Category:Liver - Inflammatory Pathology

Parasitic

Many parasites pass through the liver as part of their life cycle within the host

Some migrate further to other organs while others remain in liver tissue, especially the bile ducts

Most migrating parasites escape the liver but occasionally some may die and provoke a granulomatous reaction that may calicfy later

The following are types of parasites causing liver lesions:

Nematodes

• these cause damage during migration through the liver

Ascaris suum

• Ascariasis
• 'milk spot' liver
• pigs
• common incidental finding at post mortem examination
• affected livers are condemned at meat inspection

Gross

• initial haemorrhagic tracts through the liver attributed to the migration of ascarid larvae
• later stages show fibrosis of these tracts as poorly defined, diffuse, white spots on the capsular surface

Microscopically

• initial haemorrhage and necrosis of parenchyma along the tracts
• later repair by fibrous tissue at foci
• inflammatory cell response contains many eosinophils, as well as lymphocytes and macrophages

Strongyles

• horses
• it is common to find fibrous tags incidentally on the liver surface and adjacent diaphragm
• these are remnants of fibrous repair following the egress of the parasites from the liver

Cestodes

• tapeworms
• have both intermediate and final hosts in their life cycle
• main expression in the UK are the encysted forms that utilise the liver and other organs in intermediate hosts

Taenia hydatigena

• the most important species
• final host
  • dog
  • alimentary tract
• intermediate host
  • ruminant, horse, or pig
• life cycle is completed when the carnivore eats the tissues of the intermediate host containing the cysts
• the intermediate stage - Cysticercus tennuicollis
  • fluid filled cysts on the surface of the liver and in the peritoneal cavity

NB: other Taenia species have muscle and brain as preferred sites in the intermediate hosts

Some can infect humans - zoonoses

Echinococcus granulosus

• Hydatid Disease
• final host
  • dog, fox, and other canids
• intermediate host
  • sheep most commonly affected
  • ox and horses

NB: can also affect man - zoonosis

• hydatids - the cyst form
  • develops from the ova
  • occur in the lung and liver
  • cysts are usually multiple
  • 5-10cm in diameter
  • contain a clear fluid with numerous scolices or "hydatid sand"
  • the small calcified lesions that are sometimes present in the liver of sheep may represent degenerate hydatid cysts
  • can be very prevalent in some geographical areas

Trematodes

• flukes are important pathogens of the liver
• Fascioliasis is among the most important parasitic conditions of sheep and cattle and is common

Fasciola hepatica

• common liver fluke
• intermediate host
  • aquatic snails
  • therefore infestation is more common in damp or poorly drained pastures
• final host
  • cattle and sheep
• can cause severe haemorrhagic liver damage
• death in heavy infestations in sheep during migratory phase (1 month) through the liver tissue
• recovered animals will have scarred livers
• more commonly associated with chronic bile duct inflammation - cholangitis [need link to below]
  • the adults live in the bile ducts

Acute Fascioliasis

• acute disease associated with immature fluke migration through the liver
• occurs in late autumn and winter
• severity of outbreaks depend on a number of epidemiological factors
• the liver of animals which die of this disease will be
  • enlarged
  • haemorrhagic
  • honeycombed with the tracts of migrating flukes
    • tracts become filled with blood and degenerate hepatocytes later infiltrated with eosinophils, lymphocytes and replaced by fibrosis
  • surface is covered with a fibrinous peritonitis, especially the ventral lobe
  • subcapsular haemorrhages are frequent
  • rupture into the abdomen is not an uncommon finding

Chronic Fascioliasis

Gross

• liver is reduced in size, unevenly
  • left lobe is most severely affected with atrophy of the extremities
• hypertrophy may occur in some cases
  • dorsal lobe
  • this changes size and distorts shape of liver
• the surface will be uneven with areas of fibrous tissue replacing the cells damaged by the migrating flukes
• bile ducts
  • prominent thick protruding white bile ducts on the visceral surface spreading from the hilus to the left lobe
  • the bile ducts are dilated, black, and calcified on cut surface
  • numerous adult flukes can be expressed from the bile ducts
  • chronic cholangitis
  • 'pipe stem' appearance in cattle because bile ducts are very much thickened and often calcified
• bile
  • dark brown, thick, and gritty in consistency

NB: the fibrosis which occurs in the chronic stage is realted only partly to the healing of the migratory tracts and the rest may be related to the development of immunity and rechallenge

Microscopically

• reactive hyperplasia of the bile ducts
• substantial inflammatory cell infiltrate and peripheral fibrosis
• calcification of the chronically damaged tissue

Protozoal

Toxoplasmosis

• Toxoplasma gondii
• broad host range
• characterised by widespread necrosis in many organs
• liver lesions
  • appear as disseminated foci of necrosis with little or no inflammatory reactions
  • white or yellow foci are visible on the surface

Peliosis hepatica

• Dogs and cats
• Vasculoproliferative disorder – cystic, blood filled spaces in the liver , surrounded by fibromyxoid matrix containing inflammatory cells and dilated capillaries.
• Spaces may merge with hepatic sinuosoids.
• May be associated with Bartonella henselae infection.
• Natural host is the cat
• Transmitted between cats by fleas
• Cause of cat-scratch fever and bacillary angiomatosis in humans

Lobular dissecting hepatitis

• Rare cause of chronic liver failure in young dogs
• Less than 5yrs of age
• Standard poodle overrepresented
• Gross findings:
  • Micronodular microhepatica, ascites, numerous portosystemic shunts
• Histology:
  • Hepatic architecture disrupted by collagen and reticulin fibres separating the hepatic lobules into small clusters and individual cells
  • Hepatocytes mutlifocally swollen, lightly eosinophilic, some binucleated.
  • Variable nodular regeneration.
  • Scattered necrotic cells and occasional foci of inflammation.
• Cu2+ accumulation not a consistent finding.
• Aetiology – possibly a specific reaction pattern in neonatal/juvenile liver .
• Differentials:
  • Copper toxicity
  • Copper storage disease
  • Aflatoxin
  • Infectious diseases such as Leptospria spp. and CAV-1.

Hepatitis in cats

• 2 main types
  • cholangiohepatitis
    • cholangitis
    • periportal hepatocellular necrosis
    • neutrophils in the portal areas
    • acute or chronic.
    • Usually male, pure bred
    • Cats more ill than lymphocytic portal hepatitis.
    • Higher ALT and serum bilirubin levels.
  • Lymphocytic portal hepatitis
    • infiltration of portal areas with lymphocytes and plasma cells
    • no cholangitis
    • no periportal hepatocellular necrosis.