The liver is an intraperitoneal organ located primarily in the right hypochondrium, epigastric, and part of the left hypochondrium regions.
It is the largest organ in the abdomen, the second largest in the body, and the largest gland with both exocrine and endocrine functions.
The liver typically measures 13-15 cm in length and weighs between 1400-1600 grams.
Liver Coverings
The liver is covered by the peritoneum, except for the bare area, which attaches directly to the diaphragm.
Glisson’s capsule, a connective tissue layer, surrounds the liver and the portal triad. It is highly reflective on ultrasound.
Liver Composition and Structure
The liver is composed of hepatocytes, bile duct cells, and vascular cells.
Functional units are called lobules, which are hexagonal in shape.
Hepatocytes are arranged in columns called cords, separated by vascular sinusoids.
Portal triads are located at the vertices of each lobule, receiving blood from the hepatic artery and portal vein.
Blood flows into sinusoids and drains into a central vein, which unites to form hepatic veins that drain into the inferior vena cava (IVC).
Kupffer cells line the lobules and cleanse the blood.
Liver Lobes and Segments
Right Lobe: The largest lobe, located in the right hypochondrium, bordered by the falciform ligament.
The falciform ligament conducts the umbilical vein in the fetus; postnatally, it atrophies into the ligamentum teres.
Inferior and posterior surfaces are marked by the porta hepatis, gallbladder, and IVC.
Divided into right anterior and posterior segments by the right hepatic vein.
Left Lobe: Located in the epigastric and left hypochondriac regions, separated from the right lobe by the middle hepatic vein and the main lobar fissure.
Divided into left lateral and medial segments by the left hepatic vein and the ligamentum teres.
The ligamentum teres appears as an echogenic structure on transverse images and can have varying shapes, sometimes casting an acoustic shadow.
Caudate Lobe: The smallest lobe, located on the posterior-superior surface of the right lobe.
Bounded inferiorly by the main portal vein, posteriorly by the IVC, and anteriorly by the ligamentum venosum (the atrophied ductus venosus).
Couinaud Classification System
Divides the liver into eight functional segments based on the portal vein bifurcation (horizontally) and hepatic veins (vertically).
Each segment has its own vascular inflow (portal vein and hepatic artery) and bile outflow.
The caudate lobe is segment one; the other segments are numbered counterclockwise.
Hepatic veins run intersegmentally, while portal veins run intrasegmentally, except for the ascending portion of the left portal vein.
Knowledge of this classification is crucial for interpreting CT and MRI reports.
Segments 6 and 7 belong to the anterior segment.
Segments 5 and 8 belong to the posterior segment.
Segment 4 is the quadrate lobe.
Segments 2 and 3 are the Lateral segment.
Liver Ligaments and Fissures
Ligaments attach the liver to the diaphragm, stomach, anterior abdominal wall, and retroperitoneum. They appear hyperechoic due to fat and collagen content.
Falciform Ligament: Extends from the umbilicus to the diaphragm, running along the liver’s anterior surface, continuous with the ligamentum teres.
Ligamentum Teres: The rounded termination of the falciform ligament, the obliterated fetal umbilical vein, divides the medial and lateral lobes of the left lobe.
Ligamentum Venosum: The obliterated fetal ductus venosus separates the caudate lobe from the left lobe.
Main Lobar Fissure: Separates the right lobe from the left lobe, runs from the right portal vein to the gallbladder fossa.
The middle hepatic vein courses within it.
Right Intersegmental Fissure: Contains the right hepatic vein, dividing the right lobe into anterior and posterior segments.
Left Intersegmental Fissure: Contains the left hepatic vein, the ligamentum teres, and the ascending portion of the left portal vein, dividing the left lobe into medial and lateral segments.
Liver Circulation
Dual blood supply: hepatic artery (20-30% oxygenated blood) and portal vein (70-80% nutrients, contaminants, and partially oxygenated blood).
Vessels enter the liver at the porta hepatis.
Blood mixes in the sinusoids, hepatocytes extract oxygen and nutrients, eliminate waste, store vitamins and minerals, and produce bile.
Blood drains into the central hepatic vein of the lobule.
The portal vein is formed by the confluence of the splenic and superior mesenteric veins, posterior to the neck of the pancreas.
Portal circulation is separate from the systemic circulation.
The main portal vein divides into the right and left portal veins at the porta hepatis.
The right portal vein divides into anterior and posterior branches.
The left portal vein travels anteriorly, proximal to the falciform ligament and caudate lobe.
The common hepatic artery, a branch of the celiac axis, courses anterior to the portal vein and medially to the common bile duct.
After giving off the gastroduodenal artery (GDA) branch, it becomes the proper hepatic artery.
The proper hepatic artery divides into the right and left hepatic arteries at the porta hepatis.
Common anatomic variants include replaced left hepatic artery (from the left gastric artery) and replaced right hepatic artery (from the superior mesenteric artery - SMA).
If the hepatic artery is replaced it will be seen coursing between the portal vein and the IVC.
Hepatic veins (right, middle, and left) drain into the IVC.
The right hepatic vein drains the anterior and posterior segments of the right lobe.
The middle hepatic vein drains the right anterior and the left medial lobes.
The left hepatic vein drains the medial and lateral segments of the left lobe.
The middle and left hepatic veins often form a common trunk.
An inferior right hepatic vein may drain directly into the IVC.
The caudate lobe drains directly into the IVC via caudate veins.
Portal Triad Anatomy
Consists of a branch of the portal vein, a branch of the hepatic artery, and a bile duct within Glisson’s capsule.
Hepatic ducts transport bile to the gallbladder for storage.
The porta hepatis is located medially in the hilum.
The hepatic artery and common bile duct course anterior to the portal vein, with the common bile duct coursing laterally to the hepatic artery.
Lymph nodes in the porta hepatis may cause biliary obstruction if enlarged.
Liver Physiology
Major functions include excretory, metabolic, storage, and synthetic.
Specific functions: producing bile; metabolizing fats, carbohydrates, and proteins; storing carbohydrates, vitamins, and lipids; synthesizing major proteins; detoxifying ammonia and other harmful chemicals; assisting in lymph fluid formation; and regulating blood volume and body heat.
Sonographic Appearance
Normal liver texture is a homogeneous gray scale, with echo brightness slightly greater than normal renal cortex and slightly less than normal pancreatic tissue.
Echogenicity of soft tissue in the abdomen: renalsinus>pancreas>spleen>liver>renalcortex
Hepatic and portal vessels are distinguished by:
Hepatic veins are larger in diameter at the diaphragm, while portal veins are larger near the porta hepatis.
Hepatic vein branches point to the diaphragm, and portal vein branches point to the porta hepatis.
Hepatic veins usually appear borderless, while portal vein walls are echogenic.
Hepatic veins display a multicomponent waveform, and portal veins exhibit continuous flow.
Echogenic walls near the IVC are caused by specular reflections.
Anatomic Variations
Reidel’s Lobe: An inferior extension of normal liver tissue of the right lobe, more common in women, may present as hepatomegaly. Only the length of the liver will be increased.
Liver Pathologies
Metastatic disease is more common than primary cancer. The gastrointestinal tract is the most common primary site; other sources include the kidneys and ovaries.
Sonographers should sweep the pancreas, large intestine, kidneys, and female pelvis in search of a primary cancer.
Ultrasound of the Liver: Patient Prep
Patients should be fasting (NPO) for 6-8 hours to reduce bowel gas and allow gallbladder dilatation.
NPO is preferred even if the biliary system isn't being evaluated.
Ultrasound of the Liver: Transducer
A 3–3.5 MHz curved linear array transducer is generally prefered.
Lower frequencies are needed for obese patients with fatty livers or cirrhotic livers.
Higher frequencies can be used in thin or pediatric patients, or to evaluate the capsular nodularity in cirrhotic patients.
Ultrasound of the Liver: Breathing Technique
Scanning is performed using a subcostal approach with the patient holding his or her breath in a deep inspiration or with intercostal views with the patient in suspended or quiet respiration.
Ultrasound of the Liver: Patient Position
Patients are scanned in a supine position initially and placed in other positions as needed.
Ultrasound of the Liver: Scanning Technique
Combination of subcostal and intercostal views.
Systematic scans in longitudinal and transverse planes, with oblique and decubitus views as needed.
Ultrasound of the Liver: Technical Tips
To see the dome of the liver, angle the transducer upward, parallel to the ribs.
Ultrasound of the Liver: Required Images
Longitudinal and Sagittal Images
Longitudinal image of the left lobe to include its inferior margin and the abdominal aorta. Suggested annotation: ML
Longitudinal images of the left lobe at 2 to 3 cm intervals until you are completely through the left lobe. The number of images taken will depend on the size of the left lobe. Suggested annotation: SAG LT
Longitudinal image of the caudate lobe. Head of Pancreas Caudate Lobe. Suggested annotation: SAG CAUDATE
Longitudinal image of the right lobe just lateral to the IVC. Suggested annotation: SAG RT
Longitudinal images of the right lobe at 2–3 cm intervals from the right hepatic vein to past the right kidney. Suggested annotation: SAG RT
Longitudinal image of the right lobe to include the right kidney for parenchyma comparison. Suggested annotation: LIVER / RT KIDNEY or RT KID
Longitudinal image of the dome and the adjacent pleural space. Suggested annotation: SAG RT DOME
Longitudinal image of the right lobe measuring the longest length. The liver is best measured at mid–right clavicle (left image). If this is not possible, move the transducer to the edge of the body near the curve of the rib and angle medially until you determine the longest length (right image). Note that the two measurements are very close. RT MID CLAV 14.13cm 170dB/C 3 Persist Off 2D Opt:FSCT Fr Rate:Surv SonoCT® 170dB/C 3 Persist Off 2D Opt:FSCT Fr Rate:Surv SonoCT® 14.50cm Suggested annotation: LIVER or LIVER LENGTH
Transverse Images
Transverse image of the left lobe to include its lateral margin. Suggested annotation: TRV LT
Transverse images of the left lobe to include the ligamentum teres (left image) or ascending branch of the left portal vein (right image). Suggested annotation: TRV LT
Transverse image to include the hepatic veins. Suggested annotation: TRV HVS
Transverse images of the right lobe just past the hepatic veins. Right image demonstrates a mirror image artifact across the diaphragm. Suggested annotation: TRV RT
Transverse image of the right lobe to include (A) the main portal vein, (B) at the level of the right portal vein, and (C) color Doppler image of the main portal vein showing flow direction. Notice the 2 small liver cysts in A. A B Suggested annotation: TRV RT
Transverse images of the right lobe at 2–3 cm intervals until the upper pole of the right kidney is seen. Suggested annotation: TRV RT
Transverse image of the right lobe to include mid–right kidney. Suggested annotation: TRV RT
Transverse image of the right lateral lobe at 2-3 cm interval until out of liver. Suggested annotation: TRV RT
Transverse image of the right lateral lobe to include the gallbladder if visualized. Suggested annotation: TRV RT or TRV GB
Transverse image of the right lateral lobe to include the dome and the adjacent pleural space. Heart Suggested annotation: TRV DOME
The following protocol is for evaluating only the liver.
Reasons to scan just the liver include looking for a mass; clarifying an area seen on CT or MRI; evaluating polycystic disease, abscess, or hematoma; or following a mass after treatment.
Some laboratories may routinely perform a right upper quadrant examination (see Chapter 11 for that protocol).
Elastography of the Liver
Chronic liver disease can lead to liver fibrosis and liver failure, often resulting from viral hepatitis B, alcoholic liver disease, chronic hepatitis C, nonalcoholic fatty liver disease (NAFLD), and Non-Alcoholic SteatoHepatits (NASH).
Elastography stages the degree of fibrosis.
It is important to evaluate for the progression or regression of fibrosis if being treated, which is important to the clinician.
Liver biopsy was previously required to stage fibrosis.
Shear Wave Elastography (SWE)
Uses acoustic radiation force impulse (ARFI).
A push pulse compresses tissue, producing shear waves perpendicular to the push pulse.
Detection pulses measure the speed of shear waves.
The stiffer the tissue, the faster the shear wave velocity.
Results are displayed in meters per second (m/s) or megapascals (MPa).
Each manufacturer has its own chart to determine fibrosis based on shear wave speed.
The ARFI pulse is quickly attenuated and is good only up to 6 to 8 cm.
Performing a Liver Elastography Examination
Based on the Society of Radiologists in Ultrasound (SRU) Liver Elastography Consensus Panel from 2014.
Patient Prep
NPO for 4-6 hours.
Eating increases blood flow to the liver, increasing stiffness and overestimating disease.
Patient Position
Supine or slight 30-degree left posterior oblique position with the right arm raised.
An intercostal approach is used.
Transducer Position
Intercostal position, free of reverberations.
Region of interest (ROI) placement:
Place the box at the liver 2 cm below Glisson’s capsule, perpendicular to the capsule. The box should be placed at segment 7 or 8 of the right lobe.
Do not include blood vessels, rib shadow, the diaphragm, the liver/kidney interface, the liver capsule, or any ligaments because this will cause inaccurate measurements.
Breathing Technique
Neutral breath hold because deep inspiration or expiration will affect the measurement.
The patient should pause breathing in a neutral, relaxed state for only 1 to 2 seconds.
Measurements
Take 10 measurements from the same location, to accurately sample the tissue.
Allow the transducer to cool down between samples.
Delete errors in measurement. For example, the patient took a deep breath or the machine gave an error value.
Use the median value, not the mean or average value.
Report the interquartile ratio (IQR), which should be less than 0.30.
If IQR is greater than 0.30, evaluate numbers and delete outliers. New measurements should be obtained using the same area until there is a total of 10 good measurements.
Procedure Time
Usually a dedicated examination taking 10-15 minutes.