• Gross Anatomy
  • Occupies almost all of the RT hypochondrium, greater part of epigastrium and left hypochondrium as far as the mammillary line.
  • Contour and shape can vary.
  • Lies inferior to the diaphragm.
  • Ribs cover greater portion of RT lobe.
  • LT lobe extends several centimeters below the xiphoid process.
  • Most of LT lobe covered by rib cage
  • Fundus of the stomach lies posterior and lateral to the LT lobe
  • Duodenum lies adjacent to the RT lobe and medial segment of the LT lobe.
  • Body of pancreas is usually just inferior to LT lobe.
  • Posterior border of liver contacts the RT kidney, IVC, and AO.
  • The diaphragm covers the superior border of the liver.
  • Posterior borders are in contact with the IVC, gallbladder (GB), cystic duct, portal vein (PV) confluence, hepatic artery (HA), RT kidney, and colon.
  • Projections can be altered by disease (tumor infiltration, cirrhosis, subphrenic abscess displacing inferiorly).
  • Ascites, tumors can elevate the liver.
• Inferior (Visceral) Surface Indentations
  • Rt-sided:
    • Right hepatic flexure of colon
    • Right kidney/adrenal gland
    • First portion of duodenum
    • Gallbladder
  • Lt-sided:
    • Gastric indentation
    • IVC groove (posterior)
    • Anterior mid portion (medial portion of left lobe) → quadrate lobe
    • Left lateral boundary: falciform ligament.
    • Posterior midportion (below porta hepatis) → caudate lobe
• Lobes of the Liver
  • Divided into 4 anatomic lobes:
    1. Left
    2. Right
    3. Caudate
    4. Quadrate
• Rt Lobe
  • Six times larger than LT lobe.
  • Has 2 segments: anterior and posterior, separated horizontally by the RHV.
  • Anatomically separated from Left lobe by Falciform ligament and Main Lobar Fissure (MLF) on anterior surface.
  • Functionally, the MHV divides the medial segment of LT lobe from the anterior segment of RT lobe.
  • Riedel’s lobe - extension of the posterior segment of RT lobe that can extend to iliac crest
• Lt Lobe
  • Left intersegmental fissure divides Left lobe into medial and lateral segments.
  • Intersegmental fissure is marked on external liver margin by the Falciform ligament.
  • LHV runs horizontally between the medial and lateral segments.
  • Left lobe is bound posterior by the Porta Hepatis, medially by the GB fossa and laterally by the fossa for Umbilical vein
  • Two fissures:
    • Ligamentum Teres (Round ligament)
    • Ligamentum Venosum
      • fibrous remnant of fetal circulation in which the umbilical vein is connected to IVC, in adulthood it is usually seen attached to Left branch of Portal vein within Porta hepatis (gateway to liver)
• Caudate Lobe
  • Referred to as Spiegel's lobe or segment I.
  • Located on the visceral surface, between the IVC and the Ligamentum venosum.
  • Inferiorly: Bounded by Porta hepatis
  • Posteriorly: Separated from the RT lobe by IVC
  • Left: Bounded by the fissure for the Ligamentum Venosum
  • Anteriorly: Connected to the RT lobe by the caudate process, which passes laterally between the Portal vein and the IVC at the Porta Hepatis.
• Quadrate lobe
  • Located on the inferior surface of the RT lobe.
  • Sits on the inferior surface of the RT lobe, between the anterior margin of the liver and the Porta hepatis

Liver: Ligaments and Fissures

• Liver covered by thin connective tissue layer called Glisson’s capsule
• Main Lobar Fissure (MLF) is boundary between RT and LT lobes of liver
  • With ultrasound it appears as hyperechoic line extending from portal vein to neck of GB
  • Sonographer uses this ligament as a landmark to find GB if diseased
• Falciform ligament extends from umbilicus to diaphragm and contains ligamentum teres
  • Ligamentum teres appears as a bright echogenic focus with ultrasound and is seen as rounded termination of falciform ligament
• Ligamentum venosum separates the Left lobe from caudate lobe
  • Seen on ultrasound as a thin, horizontal line just anterior to caudate lobe

Couinaud’s System of Hepatic Nomenclature

• I Caudate lobe

• II Left lateral superior

• III Left lateral inferior

• IVa Left medial superior

• IVb Left medial inferior

• V Right anterior inferior

• VI Right posterior inferior

• VII Right posterior superior

• VIII Right anterior superior

• Cantlie's line: Divides liver into right and left hemiliver (liver halves); hemilivers further divided into anterior and posterior segments

• Rex-Cantlie line: Runs from gallbladder fossa to inferior vena cava and passes through portion of caudate lobe; this is the plane we refer to for the main lobar fissure

Hepatic Vasculature

• Hepatic Artery (25-30% of supply)

• Portal Venous System (70-75% of supply)

• Hepatic Veins

  • Right hepatic is the largest and Left hepatic vein is the smallest.

• The main difference between the portal vein and hepatic veins lies in their function and direction of blood flow within the liver.

  • Portal vein
    • formed by the union of the SMV (Superior Mesenteric vein) & SV (Splenic vein)
    • delivers blood from the digestive organs to the liver for processing
    • enters the liver
  • Hepatic veins
    • drain the liver and return the blood to the heart
    • exit the liver

• Portal Triad Consists of

  1. Portal vein
  2. Hepatic artery
  3. Bile duct
  • These structures travel together, throughout liver, to support physiological function of liver
  • The portal vein is contained within a connective tissue sheath called Glisson's sheath, which contributes to its echogenicity

• LHV vs LPV

  • LHV - Left hepatic vein divides LT lobe of the liver into its medial and lateral segments.
  • LPV - Left portal vein divides LT lobe of the liver into superior and inferior segments based on its transverse plane

Hepatic Veins

• Separates and Drains the
  • Anterior and posterior segments of the right lobe: Right hepatic vein
  • Right lobe and medial left lobe: Middle hepatic vein
  • Medial and lateral segments of the left lobe: Left hepatic vein

Caudate Lobe – Vasculature

• Drained by veins that directly connect to the inferior vena cava (IVC):
  • Spieghel veins (type of extrahepatic veins)
  • Short hepatic veins
  • Emissary hepatic veins
• Supplied by multiple arteries, including branches of the
  • right hepatic artery (RHA)
  • left hepatic artery (LHA)

Sonographic Appearance of the Liver

• Parenchyma of the liver is used to sonographically evaluate other organs.
  • Kidneys equal to or less echogenic than the liver.
  • Spleen isoechoic or hyperechoic to the liver.
• Liver is used as a window to visualize abdominal structures such as pancreas, gallbladder

Biliary System Anatomy

• The biliary apparatus consists of:

  • RT and LT hepatic ducts
  • Common hepatic duct
  • Common bile duct
  • Gallbladder
  • Cystic duct.

• Each hepatic duct is formed by the union of bile canaliculi from the liver lobules.

  • RT & LT hepatic ducts unite at the Porta hepatis to form the Common Hepatic Duct (CHD)
  • CHD then joins with the Cystic duct(CD) from GB to form the Common Bile Duct (CBD), which runs parallel with Portal vein.
  • CBD is joined by the Main Pancreatic duct (MPD); together they open through a small ampulla (the ampulla of Vater) into the duodenal wall.
  • The end parts of both ducts (CBD and MPD) and the ampulla are surrounded by circular muscle fibers known as the Sphincter of Oddi.

Biliary System Anatomy Measurements

• Gallbladder (GB)
  • 8-12 cm long
  • Less than 4 cm diameter
• Gallbladder wall (GB wall) 3 mm thick
• Right and left hepatic ducts
  • 0.5-2.5 cm long (Lt > Rt)
  • 0.1-0.2 cm diameter
• Common hepatic duct (CHD)
  • 2.0-6.5 cm long
  • 0.1-0.2 cm diameter
• Common bile duct (CBD)
  • 5-15 cm long
  • 0.1-0.7 cm diameter
• Cystic duct
  • 0.5-0.8 cm long
  • 0.1-0.4 cm diameter

Cystic Duct

• Cystic Duct:
  • A short, narrow tube that carries bile from GB
  • Joins the CHD to form the CBD
• Valves of Heister:
  • AKA spiral mucosal folds
  • located on the inner surface of the Cystic duct (CD)
  • help maintain the patency of the CD, which can be narrow and tortuous
  • play a role in facilitating gallbladder emptying.

Gallbladder Location

• Gallbladder fossa
  • Posteroinferior (Rt. lobe)
  • Related to main lobar fissure

Sonographic Appearance of the Biliary System

• Gallbladder normal measurements

  • Size: <4 cm transverse, <8-12 cm longitudinal
  • Wall thickness: <3 mm
  • Lumen: Anechoic

• Divided into the fundus, body, and neck

• The rounded fundus usually projects below the inferior margin of the liver, where it encounters the anterior abdominal wall at the level of the ninth right costal cartilage.

  • The body generally lies in contact with the visceral surface of the liver and is directed upward, backward, and to the left.

• The neck becomes continuous with the cystic duct, which turns into the lesser omentum to join the right side of the common hepatic duct to form the common bile duct.

• Common Bile Duct Portal Triad

  • Portal vein posterior,
  • CBD anterior and lateral,
  • Hepatic artery anterior and medial.

• The proximal portion of CBD is lateral to HA and anterior to PV.

• Portal Triad Mickey Mouse Sign

  • Right ear – CBD
  • Left ear – HA
  • Face – PV

Pancreatic Anatomy

• Majority - lies in the retroperitoneal cavity, except for a small portion of the head

• Posterior structures:

  • connective prevertebral tissues ,
  • portal-splenic confluence ,
  • superior mesenteric vessels ,
  • aorta,
  • inferior vena cava,
  • lower border of the diaphragm

• Superior and lateral structures:

  • stomach ,
  • duodenum ,
  • transverse colon

Pancreas Location

• Epigastrium and left hypochondrium; retroperitoneal
• Anterior to IVC, Aorta, diaphragm.
• Posterior to stomach and transverse colon.
• Level of L1 – L2
• From C- duodenal loop to splenic hilum.
• Across/anterior to aorta
• U-shaped / dumbbell /comma-shaped/ sausage

Pancreas Anatomy Measurements

• Pancreas length 12-18 cm
• Head (larger segment) 2-3 cm AP
• Neck 1.5-2.5 cm AP
• Body 2-3cm AP
• Tail 1-2cm

Function of the Pancreas

• ENDOCRINE (HORMONAL) 10%
  • Islets of Langerhans
    • Alpha (15%-20%): Glucagon
    • Beta: Insulin
    • Delta (5%): Somatostatin
• EXOCRINE (DIGESTIVE) 90%
  • Via ducts
  • Acini cells
  • Pancreatic Juice Components Acts on
    • Amylase Carbohydrates
    • Lipase Fats
    • Trypsin, chymotrypsin, carboxypeptidase Proteins
    • Nucleases Nucleic acids
    • Sodium bicarbonate Hydrochloric acid

Vasculature Around Pancreas

• Portal splenic confluence (merging of superior mesenteric vein and splenic vein) – Posterior to neck of pancreas.
• Gastroduodenal artery (GDA) (branch of the CHA) Inferior and lateral to neck of pancreas.
  • Branches:
    • Anterior and posterior superior pancreaticoduodenal branches. Supply head of pancreas and duodenum.
• The superior mesenteric vein crosses anterior to the uncinate process of the head of the gland and posterior to the neck and body of the pancreas.
• Splenic artery in the superior border of the pancreas. Supplies body and tail.
• Venous drainage is through tributaries of the splenic and superior mesenteric veins.

Vascular and Ductal Landmarks to the Pancreas

• Celiac axis and branches
• Splenic artery
• Common hepatic artery
• Gastroduodenal artery
• Superior mesenteric artery
• Portal vein and tributaries
• Common bile duct

Characteristics of the Normal Pancreas

• Echogenicity: > liver, </> spleen (depends on fatty/fibrous texture)
• Echotexture: Homogeneous
• Surface: Smooth to slightly lobular