Last updated on April 30, 2020 at 21:18
The liver is the largest parenchymal organ, with a weight between 1000-1300 g. The most important jobs of the liver are synthesis, detoxication and excretion.
Impaired blood flow into the liver
1. Hepatic artery infarct
Infarcts in the liver are rare, due to the double blood supply of to the liver. Therefore, an interruption of the main hepatic artery does not always cause ischemic necrosis because the retrograde arterial flow through the accessory vessels and portal venous supply may sustain liver parenchyma. However, this doesn’t apply for a transplanted liver where a complication can be hepatic artery thrombosis. The transplanted liver parenchyma will die.
Thrombosis or compression of intrahepatic branches of the hepatic artery may also result in localized parenchymal infarct.
2. Portal vein obstruction and thrombosis
Extrahepatic portal vein obstruction can arise from the following scenarios:
- Pancreatitis which causes a thrombosis in the splenic vein that moves into the portal vein.
- Thrombogenic diseases
- Postsurgical thromboses
- Cirrhosis – does not obstruct directly but slows down the blood flow which increases the risk for thrombus formation.
Occlusion of the portal vein or its branches give symptoms like abdominal pain, other manifistations of portal hypertension like esophageal varices. Ascites is rare because the block is presinusoidal, but when present are often massive and intractable.
Intrahepatic portal vein occlusions do not cause an ischemic infarction when acute but result in a sharply demarcated area of red-blue discoloration, called infarct of Zahn. There is no necrosis but congestion of sinusoids and atrophy of hepatocytes.
Impaired blood flow through the liver – Passive congestion and centrilobular necrosis
The most common cause of impaired blow flow through the liver is by far cirrhosis. Physical occlusion of sinusoids (Sickle cell) or DIC can also occur.
Passive congestion of the liver (nutmeg liver) and central haemorrhagic necrosis are hepatic manifestations of systemic circulatory disorders. Right-sided cardiac failure, like in cor pulmonale, leads to congestion of the liver. Chronic congestion of the liver causes the morphology nutmeg liver, or hepar moschatum. If a patient with nutmeg liver also develops acute left ventricular failure there will be central haemorrhagic necrosis as well. You can study more about these conditions in the pathology 1 section.
Nutmeg liver doesn’t cause jaundice or liver disfunction but can be detected by a small elevation in serum aminotransferase levels.
Manifestations of impaired blodflow through the liver can be ascites (cirrhosis), esophageal varices (cirrhosis), hepatomegaly and as previously mentioned elevated levels of serum transaminases.
Hepatic vein outflow obstruction
1. Hepatic vein thrombosis – Budd-Chiari syndrome
The Budd-Chiari syndrome is a very rare condition (1 in one million) that results from occlusion of two or more major hepatic veins. Occlusion causes the congestion of the liver, causing hepatomehaly, ascites and portal hypertension.
The risk factors for thrombosis here are usual risk factors for thrombus formation or mechanical obstruction:
- Hypercoagulable state
- Polycythaemia vera (50% of cases)
- Oral contraceptives
- Hypercoagulability due to cancer
- Invasion of cancers like renal cell carcinoma into the hepatic vein
The liver will swell and the capsule around it will become tense. The liver itself will look red-purplish. Histologically, we can see centrilobular congestion (nutmeg liver appearance) with centrilobular necrosis. The mortality is high.
Clinical findings in patients with these are hepatomegaly, ascites, and abdominal pain.
2. Sinusoidal obstruction syndrome
Sinusoidal obstruction syndrome, also called hepatic venooclusive disease is caused by damage to the sinusoidal epithelium, most commonly due to chemotherapy or radiation. Nowadays it’s often seen in people who undergo chemotherapy before a bone marrow transplant (as this chemotherapy is very intensive).
The damaged endothelium cells will slough and form thrombi, which block the sinusoidal flow. RBCs also spill into the space of Disse as there is no endothelium holding them back, while the damaged endothelium also cause proliferation of stellate cells and fibrosis of terminal branches of the hepatic vein.
The clinical presentation is similar to that of Budd-Chiari syndrome, involving hepatomegaly, ascites and portal hypertension.
The neonatal hepatitis is a group of disorders in neonates which are characterized by:
- Hepatocellular dysfunction
- Conjugated hyperbilirubinemia
They all have very similar morphology as well:
- Balloonisation or focal necrosis of hepatocytes
- Multinucleated hepatocytes
- Lymphocytic infiltration in the portal area
- Proliferation of bile ducts
The neonatal hepatitis can be caused by several disease, like e.g. TORCH or metabolic causes. Let’s take a look at them.
- TORCH infections
- Metabolic causes
- Alfa1-antitrypsin deficiency
- Wilson disease – where excess copper is stored various tissues of the body, like the liver.
- Bile duct anomalies
- Atresia of intra- or extrahepatic bile duct.
- Alagille syndrome – autosomal dominant syndrome where there are too few bile ducts.
- Progressive familiar intrahepatic cholestasis (PFIC), which causes cholestasis due to defects in the biliary epithelial transporters.
Cholangitis is an acute infection of the biliary tree, almost always caused by bacterial infection. It is usually caused by anything that can obstruct the bile flow, but most commonly choledocholithiasis, gall stones in the common bile duct. Other reasons for this can be surgery of the biliary tree, tumors and acute pancreatitis. The bacteria usually enter the biliary tract via the Sphincter of Oddi rather than through blood, and results in an ascending cholangitis, where the bacteria “climb upwards” in the biliary tree until the intrahepatic biliary ducts. The usual pathogens are:
- E. coli
The symptoms of cholangitis include fever, chills, abdominal pain and jaundice. If the cholangitis is severe enough, it develops into suppurative cholangitis where the purulent bile expands the bile ducts and gives a high risk of liver abscess formation and sepsis. Treatment is needed and includes antibiotics and drainage of the bile ducts.
Liver abscesses in developing countries are often caused by parasites. Liver abscesses in the western countries are caused by bacteria. The bacteria can reach the liver by ascending infection in the biliary tract, through vascular seeding from the GI-tract, direct invasion into the liver from a nearby source or by a penetrating injury. The pathogens that can cause this are many, and its often more than one organism involved. The most common bacteria are:
- E. coli
The most common causes of bacterial liver abscesses are:
- Ascending infections from the biliary tract – most common
- Spreading of bacteria from the GI tract via the portal vein
- Systemic bacteraemia (sepsis)
Bacterial hepatic abscesses can occur alone or as multiple lesions, and their sizes can range from millimetres to many centimetres. The morphology is as for any pyogenic abscess: liquefactive necrosis with neutrophil infiltration.
Patients with a liver abscesses have fever and pain in the right upper quadrant. They also have tender hepatomegaly and can develop jaundice if the reason for the abscess is biliary obstruction. Antibiotics and surgical drainage are needed. Non-treated liver abscesses have a high mortality rate!
A gigantic liver abscess for you to look at
Echinococcus cysts in the liver
Echinococcus or hydatid cysts in the liver is a consequence of consuming something contaminated by echinococcal tapeworm’s eggs. An example of contamination is drinking water which is infested by dog faeces, or not washing your hands after petting a dog or cat and then touching food. When the eggs are ingested, they hatch in the intestines and the adult tapeworms penetrate the intestinal wall. This gives them the ability to travel with the blood stream or the lymphatic circulation, and they often end up in the liver where they die and form a hydatid cyst. This cyst can grow and compress the structures in the liver and around, destroying the liver parenchyma.
The incubation time is long, and the cyst shows usually no symptoms. However, the patients may experience pain in the upper right quadrant and hepatomegaly. Rupture of these cysts can cause allergic reactions and death, so surgery is needed to remove them as soon as possible.
These cysts look solid on imaging and can therefore be mistaken for a tumor.
These cysts are often solitary, but they can be multiple. This occurs if the parasites can spread throughout the biliary tree before dying.
Drugs are an important cause of liver injury, and many accepted drugs have been withdrawn from the market because they caused severe hepatopathies. Some drugs are hepatotoxic only in big doses and must be monitored closely by the doctor. We distinguish between direct and indirect hepatotoxic substances.
Direct hepatotoxic substances are called that because their metabolites directly cause damage to the liver. However, we can predict the damage, and know the dose that can be given without causing damage – their toxicity is dose dependent. Also, some persons are more exposed to develop diseases and injuries from these drugs than others. The onset of symptoms of injury is also short.
- Anabolic steroids
- Paracetamol (Acetaminophen)
Indirect hepatotoxic substances can cause damage because their substances can serve as haptens, initiating an immune reaction. They can also cause damage by altering the metabolism of the liver. This toxicity is not dose-depended so it’s hard to predict the dose and how an individual will react to the drug. There is also 1-2 weeks latency before the symptoms shows, and other allergic symptoms can appear as well.
- Anabolic steroids
10. Diseases of the appendix and the peritoneum
12. Acute viral hepatitis (aetiology, pathomorphology, complicated forms)