chapter 10

THE LIVER

Diffuse Pathologies - Chapter-10

Pathologic Anomalies of the Liver

  • Developmental Anomalies:

    • Agenesis of the liver is incompatible with life.

    • Agenesis can affect:

      • Right lobe

      • Left lobe

      • Caudate lobe

    • When agenesis occurs, hypertrophy of the remaining lobes develops.

  • Anomalies of Position:

    • The liver may be found in unusual positions under two conditions:

    • Situs Inversus:

      • Organs are mirrored in position relative to their normal placement (e.g., the liver is on the left, and the spleen is on the right).

    • Congenital Diaphragmatic Hernia or Omphalocele:

      • In these conditions, some liver tissue may herniate into the thorax or outside the abdominal cavity.

  • Accessory Fissures:

    • The inferior accessory hepatic fissure stretches inferiorly from the right portal vein to the inferior surface of the right lobe of the liver.

Hepatic Artery Variations

  • The hepatic artery can show multiple variations as it arises from the celiac axis:

    • At least 45% of individuals may experience variations, such as:

    1. Replaced Left Hepatic Artery:

      • Originating from the left gastric artery.

    2. Replaced Right Hepatic Artery:

      • Originating from the superior mesenteric artery.

    3. Replaced Common Hepatic Artery:

      • Arising from the superior mesenteric artery.

Diffuse Disease: Fatty Infiltration

  • Diffuse Hepatocellular Disease:

    • This condition impacts the hepatocytes and disrupts liver function.

    • Fatty Liver:

    • An acquired, reversible metabolic disorder characterized by the accumulation of triglycerides in the hepatocytes.

Causes of Fatty Liver

  • Primary Causes Include:

    • Obesity

    • Excessive alcohol intake

    • Poorly controlled hyperlipidemia

    • Diabetes

    • Excess corticosteroids

    • Conditions during pregnancy

    • Total parenteral hyperalimentation

    • Severe hepatitis

    • Glycogen storage diseases

    • Cystic fibrosis

    • Pharmacological effects

  • Signs and Symptoms:

    • Generally asymptomatic

    • Rarely causes abnormal liver function tests (LFTs).

Diffuse Disease: Fatty Infiltration (Imaging Details)

  • Ultrasound Findings:

    • Fatty infiltration shows a diffuse distribution and results in increased echogenicity of the liver.

    • Comparison:

    • Comparing liver parenchyma to kidney enhances the diagnosis.

    • Pathology Images:

    • A: Gross pathology of diffuse fatty liver parenchyma.

    • B: Comparison of normal liver (left) versus fatty liver (right).

Types of Fatty Infiltration (Ultrasound Grades)

  • Grade I (Mild):

    • Ultrasound shows minimal diffuse increase in hepatic echogenicity with normal visualization of the diaphragm and intrahepatic vascular borders.

  • Grade II (Moderate):

    • Increased echogenicity with slightly impaired visualization of the diaphragm and intrahepatic vascular borders.

  • Grade III (Severe):

    • Significant increase in echogenicity with decreased or poor visualization of the diaphragm and hepatic vessels.

Focal Fatty Infiltration and Focal Fatty Sparing

  • Focal Fatty Sparing:

    • Defined as a hypoechoic focal area of normal liver tissue within a fatty infiltrated liver, commonly found in diabetics.

  • Focal Fatty Infiltration:

    • Represents regions of increased echogenicity within normal liver parenchyma.

Diffuse Disease: Focal Sparing

  • Focal sparing should be suspected in patients exhibiting “mass-like” hypoechoic areas in a liver that is otherwise increased in echogenicity.

  • Common Locations:

    • Anterior to the gallbladder

    • The portal vein

    • Periportal region of the medial segment of the left lobe of the liver.

Viral Hepatitis

  • Definition:

    • Viral hepatitis is an inflammatory and infectious disease of the liver.

  • Causes:

    • Includes local infections (e.g., viral hepatitis, infectious mononucleosis, amebiasis) and reactions to chemical or drug toxicity.

  • Pathophysiology:

    • Inflammation impairs hepatocyte function, and necrosis may cause obstruction of blood and bile flow leading to further impaired liver cell function.

Types of Viruses Causing Hepatitis

  • Hepatitis A Virus (HAV):

    • Spread via the orofecal route.

    • Generally causes an acute infection leading to either complete recovery or death from acute liver failure.

  • Hepatitis B Virus (HBV):

    • Spread through infected blood transfusions, needle sharing, sexual contact, and even kissing.

  • Hepatitis C Virus (HCV):

    • Transmission mainly through blood.

Symptoms of Viral Hepatitis

  • Symptoms initially mimic flu-like illness and include:

    • Loss of appetite

    • Nausea and vomiting

    • Fatigue

  • Complications:

    • Acute hepatic necrosis

    • Chronic hepatitis

    • Portal hypertension

    • Cirrhosis

    • Hepatocellular carcinoma (HCC).

Acute Hepatitis

  • Recovery typically occurs within 4 months.

  • Complications Include:

    • Massive necrosis

    • Liver failure

  • Sonographic Findings:

    • The liver may appear normal, but portal vein (PV) borders may be more prominent, known as the “starry sky sign.”

    • Slightly increased echogenicity.

    • Hepatosplenomegaly.

Chronic Hepatitis

  • Defined as hepatic inflammation lasting beyond 6 months.

  • Causes:

    • Viral, metabolic, autoimmune, or drug-induced factors.

    • Types:

    • Chronic Persistent Hepatitis:

      • Benign, self-limiting process.

    • Chronic Active Hepatitis:

      • Typically leads to cirrhosis and liver failure.

  • Signs and Symptoms:

    • Nausea, anorexia, weight loss, tremors, jaundice, dark urine, fatigue, varicosities.

Chronic Hepatitis: Ultrasound Findings

  • Liver parenchyma appears coarse with diminished brightness of the portal triads.

  • Attenuation: Can be observed.

  • Fibrosis might show as posterior “shadowing.”

Cirrhosis

  • Cirrhosis is a chronic degenerative condition of the liver:

    • Characteristics:

    • Lobes are covered with fibrous tissue.

    • Parenchyma degenerates.

    • Lobules infiltrated with fat, leading to parenchymal necrosis and diffuse fibrosis, resulting in architectural disorganization.

Types of Cirrhosis

  • Micronodular Cirrhosis:

    • Most commonly caused by chronic alcohol abuse.

  • Macronodular Cirrhosis:

    • Typically caused by chronic viral hepatitis or other infections.

  • Other causes include biliary cirrhosis, Wilson’s disease (copper metabolism issues), primary sclerosing cholangitis, and hemochromatosis (iron deposition in the liver).

Symptoms of Cirrhosis

  • Acute Cirrhosis:

    • May be asymptomatic or present with:

    • Nausea

    • Flatulence

    • Ascites

    • Light-colored stools

    • Weakness

    • Abdominal pain

    • Varicosities

    • Spider angiomas

  • Chronic Cirrhosis:

    • Symptoms may include nausea, anorexia, weight loss, jaundice, dark urine, fatigue, varicosities, liver shrinkage, and progression to liver failure and portal hypertension.

Laboratory Tests for Cirrhosis

  • Increase in:

    • Lactic acid dehydrogenase

    • Alkaline phosphatase

    • AST (aspartate aminotransferase)

    • ALT (alanine aminotransferase)

    • Direct bilirubin

    • Other Findings:

    • Leukopenia

    • Hypoproteinemia

    • Jaundice

    • Gastrointestinal bleeding

    • Edema

Ultrasound Appearance of Cirrhosis

  • Observations include:

    • Increased echogenicity

    • Increased attenuation

    • Reduction in liver size

    • Coarse hepatic parenchyma

    • Decreased vascular markings associated with acute cirrhosis

    • Splenomegaly with ascites

    • Increased nodularity

    • Signs of portal hypertension

Complications of Cirrhosis

  • Liver cell failure

  • Portal hypertension (PHT)

  • Ascites

  • Development of hepatoma (liver cancer)

  • Development of collateral circulation (varices)

Cirrhosis: Ultrasound Characteristics

  • In the early stages of cirrhosis, hepatomegaly is the first finding.

  • As cirrhosis advances, the liver's right lobe volume decreases; the left and caudate lobes may enlarge.

  • Early signs include hepatomegaly and decreased vascularity.

Doppler Characteristics of Cirrhosis

  • The hepatic vein velocity waveform reflects the hemodynamics of the right atrium.

  • A normal waveform shows a triphasic pattern with two large antegrade (forward) diastolic/systolic waves and a small retrograde wave corresponding to the atrial kick.

  • In compensated cirrhosis (without portal hypertension), the Doppler waveform becomes abnormal, with luminal narrowing and increased velocities and turbulence.

Portal Venous Hypertension

  • Elevated portal venous pressure characterized by the following:

    • Portal vein pressure >10 mmHg

    • Direct portal vein pressure exceeding 5 mmHg greater than inferior vena cava pressure

    • Splenic vein pressure >15 mmHg, portal vein pressure can be >30 cm.

    • Main portal vein (MPV) diameter >13 mm suggests portal hypertension.

Pathophysiology and Consequences of Portal Hypertension

  • Collateral Venous Formation:

    • Collateral veins connect to systemic veins to relieve pressure, forming varices.

    • Common collateral formations include gastric veins (coronary veins), esophageal veins, splenorenal, gastrorenal, retroperitoneal, hemorrhoidal, or intestinal veins.

    • Rupture of these collateral veins can lead to massive bleeding, which can be fatal.

Causes of Portal Hypertension

  • Most Common Causes:

    • Cirrhosis (most common intrahepatic cause with increased resistance to flow)

    • Hepatitis, tumors (neoplastic), arteriovenous fistulae

    • Diffuse metastatic liver disease

    • Thrombotic diseases of the inferior vena cava and hepatic veins (Budd-Chiari syndrome)

    • Constrictive pericarditis and other right-sided heart conditions, tricuspid regurgitation, trauma, or compression/thrombosis of the hepatic veins.

Hepatic Vascular Flow Abnormalities: Portal Venous Hypertension

  • Observations on Ultrasound:

    • Hepatosplenomegaly in advanced cirrhosis

    • Decreased vascularity, ascites presence

    • Thickened gallbladder wall accentuated by ascitic fluid

Five Types of Portosystemic Venous Collaterals

  1. Gastroesophageal Varices:

    • Most common, connecting distal esophagus (esophageal veins) and gastric fundus (gastric veins); may lead to life-threatening GI hemorrhage.

  2. Recanalized Umbilical Vein:

    • Reopening to function as a collateral from left portal vein to the epigastric vein leading to the IVC.

  3. Splenorenal Varices:

    • Connection between splenic and renal veins, typically featuring tortuous collateral veins.

  4. Intestinal Varices:

    • Vascular connections in retroperitoneal structures such as the colon, duodenum, and pancreas.

  5. Rectal Veins:

    • Pathways connecting inferior mesenteric vein (IMV) to rectal veins and systemic tributaries.

  • The most common collateral pathways are through the coronary and esophageal veins.

Portal Venous Hypertension: Collaterals

  • The umbilical vein may become recanalized as a secondary response to portal hypertension, visible in longitudinal imaging near the midline near the left lobe of the liver.

Portal Hypertension - Secondary Causes

  • Primary Presentations:

    • Ascites, splenomegaly, and possible bleeding varices.

    • Portal vein thrombosis can arise from trauma, sepsis, cirrhosis, or hepatocellular carcinoma.

Shunting in Portal Hypertension

  • Types of Shunts:

    • Portacaval Shunt:

    • Connects the main portal vein at the superior mesenteric vein-splenic vein confluence to the IVC.

    • Mesocaval Shunt:

    • Attaches the mid-distal superior mesenteric vein to the IVC, may be difficult to visualize due to bowel gas.

    • Transjugular Intrahepatic Portosystemic Shunt (TIPS):

    • Percutaneous creation involving metallic expandable stents, but may develop stenosis at hepatic vein or shunt levels.

Budd-Chiari Syndrome

  • Description:

    • Caused by thrombosis of the hepatic veins or inferior vena cava (IVC); characterized by abdominal pain, massive ascites, and hepatomegaly with a poor prognosis.

  • Classification:

    • Primary type results from congenital obstruction by membranes; secondary type is caused by thrombosis from various risk factors, including long-term oral contraceptive use and certain cancers.

  • Symptoms Include:

    • Ascites, abdominal pain, hepatosplenomegaly, jaundice, vomiting, diarrhea, edema, or albuminuria.

Diffuse Abnormalities of the Liver Parenchyma: Biliary Obstruction

  • Proximal Obstruction Causes:

    • Gallstones

    • Carcinoma of the common bile duct

    • Metastatic tumor invasion of the porta hepatis

    • Common duct stricture

    • Passive hepatic congestion secondary to congestive heart failure

  • Clinically, patients may exhibit jaundice and pruritus.

Biliary Obstruction: Imaging Characteristics

  • Ultrasound Findings for Proximal Obstruction:

    • Demonstrates gross pathology, potential obstruction by gallstones, or tumors, leading to dilated intrahepatic ducts.

Biliary Obstruction: Distal Causes

  • Causes of Distal Obstruction:

    • Stones in the common duct

    • Extrahepatic mass compressing the CBD (tumor in the head of the pancreas)

    • Common duct stricture

  • Clinical Signs:

    • Patients may present symptoms including common duct stones, jaundice, and pruritus, often with increased direct bilirubin and alkaline phosphatase levels.