Cirrhosis
Introduction
Cirrhosis represents an “end-stage liver” - the final, irreversible result of diffuse hepatic disease, involving architectural disruption of the entire liver. Underlying chronic injury leads to loss of hepatic tissue with replacement fibrosis. Nodular regeneration occurs within regions of hepatic tissue in between fibrous tissue bands, giving rise to the characteristic multinodular gross appearance of this condition.
The three characteristic microscopic features of cirrhosis are:
- Nodular regeneration
- Fibrosis
- Bile duct hyperplasia
Bile duct hyperplasia around portal regions is a non-specific response to a variety of long-standing hepatic insults, but occurs especially in association with diseases that obstruct bile drainage.
Vascular abnormalities are also associated with cirrhosis. Anastomoses occur between the hepatic portal vein and systemic vasculature due to increased portal pressure. Additionally, vascular shunts can result within regenerative nodules, either between central and portal veins, or between hepatic arteries and central veins.
Causes of Cirrhosis
Some of the many possible causes of cirrhosis in animals include:
- Chronic right sided heart failure
- Chronic hepatitis
- Lobular dissecting hepatitis in dogs
- Hepatitis due to infectious canine hepatitis virus
- Chronic cholangitis or bile duct obstruction
- Chronic toxicity
- Pyrrolizidine alkaloid plants in herbivores
- Primidone anticonvulsants in dogs
- Inherited diseases of metal metabolism
Cirrhosis is usually the end result of multiple pathological processes, in particular cell death and active inflammation with fibrosis. Regardless of the original underlying aetiology, however, the end-stage liver can no longer perform its functions, and is therefore associated with clinical manifestations of hepatic failure.
Pathology
Gross
The liver is smaller than normal and firm to cut, firmness is due to the presence of fibrous tissue. It is pale, sometimes yellow in colour and contains a regenerating nodule that can be small and even in size with the liver having a finely granular appearance, or much larger, uneven in size, and the liver surface is deeply fissured and irregular.
Microscopically
The liver exhibits all 3 responses to injury:
- nodular regeneration of the parenchyma - haphazard regeneration of liver cells forming islands of new cells surrounded by condensed portal areas
- fibrosis - early cases show areas of fibrosis connecting two or more portal triads, later cases have prominent laying down of cartilage.
- biliary hyperplasia
References
Blood, D.C. and Studdert, V.P. (1999) Saunders Comprehensive Veterinary Dictionary (2nd Edition), Elsevier Science.
Ettinger, S.J. and Feldman, E.C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition), W.B. Saunders Company.
Maxie, M.G. (2007) Pathology of Domestic Animals Volume 2 (Fifth Edition), Elsevier Saunders.
McGavin, M.D. and Zachary, J.F. (2007) Pathologic Basis of Veterinary Disease (Fourth Edition), Elsevier Mosby.
Smyth, B (2008) Alimentary System Study Guide, Royal Veterinary College.