Liver Anatomy and Ultrasound – Vocabulary Flashcards
Anatomy and physiology of the liver
Purpose: comprehensive study notes derived from the provided transcript covering anatomy, vessels, ligaments, Couinaud’s segmentation, sonographic evaluation, and clinical relevance.
Location and relationships
Location: occupies the right hypochondrium, most of the epigastrium, and extends into the left hypochondrium up to the mammillary line.
Relationship to surrounding organs:
Fundus of stomach lies posterior and lateral to the left lobe.
Rest of the stomach lies inferior to the liver.
Body of the pancreas lies inferior to the left lobe.
Diaphragm: liver lies inferior to the diaphragm.
Lobes of the liver
Principal lobes (anatomical): Right lobe, Left lobe, Caudate lobe.
Additional anatomical features include a split within the right lobe into anterior and posterior segments.
Commonly taught as lobes: Right, Left, Caudate.
Surface anatomy and fissures
Bare area: portion of the liver not covered by peritoneum; rests on the diaphragm and is contiguous with Glisson capsule.
Glisson capsule: peritoneal covering around most of the liver.
Fissures and ligaments define liver partitioning:
Main lobar fissure: separates right and left lobes; identifiable between gallbladder neck and portal vein junction.
Right intersegmental fissure: divides right lobe into anterior and posterior segments; landmark: right hepatic vein.
Left intersegmental fissure: divides left lobe into medial and lateral segments; landmarks: left hepatic vein, left portal vein, falciform ligament, ligamentum teres.
Ligamentum venosum: separates caudate lobe from the left lobe; remnant of the ductus venosus; landmark: left lobe and IVC.
Falciform ligament: connects liver to anterior abdominal wall (umbilicus to diaphragm) and contains the ligamentum teres; adheres liver to anterior abdominal wall.
Coronary and triangular ligaments: connect liver to the diaphragm; provide diaphragmatic (superior) attachments.
Ligaments and fissures together help define the hepatic anatomy visible on imaging.
Ligaments and remnants of fetal circulation
Ligamentum teres (round ligament): remnant of the umbilical vein that ran from the umbilicus to the left portal vein in the fetus; becomes part of the falciform ligament; can recanalize in portal hypertension.
Ligamentum venosum: remnant of the ductus venosus; intrahepatic course; separates caudate from left lobe; connects left portal vein to IVC.
Coronary and triangular ligaments anchor the liver to the diaphragm.
Vascular supply and drainage
Portal system (major inflow):
Portal vein carries about 70$-$80 ext{%} of liver inflow, from the intestines via the portal venous system.
Hepatic artery provides about 30 ext{%} of inflow, originating from the celiac trunk/axis as the common hepatic artery and its branches.
Portal vein formed by splenic vein and superior mesenteric vein (SMV).
MPV enters the liver and divides into left and right branches.
Hepatopetal flow: toward the liver.
Diameter near porta hepatis: typically around 13 ext{ mm}; larger diameter can suggest portal hypertension.
Portal venous branches: right side portal vein is usually short and gives rise to right anterior (segments V and VIII) and right posterior (segments VI and VII) branches; left portal vein supplies left lobe segments II–IV and IV-related segments.
Intrasegmental vs intersegmental vessels:
Intrasegmental: portal veins coursing through the center of each Couinaud segment; encased by Glisson’s capsule with echogenic walls.
Intersegmental hepatic veins: course between segments and lobes; have thinner, less echogenic walls than portal veins.
Hepatic veins (outflow): drain blood from liver to IVC; three main trunks: right hepatic vein (RHV), middle hepatic vein (MHV), left hepatic vein (LHV).
Blood flows from liver toward the right atrium.
The hepatic veins separate the liver both vertically (into four parts) and longitudinally between lobes/segments.
Biliary system (in relation to portal triad): common bile duct (CBD) courses with portal triad in the portal triad region and drains bile from the gallbladder and liver into the duodenum.
Couinaud’s liver segments (8 functional segments)
Segment I: Caudate lobe
Segment II: Left lateral superior
Segment III: Left lateral inferior
Segment IVa: Left medial superior (part of medial left; quadrate region)
Segment IVb: Left medial inferior (quadrate region)
Segment V: Right anterior inferior
Segment VI: Right posterior inferior
Segment VII: Right posterior superior
Segment VIII: Right anterior superior
Key concept: segments are defined by their vascular inflow (portal veins) and outflow (hepatic veins); functional units that can be resected independently (Couinaud system).
Mnemonics and landmarks used in imaging: use markers and landmarks like RHV, MHV, LHV, LPV, MPV, gallbladder fossa, ligamentum teres, ligamentum venosum to delineate segments.
Segment-related landmarks and practical notes
Right lobe segmentation:
Anterior segment: segments V and VIII
Posterior segment: segments VI and VII
Left lobe segmentation:
Medial segments: IVa and IVb (quadrate lobe region)
Lateral segments: II and III
Caudate lobe (Segment I) landmarks: located posteriorly; border between left lobe and caudate separated by ligamentum venosum; venous drainage via emissary veins into IVC; often spared from disease due to drainage patterns.
Imaging landmarks and portal triad appearance
Portal triad in imaging appears as an echogenic bundle within a Glisson’s capsule: portal vein, hepatic artery, and common bile duct.
The portal triad is encased in a collagenous sheath; CBD often runs posterior to the hepatic artery and anterior to the portal vein in the portal triad view.
Hepatic artery walls are typically less echogenic than the portal vein walls; portal veins have bright echogenic walls due to collagen.
Normal anatomic variations and notable anomalies
Common variants and anomalies include:
Riedel’s lobe: inferior projection of the right lobe; more common in women.
Variations in left lobe size and impressions: very small left lobe; deep costal impressions; complete atrophy of the left lobe can compress the left portal vein; saddle-shaped liver; tongue-like left lobe; deep renal impressions; diaphragmatic grooves; corset constriction.
Agenesis: agenesis of any lobe is incompatible with life; reported cases with absence of a right, left, or caudate lobe lead to hypertrophy of remaining lobes.
Situs inversus: liver on left with spleen on right; may also occur with diaphragmatic hernia or omphalocele where liver tissue herniates.
Accessory fissures: true accessory fissures are uncommon and due to infolding of peritoneum (e.g., inferior accessory fissure from right portal vein to inferior surface of right lobe).
Vascular anomalies: hepatic arteries variations are common (≈45%): replaced left hepatic artery from left gastric artery; replaced right hepatic artery from superior mesenteric artery; replaced common hepatic artery from SMA.
Portal vein variations: less common but can include atresias, strictures, obstructing valves; accessory hepatic veins draining unusual segments into middle or right hepatic veins.
Functional emphasis: Liver functions and clinical testing
Primary functions:
Detoxifies blood; processes nutrients; metabolizes foodstuff into usable forms.
Produces bile to aid digestion of fats; essential for fat emulsification.
Destroys old red blood cells; produces bilirubin (pigment from heme breakdown).
Synthesizes plasma proteins (e.g., albumin) and produces enzymes (AST, ALT, alkaline phosphatase).
Regulates blood composition and produces cholesterol and various metabolites.
Liver function tests (LFTs):
AST (aspartate aminotransferase): elevated in acute hepatitis and cirrhosis.
ALT (alanine aminotransferase): more specific for liver injury.
LDH (lactic dehydrogenase): found in multiple tissues.
Alkaline phosphatase (ALP): elevated in intrahepatic and extrahepatic obstruction and carcinoma.
Bilirubin (indirect/direct/total): reflects bilirubin handling.
Prothrombin time (PT): indicator of liver synthetic function and clotting.
Albumin and globulins: synthesis by liver; used to assess hepatic synthetic capacity.
Interpretation patterns:
Obstructive disease: mild AST/ALT increase with a marked rise in ALP and bilirubin; often due to ductal compression or obstruction.
Hepatocellular disease: marked AST/ALT elevation with a lesser ALP rise; reflects cellular injury.
Sonographic evaluation of the liver
Patient preparation: NPO for at least 6–8 hours (morning exam preferred).
Transducer: 2.5–4 MHz curvilinear/sector or 3–5 MHz curvilinear.
Patient position: supine, with oblique or decubitus as needed to optimize visualization.
History and lab data collection:
Review order and prior imaging; check LFTs (alk phos, AST, ALT, bilirubin, albumin).
Document symptoms and prior interventions; assess last oral intake.
Sonographic technique and optimization:
Adjust time gain compensation (TGC) to equalize echoes across liver; adjust overall gain for detail; adjust depth and focal zones.
Evaluate liver size in longitudinal plane: superior–inferior dimension roughly ext{about }15 ext{ cm}; measure anterior–posterior dimension for compression and contour.
Assess parenchymal texture: should be homogeneous and smooth.
Echogenicity: typically greater than right kidney and less than pancreas; evaluate for hepatosteatosis or fibrosis.
Visualize hepatic vascular structures, ligaments, and fissures for anatomic landmarks.
Morison’s pouch and right subhepatic space should be evaluated for fluid.
Subphrenic space adjacent to the diaphragm evaluated for abscess.
Normal anatomy expectations:
Normal liver to kidney relationship; liver is generally homogeneous with mild echogenicity; venous anatomy identifiable with color Doppler.
Hepatic veins: non-echogenic walls relative to portal veins; draining toward the IVC.
Measurements for hepatomegaly:
Hepatomegaly is indicated when the superior–inferior dimension exceeds 15.5 ext{ cm} on longitudinal view.
Doppler considerations (educational):
Portal venous flow is hepatopetal (toward liver); hepatic venous flow is hepatofugal (toward IVC/heart).
Portal vein diameter and flow patterns can help assess portal hypertension.
The instructor notes that Doppler proficiency for liver is not required for the class, but portal hypertension concepts may be covered later.
Functional and practical implications
Clinical relevance of anatomy:
Knowledge of Couinaud segments guides surgical planning and targeted biopsy or lesion resection.
Understanding fissures and ligaments helps interpret imaging and potential sites of variant anatomy.
Recognition of vascular anatomy variations is crucial during planned interventions (embolization, transplant planning, etc.).
Imaging correlations:
Ultrasound appearance is influenced by fatty change, cirrhosis, and edema; the echogenicity should be interpreted relative to the kidney and pancreas.
Abnormal contour, surface nodularity, or focal lesions require further imaging (CT/MRI) or biopsy as per clinical context.
Quick recap: key measurements and concepts
Normal liver size: approximate superior–inferior length around 15 ext{ cm}; width less than about 14 ext{ cm} in some views.
Portal system:
Portal vein: inflow from SMV and splenic vein; hepatopetal flow; diameter ~13 ext{ mm} at porta hepatis; branches into left and right lobes; right side gives rise to anterior/posterior branches supplying segments V–VIII; left supplies II–IV.
Blood supply ratio: portal venous input ~70$-$80 ext{%}; hepatic arterial input ~30 ext{%}.
Venous drainage: hepatic veins (RHV, MHV, LHV) to IVC; liver outflow follows these veins.
Couinaud segments: I–VIII with the mapping described above; segmentation based on portal inflow and venous drainage.
Ligaments and fissures: Falciform, Ligamentum teres, Ligamentum venosum; Coronary and triangular ligaments; Main lobar fissure; Right/Left intersegmental fissures.
Common pathologies and variations: agenesis, situs inversus, diaphragmatic hernia/omphalocele, accessory fissures, and arterial/venous variations.
Ethical, philosophical, and practical implications
Understanding anatomical variability emphasizes personalized planning in surgery and interventional radiology; standard teaching assumes typical anatomy but real patients may present variants.
Noninvasive imaging (ultrasound) remains a cornerstone for initial assessment, reducing risk and guiding further testing when anomalies are suspected.
The liver’s central metabolic role underlines how systemic disease (cardiovascular, biliary, infectious, or inflammatory processes) can impact hepatic structure and function.
References and study aids
Couinaud’s segmentation (8 segments) as the foundational framework for liver localization and surgical planning.
Landmarks to identify segments on imaging: RHV, MHV, LHV; LPV and its divisions; MPV and its branches; GB fossa; ligamentum teres; ligamentum venosum.
Mnemonics and hands-on practice: use a “Couinaud’s fist” approach to visualize segment boundaries in 3D during study sessions.