Diagnostic Ultrasound - Abdomen and Pelvis

Liver
4
Anatomy: Abdomen
GROSS ANATOMY
Overview
• Liver is largest gland and largest internal organ (average
weight: 1,500 grams)
○ Functions
– Processes all nutrients (except fats) absorbed from GI
tract; conveyed via portal vein
– Stores glycogen, secretes bile
○ Relations
– Anterior and superior surfaces are smooth and convex
– Posterior and inferior surfaces are indented by colon,
stomach, right kidney, duodenum, inferior vena cava
(IVC), gallbladder
○ Covered by peritoneum except along gallbladder fossa,
porta hepatis, and bare area
– Bare area: Nonperitoneal posterior superior surface
where liver abuts diaphragm
– Porta hepatis: Portal vein, hepatic artery, and bile duct
are located within hepatoduodenal ligament
○ Falciform ligament: Extends from liver to anterior
abdominal wall
– Separates right and left subphrenic peritoneal
recesses (between liver and diaphragm)
– Marks plane separating medial and lateral segments
of left hepatic lobe
– Carries round ligament (ligamentum teres), fibrous
remnant of umbilical vein
○ Ligamentum venosum: Remnant of ductus venosus
– Separates caudate from left hepatic lobe
• Vascular anatomy (unique dual afferent blood supply)
○ Portal vein
– Carries nutrients from gut and hepatotrophic
hormones from pancreas to liver along with oxygen
(contains 40% more oxygen than systemic venous
blood)
– 75-80% of blood supply to liver
○ Hepatic artery
– Supplies 20-25% of blood
– Liver is less dependent than biliary tree on hepatic
arterial blood supply
– Usually arises from celiac artery
– Variations are common, including arteries arising from
superior mesenteric artery
○ Hepatic veins
– Usually 3 (right, middle, and left)
– Many variations and accessory veins
– Collect blood from liver and return it to IVC at
confluence of hepatic veins just below diaphragm and
entrance of IVC into right atrium
○ Portal triad
– At all levels of size and subdivision, branches of
hepatic artery, portal vein, and bile ducts travel
together
– Blood flows into hepatic sinusoids from interlobular
branches of hepatic artery and portal vein →
hepatocytes (detoxify blood and produce bile) → bile
collects into ducts, blood collects into central veins →
hepatic veins
• Segmental anatomy of liver
○ 8 hepatic segments
– Each receives secondary or tertiary branch of hepatic
artery and portal vein
– Each is drained by its own bile duct (intrahepatic) and
hepatic vein branch
○ Caudate lobe = segment 1
– Has independent portal triads and hepatic venous
drainage to IVC
○ Left lobe
– Lateral superior = segment 2
– Lateral inferior = segment 3
– Medial superior = segment 4A
– Medial inferior = segment 4B
○ Right lobe
– Anterior inferior = segment 5
– Posterior inferior = segment 6
– Posterior superior = segment 7
– Anterior superior = segment 8
IMAGING ANATOMY
Internal Contents
• Capsule
○ Reflective Glissoncapsule making borders of liver well
defined
• Left lobe
○ Contains segments 2, 3, 4A, and 4B
○ Longitudinal scan
– Triangular in shape
– Rounded upper surface
– Sharp inferior border
○ Transverse scan
– Wedge-shaped tapering to left
○ Liver parenchyma echoes are mid gray with uniform
sponge-like pattern interrupted by vessels
• Right lobe
○ Contains segments 5, 6, 7, and 8
○ Liver parenchymal echoes similar to left lobe
○ Sections of right lobe show same basic shape, though
right lobe is usually larger than left
• Caudate lobe
○ Longitudinal scan
– Almond-shaped structure posterior to left lobe
○ Transverse scan
– Seen as extension of right lobe
• Portal veins
○ Have thicker reflective walls than hepatic veins; portal
veins have fibromuscular walls
○ Wall reflectivity also depends on angle of interrogation;
portal veins cut at more oblique angle may have less
apparent wall
○ Can be traced back towards porta hepatis
○ Normal portal flow is hepatopetal on color Doppler;
absent or reversal of flow may be seen in portal
hypertension
○ Normal velocity 13-55 cm/s
○ Portal waveform has undulating appearance due to
variations with cardiac activity and respiration
○ Branches run in transverse plane
○ Hepatic portal vein anatomy is variable
• Hepatic veins