The liver is the largest visceral organ in the body. It is predominantly located in the right hypochondrium and epigastric areas and extends into the left hypochondrium. It lies just beneath the diaphragm and is anatomically divided into four lobes (right, left, quadrate, caudate), while functionally and surgically the liver is divided into right and left halves and further subdivided into eight independent hepatic segments, each supplied by a major branch of the hepatic artery, portal vein, hepatic vein, and biliary drainage.

The inferior liver margin is projected on the line that connects the lowest part of the right side of the rib cage, crosses the left side of the rib cage at the level of the cartilage of the 8th rib, and ends on the left side in the 5th intercostal space on the mammillary line (linea mammillaris). The main vessels of the abdominal cavity can be seen through the liver.

The liver has a unique dual blood supply. Hepatic artery supplies the liver with arterial blood. It is derived from the coeliac trunk. Hepatic portal vein supplies the liver with partially deoxygenated blood, carrying nutrients absorbed from the small intestine. Venous drainage of the liver is achieved through hepatic veins. We can differentiate between liver parenchyma, vasculature, gallbladder, and biliary system using the ultrasound. The liver offers an outstanding acoustic window on to other organs and vessels in the upper part of abdomen.

Anatomical location of the liver and surrounding structures.

Available at: http://hepcbc.ca/the-liver/ (Accessed: 19 November 2019).

Healthy liver parenchyma on ultrasound PAME Maribor

Liver venus vasculature

Available at: https://www.med-ed.virginia.edu/courses/rad/gi/liver/anat01.html (Accessed: 19 November 2019).

Ultrasound anatomy of the liver and surrounding structures PAME Maribor

There are various ligaments formed by a double layer of peritoneum. They attach the liver to the surrounding structures. The falciform ligament is the sickle-shaped ligament that connects the anterior surface of the liver to the anterior abdominal wall and forms a natural anatomical division between the left and right lobes of the liver. The free edge of this ligament contains the round ligament of the liver (ligamentum teres), a remnant of the umbilical vein. The coronary ligament (anterior and posterior folds) attaches the superior surface of the liver to the inferior surface of the diaphragm and separates the bare area of the liver. There are two triangular ligaments. The left triangular ligament attaches the left lobe of the liver to the diaphragm. The right triangular ligament attaches the right lobe of the liver to the diaphragm. The lesser omentum attaches the liver to the lesser curvature of the stomach and first part of the duodenum.

There are two liver surfaces: the diaphragmatic and visceral surface. The diaphragmatic surface is anterosuperior, smooth and convex, fitting beneath the curvature of the diaphragm. The visceral surface is posteroinferior and covered with peritoneum, except for the fossa of the gallbladder and porta hepatis. It lies in contact with the right kidney, right adrenal gland, right colic flexure, transverse colon, the first part of the duodenum, gallbladder, esophagus, and the stomach.

Scheme of liver ligaments

Available at: https://images.slideplayer.com/31/9639721/slides/slide_21.jpg (Accessed: 7 March 2020).

Ultrasound image of the gallbladder and ligamentum teres, PAME Maribor

There are four anatomical spaces between the liver and the surrounding structures: two subphrenic spaces, subhepatic space, and Morrison’s pouch. Subphrenic spaces are located between the diaphragm and the anterior and superior aspects of the liver. The falciform ligament divides the left and right subphrenic space. The subhepatic space can be found between the inferior surface of the liver and the transverse colon. The space between the visceral surface of the liver and the right kidney is called Morison’s pouch. It is the deepest part of the peritoneal cavity when lying flat. Therefore, pathological abdominal fluid is most likely to collect in this region.

Liver relations to other organs.

Available at: https://docnesia.com/wp-content/uploads/2018/09/02c29f44a8f060d36e027f2830159e1fde59368c.png (Accessed: 7 March 2020).

Probe position in assessment of hepatorenal recess – Morison's pouch PAME Maribor
Ultrasound image of Morison's pouch PAME Maribor

Available at: https://www.stepwards.com/?page_id=1275 (Accessed: 7 March 2020).

Ultrasound examination

The liver lies primarily in a high subcostal position. Caudal repositioning can be achieved by asking a patient to take a deep abdominal breath. This facilitates access to the ultrasound picture of the liver. A careful subcostal compression of the abdominal wall using the ultrasound transducer also improves image representation characteristics through the displacement of the superimposed intestinal structures as well as optimization of the beam angle and distance to the organ. The liver offers an outstanding acoustic window on to other organs and vessels in the upper part of abdomen.  The liver is a large organ and therefore cannot be scanned adequately from one approach. A complete examination of the liver requires scanning from multiple angles and directions.

A healthy liver ultrasound shows a homogenous, sponge like texture of mid-grey entity, with the same or slightly increased echogenicity as the cortex of the right kidney. A thin, hyperechoic capsule surrounds the smooth parenchyma, which is interrupted by ligaments and vessels. The There are blood vessels that are seen as branching tubular structures that can be traced towards the portal vein or the inferior vena cava.

In the peripheral parts of the liver the hepatic artery branches and biliary ducts are too small to be detected by ultrasound. However the larger, proximal branches can be demonstrated. The three main hepatic veins, left, middle and right, can be traced into the inferior vena cava (IVC) at the superior margin of the liver. The hepatic veins do not have a fibrous sheath and their walls are therefore less reflective than the walls of the portal venous system

The hyperechoic, linear structures on liver ultrasounds are the ligaments. At the superior margin of the liver, there is the falciform ligament, splitting the left and right lobes. The ligamentum teres descends towards the inferoanterior aspect of the liver. The ligamentum venosum separates the caudate lobe from the rest of the liver. The liver is divided into two halfs and aditionally in several segments. The segmental anatomy system is important for surgical procedures, for many pathologies it is however sufficeint to  talk abot the left or right lobes of the liver.

The liver, right kidney, and Morrison’s pouch are assessed using ultrasound in the perihepatic window. A transducer is put in the mid-axillary line at the lever of the 10th rib, with the marker on the probe pointing towards the patient’s head. Ideally, the kidney, liver, and diaphragm are seen at the same time. The hepatorenal recess should be placed in the center of the ultrasound screen. At this point, the probe is tilted around to assess Morrison’s pouch, liver, and kidney. It may be necessary to move one intercostal space inferiorly to evaluate the liver tip. Ribs may get in the way of a clear picture. In this case, the probe can be rotated around its axis, with the marker pointing slightly posteriorly (to get in between the ribs). Another way to avoid rib shadows is to ask the patient to inhale.

There are two signs that we can look for: the mirror effect and spine sign. Because there is air in the lungs, we can see a phenomenon called “the mirror effect.” It occurs where the liver parenchyma is mirrored over the diaphragm. The ultrasound machine assumes the sound moves at the same speed in the body and that it only goes in straight lines. When the sound comes in the interface between something liquid (for example, the liver) and air (for example, the air in the thorax), the interface will create a highly reflective surface for sound. Therefore, the ultrasound machine thinks that something lies on the other side of the diaphragm and produces the mirror effect. So, if the same structure is seen in the abdominal and thoracic cavity, one can assume that there is no fluid in the thorax (just air). The space above the diaphragm is anechogenic in fluidothorax.

We can also look for the so-called “spine sign” (vertebrae and intervertebral discs may be seen in the far-field caudally and to the diaphragm). If the vertebral bodies do not extend past the diaphragm into the thorax, that does not mean that the patient does not have a thoracic spine, it just cannot be seen because of the air in the lungs. On the other hand, if the thoracic spine can be seen, it does not necessarily mean that the patient has fluidothorax (for example, the consolidation of lung tissue in pneumonia can also transmit sound through the lungs and to the spine).

Probe position in assessing the liver, PAME Maribor
Healthy liver parenchyma, PAME Maribor
An example of a mirror effect in a healthy patient. The spine shadow stops at the diaphragm, which excludes fluid in the lungs PAME Maribor
Ultrasound anatomy of the liver and surrounding structures PAME Maribor

Cirrhosis

Cirrhosis is a late stage of scarring (fibrosis) of the liver caused by many forms of liver diseases and conditions. The most common causes of cirrhosis are chronic alcoholism, hepatitis B, hepatitis C, and non-alcoholic fatty liver disease. The liver damage due to cirrhosis generally cannot be undone. However, if liver cirrhosis is diagnosed early and the cause is treated, further damage can be limited and, rarely, reversed.

There are often no symptoms in the early stages of cirrhosis. As the disease worsens, the patient may become:

  • tired and weak,
  • itchy – because of bile salts accumulation,
  • have swelling in the lower legs and build up fluid in the abdomen – circulatory dysfunction,
  • develop yellow skin (jaundice) – due to bilirubin accumulation,
  • bruise easily – the deficit of blood-clotting factors,
  • develop spider-like blood vessels on the skin – the liver cannot metabolize circulating estrogens,
  • caput medusae – portal hypertension and portosystemic shunt.

The diagnostic process starts with a patient’s history. The medical history can reveal excessive and prolonged intake of alcohol, intravenous drug abuse, or a history of hepatitis. On clinical examination, besides previously mentioned clinical signs, we might be able to palpate the lower edge of an enlarged liver below the right rib cage and feel the tip of the enlarged spleen below the left rib cage. A cirrhotic liver might also feel firmer and more irregular than a healthy liver. Esophageal varices may be found unexpectedly during an upper endoscopy because of portal hypertension. These are tiny vessels of the esophagus that become enlarged and may leak when the pressure becomes too high. Advanced cirrhosis leads to a reduced level of albumin in the blood and reduced blood clotting factors due to the loss of the liver’s ability to produce these proteins. An abnormal elevation of liver enzymes in the blood (such as ALT and AST) suggests inflammation or injury of the liver from many causes, including cirrhosis.

The clinical diagnosis of liver cirrhosis is confirmed with the liver biopsy. Patients need regular follow-up examinations every six months to see how the disease progresses. At this stage, clinical examination, blood panel, liver enzymes, kidney function, INR, alpha-fetoprotein, and ultrasound examination can be performed.

Ultrasound examination

The ultrasound examination may show smaller, shrunken liver, however, it may be normal in size, or may undergo disproportionate changes within different lobes.

In cirrhosis the normal architecture of the liver is destroyed due to the formation of bands of fibrous tissue between the hepatic lobules, giving it a nodular appearance. If micronodular, the echotexture is generally coarse, if macronodular, discrete nodules can be distinguished on ultrasound.  Patients with cirrhosis are at increased risk of developing HCC, the detection of which is particularly difficult in an already nodular liver.

In advanced cirrhosis the liver is more highly reflective than the normal liver tissue, which is shown as increased echogenicity. Other liver findings suggestive of cirrhosis in imaging are an enlarged caudate lobe, widening of the fissures, and enlargement of the spleen.

Not necessarily specific to cirrhosis, some haemodynamic changes can be demonstrated on spectral Doppler: reduced velocity, reversed flow, partial or total thrombosis in the portal venous flow and a compensatory increase in hepatic arterial flow.

Normal and cirrhotic liver on the ultrasound picture.

Available at: https://www.startradiology.com/internships/general-surgery/abdomen/ultrasound-abdomen-general/ (Accessed: 7 March 2020).

More examples of cirrhosis, PAME Maribor

More examples of cirrhosis PAME Maribor

Portal vein thrombosis

A portal vein thrombosis is a form of venous thrombosis affecting the hepatic portal vein, which can lead to portal hypertension. It refers to the complete or partial obstruction of blood flow in the portal vein due to the presence of a thrombus in the vessel lumen. It is a relatively common complication in patients with liver cirrhosis.

The portal vein thrombosis is suspected in people who have some combination of the following:

  • bleeding from varicose veins in the esophagus or stomach,
  • an enlarged spleen,
  • conditions that increase the risk of developing portal vein thrombosis (for example, umbilical cord infection in newborns or acute appendicitis in older children).

Besides that, the portal vein thrombosis can cause fever, symptoms of indigestion, and gradually worsening abdominal pain. However, it can also develop without any symptoms, leading to portal hypertension before it is diagnosed. Blood tests determine how well the liver is functioning and whether it is damaged (liver function tests), but results are often normal.

Doppler ultrasonography usually confirms the diagnosis. It shows that blood flow through the portal vein is reduced or absent. In some people, magnetic resonance imaging (MRI) or computed tomography (CT) is necessary.

Angiography is done if a procedure to create an alternate route for blood flow is planned. For angiography, an x-ray of the veins is taken after a radiopaque contrast agent is injected into the portal vein.

Ultrasound examination

Acute thrombosis may be difficult to detect with grey-scale imaging alone, as the thrombus may be hypoechogenic. As time progresses, it becomes more echogenic and easier to identify. A color Doppler test should be able to demonstrate absent flow in the portal vein and even to detect partial thrombosis, but attention to the Doppler gain and filters is necessary to avoid color overwrite of partial thrombosis. The color Doppler is also useful to help evaluate for tumorous thrombus, which will show internal color vascularity. A bland thrombus, in comparison, is avascular on the color Doppler.

Most common locations of portal vein thrombosis

Available at: https://www.researchgate.net/figure/Most-common-sites-of-thrombosis_fig1_279987274 (Accessed: 19 November 2019).

Ultrasound image of portal vein branches and IVC

Available at: http://fasanonet.com/rad/doku.php?id=ultrasound (Accessed: 19 November 2019).

Portal vein thrombosis represented by the presence of echogenic material inside the portal vein, PAME Maribor

Available at: https://prevent-hypertency.blogspot.com/2016/01/signs-of-portal-hypertension-radiology.html (Accessed: 19 November 2019).

Hepatomegaly

Hepatomegaly is the enlargement of the liver and is often a sign that the tissue within the liver is not functioning correctly.

Common causes include:

  • liver or metastatic cancer,
  • non-alcoholic fatty liver disease (NAFLD),
  • heart and blood vessel abnormalities,
  • cirrhosis,
  • infections, such as viral hepatitis (most commonly A, B, or C),
  • alcoholic liver disease, or a range of liver damage that includes fatty deposits, inflammation, and scarring due to alcohol consumption,
  • congestive heart failure can also cause blood to back up into the hepatic veins. These are the veins that help drain blood from the liver. When they back up, the liver will become congested and grow larger (congestive hepatomegaly).

Less common causes of hepatomegaly are lymphoma, leukemia, multiple myeloma, Wilson’s disease, Gaucher’s disease, toxic hepatitis, bile duct obstruction, or hepatic cysts.

The liver is a wedge-shaped organ and is present in the right upper quadrant of the abdomen. The liver typically extends from the fifth intercostal space to the right costal margin in the midclavicular line. The size of the liver increases with age, from an average span of 5 cm at the age of five to 15 cm in adulthood. The size of the healthy liver also varies with sex and body size.

The assessment of liver size is briefly made by the clinical examination. If we want to obtain more precise parameters, ultrasound or CT are the best options.

  1. In a healthy patient, the liver cannot be palpated. The palpation starts in the right lower quadrant of the abdomen. We slowly palpate toward the right costal margin. The whole margin needs to be palpated. Then we put both of our hands under the right costal margin and ask the patient to inhale and exhale. The enlarged liver can slide under our fingers this way. Percussion is another way of determining the size of the liver. The margin of the liver is where the sound of percussion changes.

Ultrasound examination

Ultrasound parameters for the adult liver:

  • Midclavicular line averages 10-12.5 cm in craniocaudal length.
  • The liver that is longer than 15.5-16 cm in the midclavicular line (MCL) is considered enlarged.
  • The average transverse diameter is 20-23 cm at the level of the upper pole of the right kidney.

Features that support hepatomegaly include:

  • extension of the right lobe inferior to the lower pole of the right kidney,
  • rounding of the inferior hepatic border.
Enlarged liver.

Available at: https://www.mayoclinic.org/diseases-conditions/enlarged-liver/symptoms-causes/syc-20372167#dialogId1379504 (Accessed: 3 March 2020)

Palpation of the liver.

Available at: https://www.stepwards.com/?page_id=1275 (Accessed: 7 March 2020).

Abdominal ultrasonography showing hepatomegaly with increased hepatic echogenicity.

Available at: https://www.researchgate.net/figure/Abdominal-ultrasonography-showing-hepatomegaly-with-increased-hepatic-echogenicity_fig3_279518424 (Accessed: 7 March 2020).

Ultrasound liver diameters

Liver lesions

Liver lesions are mostly benign. They do not spread to other areas of the body and usually do not cause any health issues.

Liver cancer usually develops from liver cells called hepatocytes. This type of cancer is referred to as primary liver cancer. Rarely, cancer may develop from cells lining the bile duct or the blood vessels. Other cancers spread to the liver from another area, such as the colon, breast, or lung. These are referred to as metastatic cancers.

There are three main types of liver cancer. These are:

  • Hepatocellular carcinoma (HCC): This is the most prevalent type of liver cancer, accounting for close to 90% of cases. Almost 80% of patients diagnosed with HCC will have underlying cirrhosis.
  • Cholangiocarcinoma (bile duct cancer): This cancer grows in the bile duct of the liver. This narrow tube extends from the liver to the small intestine. It accounts for about 9% of liver cancers.
  • Angiosarcoma: This rare kind of liver cancer accounts for only about 1% of cases. It is an aggressive, rapidly growing cancer that starts in the blood vessels of the liver.

Ultrasound examination

The effect of a focal mass on surrounding structures is called the “mass effect”. It describes the displacing or invasive nature of the lesion, shown, for example, as the displacement of vessels and/or invasion or distortion of adjacent structures and tissues.The mass effect can help us differentiate a true mass from an infiltrative process, or an artefact. However, it does not distinguish between benign and malignant masses. Sometimes, it can be the main sign of a mass, when the mass is isoechoic compared to normal liver tissue.

Metastases

Many malignant tumours metastasize to the liver, but it is not possible to characterise the primary source of the metastases, solely by their ultrasound features. On ultrasound the metastases tend to be solid and have ill-defined margins. In comparation with normal immediate liver parenchyma, they may be hyperechoic, hypoechoic, isoechoic or of mixed pattern. The larger ones may contain fluid due to central necrosis. Calcification within a deposid can show distal acoustic shadowing. A lobulated outline to the liver, hepatomegaly and ascites can also present in association with metastases on the ultrasound examination .

Hepatocellular carcinoma (HCC)

On the ultrasound HCC may appear as hypo or  hyperechogenic or as a lesion with mixed echogenicity. Observed lesions may be solitary or multifocal. Often HCC is hard to locate in cirrhotic liver within an already coarse and nodular texture.

To supply the growing lesion, all carcinomas demonstrate neovascularization. Doppler modalities therefore demonstrate vigorous flow, helping to distinguish HCCs from metastases or haemangiomas, which demonstrate little or no flow.

Haemangioma

These common, benign lesions are highly vascular, composed of a network of tiny blood vessels. They may be solitary or multiple. Most haemangiomas are small (usually less than 2 cm) and found incidentally. They are rarely symptomatic. Their ultrasound appearances vary. The majority are hyperechoic, rounded well-defined lesions. However, atypical hypoechoic lesions or those with mixed echogenicity cause diagnostic dilemmas. Because the blood within the haemangioma is very slow flowing, it is usually not possible to demonstrate flow with colour or power Doppler and the lesions appear avascular on ultrasound.

An example of hepatic haemangioma

Available at: https://en.wikipedia.org/wiki/Cavernous_liver_hemangioma (Accessed: 19 November 2019).

Liver cysts

Liver cysts are abnormal sacs in the liver that may contain fluid or a solid mass of cells. They usually do not cause any symptoms. However, they may become large enough to cause pain or discomfort in the upper right part of the abdomen. Most liver cysts can be detected on ultrasound or computerized tomography (CT) scans. When needed, treatment may include drainage or removal of the cyst.

Simple hepatic cysts may be isolated, or there can be multiple cysts. They may vary from a few millimeters to several centimeters in diameter. On histopathological analysis, true hepatic cysts contain serous fluid and are lined by a nearly invisible wall consisting of cuboidal epithelium, identical to that of bile ducts, and a thin underlying rim of fibrous stroma.

Ultrasound examination

One of the most frequently seen liver lesions, the simple cyst, is either congenital  or acquired. It is asymptomatic, unless large enough to cause a ‘mass effect’, compressing and displacing adjacent structures, and is usually an incidental finding during the ultrasound scan. Frequently, small cysts are peripheral and therefore more likely to be missed on ultrasound than CT.

Ultrasound properties of the simple liver cyst;

  • anechoic
  • has a well-defined smooth capsule
  • exhibits posterior enhancement (increased throughtransmission of sound)
  • no internal vascularity on the color Doppler
Examples of liver cysts, PAME Maribor

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