2.10 Liver and pancreas pathology

Liver blood flow

• 75% portal vein (poorly oxygenated)

• 25% hepatic artery (oxygenated)

How does blood and bile travel in the hexagonal lobule?

• Blood travels from portal tracts into central vein (edge to center)

• Bile travels from central hepatocytes into peripheral bile ducts (center to edge)

3 hepatic lobule zones (outer to inner)

• Periportal

• Midzonal

• Centrolobular (surrounds central vein)

List 2 pathologies that the centrilobular zone is most prone to.

• Hypoxic injury → blood travels from peripheral to center 

• Toxicity → contains lots of enzymes (cytochrome P450s)

Bile duct epithelium type

Cuboidal or columnar

Connective tissue holding portal triad together

Limiting plate

Why does portosystemic shunt cause liver atrophy?

Liver receives growth factors from blood nutrients

Describe how acquired portosystemic shunts are formed. (3) How does it look microscopically? (2) What pathology does it result in? (1)

• Older animals → secondary to fibrosis

• Blood cannot get into liver → resistance in fibrotic sinusoids

• Formation of lots of thin walled capillaries connecting portal vein and rest of venous circulation

• Thick pink walls of multiple small hepatic arterioles in microscopy

• Distorted structure, cannot see thick portal vein

• Hepatic encephalopathy → ammonia bypasses liver

Other than portosystemic shunts, name 5 developmental disorders of the liver.

• Congenital cysts (most commonly biliary)

• Displacement of liver → portal vein twists → necrosis

• Tension lipidosis (attached to body wall) → restricts blood flow

• Telangiectasia (dilation of blood vessels)

  • dark spots → focal sinusoidal dilation

  • mistaken for melanosis

• Capsular fibrosis

How do you distinguish between hepatocytomegaly and congestion causing liver enlargement?

• Hepatocytomegaly - dry cut surface

• Congestion - blood pours out of it

How does hydropic vacuolation happen in the liver?

• Failure of energy supplying pumps (hypoxia, mild toxic damage, metab stress)

• Nonspecific and reversible

Name the most common cause of glycogen accumulation.

Endogenous/exogenous glucocorticoids

• Cushing’s 

• Steroids

List 5 causes of liver lipidosis.

• Starvation (most common cause in horse)

• Massive energy demand (pregnancy or lactation)

• Metabolic diseases (diabetes → ketosis, pregnancy toxaemia)

• Obesity (less common)

• Abnormal hepatocyte function

Cytology of lipidotic liver

Crisp, well defined lipid vacuoles that displace nucleus to edge of cell

How do you grossly detect hepatic lipidosis?

Liver floats in formalin due to lots of fat

How do you detect amyloidosis in the liver? (3)

• Large, pale orange, friable liver

• Microscopically - homogenous acidophilic material between hepatocytes

• Congo red → apple green birefringence under polarisation

What is zonal liver injury often associated with?

Ischaemia or toxic damage

What is focally extensive liver injury often associated with?

Bacterial injury (big infection)

What are random white nodules of liver injury often associated with?

Viral or bacterial damage

• white nodules are small pockets of inflammatory cells

How is the liver different in acute V chronic necrosis?

• Acute - liver is soft and friable

• Chronic - liver is firm and fibrotic

How is lymphoma mediated cholangitis different from lymphocytic cholangitis?

• Lymphocytic → bile duct is regenerating

• Lymphoma → bile duct is destroyed

4 ways of hepatitis progression

• Regeneration (complete resolution)

• Repair (fibrosis + scarring)

• Encapsulation by abscessation

• Persistence 

3 causes of viral hepatitis

• Adenovirus (canine infectious hepatitis)

• Herpesvirus (EHV1, IBR/P/V, Aujeskys)

• FIP (mutated coronavirus)

List the signs of infectious canine hepatitis. (4)

Adenovirus infection

• Intranuclear dark marginal bodies

• Widespread haemorrhage

  • Virus has tropism for endothelium

• Enlarged, reddened lymph nodes and tonsils

• Recovering animals - immune mediated uveitis + corneal opacity

Describe the microscopic lesions seen in hepatic herpesvirus infections.

Pink mass of protein with nuclear fragments, with intranuclear inclusion bodies outside the lesion

• Congealing of dying hepatocytes

Pathogen causing Tyzzer’s disease and 3 species affected

• Clostridium piliforme (piliformis)

• Foals (1-4 weeks)

• Rodents

• Immunosuppressed smallies

Tyzzer’s disease 2 microscopic lesions

• Intracellular bacteria (unusual for clostridium)

• Wheat sheaf colonies when stained with silver

Cattle specific salmonellosis

S. dublin

How does salmonella spread from gut to liver? What does it look like macroscopically and microscopically? What other pathology can be seen? (4)

• Macrophages carry salmonella from gut to liver

• Pale pinpoint white foci of liver necrosis - paratyphoid nodules

• Necrosis and mixed mononuclear cells

• Haemorrhagic or fibronecrotic ileitis

List 2 signs and 2 causes of acute liver intoxication.

• Decreased clotting factor synthesis → haemorrhage

• Icterus

• Cyanobacteria

• Iron and cresols

What does chronic liver intoxication normally cause? List 4 causes.

• Fibrosis and biliary hyperplasia

• Ragwort

  • Megalohepatocytosis - inhibition of mitosis

• Alflatoxins

• Copper

• Drugs

  • Primidone

  • Sulfonamides

  • Paracetamol

What does nodular hyperplasia look like and what animals does it commonly affect?

• Spherical nodules in liver - varied in colour, similar to rest of liver

• Benign hyperplasia in older dogs

Liver primary tumour

Hepatocellular adenoma or carcinoma

Biliary epithelium tumour and description

• Cholangiocellular carcinoma most common

• White, firm, umbilicate (pit in center), may resemble normal parenchyma

• If malignant - haemorrhage and necrosis

4 common metastatic tumours in the liver

• Carcinoma

• Sarcoma

  • Haemangiosarcoma

• Lymphoma

• Melanoma

Where does haemangiosarcoma metastasis in the liver usually originate from, what does it look like and what animals is it prevalent in?

• Spleen and right auricle

• Dark red and blood filled

• Large breeds of dogs