Difference between revisions of "Liver Necrosis"

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== Introduction ==
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====Causes====
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Hepatocytes are the epithelial cells of the liver, and these are the main targets of most liver diseases. They can ultimately undergo necrosis, a form of cell death, after lethal injury. This can occur following severe metabolic disturbances, toxic insults, nutritional deficiencies and through the action of micro-organisms.
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*severe metabolic disturbances [as seen in degenerative pathology link?]
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<br>
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*toxic substances [link?]
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Despite many types of injury that the liver is subjected to, the resultant necrosis occurs in one of three patterns:
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*nutritional deficiencies
 +
*action of micro-organisms
  
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== Random Necrosis (Focal)==
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====Histological patterns====
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In this form of necrosis, there is no distinct pattern of lesions - small foci of necrosis are randomly scattered throughout the liver, and may be either microscopic or just visible to the naked eye. They can result from a variety of insults such as - systemic viral, bacterial and parasitic infections, or as a result of bacteria being absorbed from the gut.
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*[[Liver - Anatomy & Physiology|Liver]] cell necrosis has been classified on an anatomic basis with reference to the distribution of the lesion
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<br>
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=====Random foci (focal)=====
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Examples of conditions that result in random focal hepatic necrosis include:
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*microscopic foci of necrosis not related to any particular part of the [[Liver - Anatomy & Physiology|liver]] lobule
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*[[Equine Herpesvirus 1|Equine herpes virus 1]] infection found in aborted foetuses
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*can be due to a variety of insults
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*Septicaemia in association with [[Salmonellosis|salmonellosis]], tularaemia and [[Listeriosis|listeriosis]]
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**systemic viral, bacterial,and parasitic infections
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*[[Toxoplasmosis - Cat and Dog|Toxoplasmosis]] in dogs and cats
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**result of bacteria being absorbed from the gut
 +
*examples
 +
**Equine herpes virus infection  
 +
***in aborted foetuses
 +
**Salmonellosis
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***in calves
 +
**Toxoplasmosis (miliary)
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***in dogs and cats
  
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If grossly visible, necrotic foci appear as discrete white or red foci that range from one to many millimetres in diameter.
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=====Zonal necrosis=====
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*necrosis occurring mainly in a part of the lobule and further subdivided according to whether the lesions are situated centrally, peripherally, or in the mid-zone of the lobule
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== Zonal Necrosis ==
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*due to anoxia
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This type of change affects hepatocytes in defined anatomic regions of the liver lobule:
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======Periacinar (centrilobular)======
  
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'''Periacinar (Centrilobular)'''<br>
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*most common
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This is the most common type of zonal necrosis and occurs mainly due to the fact that hepatocytes in this central zone are furthest away from the incoming blood supply. They are therefore more susceptible to hypoxia. Additionally, they contain the greatest concentration of cytochrome p450 enzymes that metabolise substances into more reactive metabolites capable of killing the hepatocytes. Therefore toxic insults and conditions leasing to hypoxia commonly produce this pattern of necrosis. Some viral conditions, however, also result in centrilobular necrosis, such as '''[[Infectious Canine Hepatitis]] (ICH)'''. This is a highly infectious disease of young dogs caused by canine adenovirus-1. It is now rare in the UK and US due to effective vaccination protocols.
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*main reason is because the hepatocytes in this zone are furthest away from the incoming blood supply
 +
**therefore less oxygenated and relatively anoxic
 +
*reported to contain the greatest number of enzymes responsible for metabolising sunstances to more toxic metabolites capable of killing the hepatocytes
 +
*hypoxic states and toxic substances predominate in this type of necrosis
 +
*some viral conditions cause this necrosis
 +
**eg Infectious Canine Hepatitis
 +
*poisons
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**eg carbon tetrachloride
  
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'''Midzonal'''<br>
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======Midzonal======
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This pattern of necrosis is rare in animals although is mainly seen in horses and pigs with aflatoxicosis. It is also seen in people suffering from 'Yellow Fever'.
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*rare
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*in pigs with alfatoxicosis
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*'Yellow Fever' in man
  
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'''Periportal (Centroacinar)'''<br>
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======Periportal (centroacinar)======
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This is another uncommon pattern of necrosis that only involves a region around the central vein. It is caused by direct-acting hepatotoxins, and is seen in cases of phosphorus poisoning.
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*rare
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*eg phosphorous poisoning
  
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Regardless of the zone affected, grossly the liver is pale, friable, slightly enlarged with rounded edges, and has an enhanced lobular pattern.
 
  
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=== Massive Necrosis ===
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=====Massive necrosis=====
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This pattern does not imply necrosis of the whole liver, but rather describes necrosis that spans an entire lobule or adjacent lobules. All hepatocytes within the affected lobule(s) are necrotic.
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*necrosis of large areas of [[Liver - Anatomy & Physiology|liver]] cells comprising many lobules (complete acinus or several acini) and sometimes involving almost the whole organ
 +
*some cases of ICH infection or carbon tetrachloride poisoning, the severity of the injury replacing the zonal pattern
 +
======Subacute cytolytic necrosis======
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*a condition in the dog
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*aetiology is entirely unknown
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*Clinical
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**acute abdominal pain
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**collapse
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**invariably jaundice
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*Gross
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**[[Liver - Anatomy & Physiology|Liver]] is normal or reduced in size
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*Microscopically
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**severe necrosis
  
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Since all hepatocytesin the lobule are affected, regeneration of these regions is not possible, and affected lobules collapse. In acute stages, the liver may be enlarged or swollen due to congestion. Later, it may reduce in size as a result of scarring that occurs subsequent to lobular collapse (post-necrotic scarring).
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======''Hepatosis dietica''======
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*similar condition to subacute cytolytic necrosis
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'''''Hepatosis dietica''''' is one condition that results in massive necrosis due to vitamin E and selenium deficiency. This occurs in rapidly growing pigs that are fed on large quantities of grain concentrates, or poor quality or low quantity protein supplements. The exact pathogenesis is still poorly understood, but the resultant nutritional deficiencies of selenium and Vitamin E are considered to generate free radicals that result in liver necrosis.
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*occurs in rapidly growing pigs
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*related to diet
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{{Learning
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**fed on large quantities of grain concentrates
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|flashcards = [[Liver_Flashcards_-_Pathology|Liver Pathology Flashcards]]
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**poor quality or low quantity protein supplements
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}}
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*Cause
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**nutritional deficiencies of selenium and Vitamin E, and probably amino acids
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== References ==
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**triggering mechanism is environmental stress[[Category:Liver_-_General_Pathology]]
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Blood, D.C. and Studdert, V. P. (1999) '''Saunders Comprehensive Veterinary Dictionary '''(2nd Edition), '' Elsevier Science.''
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[[Category:To_Do_-_Clinical]]
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<br>
 
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Ettinger, S.J, Feldman, E.C. (2005) '''Textbook of Veterinary Internal Medicine '''(6th edition, volume 2),'' W.B. Saunders Company.''
 
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<br>
 
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Fossum, T. W. et. al. (2007) '''Small Animal Surgery''' (Third Edition), '' Mosby Elsevier.''
 
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<br>
 
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Maxie, M.G. (2007) '''Pathology of Domestic Animals''' Volume 2 (Fifth Edition), ''Elsevier Saunders''.
 
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<br>
 
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McGavin, M.D. and Zachary, J.F. (2007) '''Pathologic Basis of Veterinary Disease''' (Fourth Edition), ''Elsevier Mosby''.
 
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<br>
 
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Nelson, R.W. and Couto, C.G. (2009) '''Small Animal Internal Medicine '''(Fourth Edition), ''Mosby Elsevier. ''
 
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<br>
 
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Smyth, B (2008) '''Alimentary System Study Guide''''', Royal Veterinary College''.
 
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{{Nicky Parry
 
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|date = September 09, 2011
 
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}}
 
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==Webinars==
 
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<rss max="10" highlight="none">https://www.thewebinarvet.com/gastroenterology-and-nutrition/webinars/feed</rss>
 
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[[Category:Liver_-_General_Pathology]]
 
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[[Category:Nicola Parry reviewed]]
 

Revision as of 20:49, 28 June 2010

Causes

  • severe metabolic disturbances [as seen in degenerative pathology link?]
  • toxic substances [link?]
  • nutritional deficiencies
  • action of micro-organisms

Histological patterns

  • Liver cell necrosis has been classified on an anatomic basis with reference to the distribution of the lesion
Random foci (focal)
  • microscopic foci of necrosis not related to any particular part of the liver lobule
  • can be due to a variety of insults
    • systemic viral, bacterial,and parasitic infections
    • result of bacteria being absorbed from the gut
  • examples
    • Equine herpes virus infection
      • in aborted foetuses
    • Salmonellosis
      • in calves
    • Toxoplasmosis (miliary)
      • in dogs and cats
Zonal necrosis
  • necrosis occurring mainly in a part of the lobule and further subdivided according to whether the lesions are situated centrally, peripherally, or in the mid-zone of the lobule
  • due to anoxia
Periacinar (centrilobular)
  • most common
  • main reason is because the hepatocytes in this zone are furthest away from the incoming blood supply
    • therefore less oxygenated and relatively anoxic
  • reported to contain the greatest number of enzymes responsible for metabolising sunstances to more toxic metabolites capable of killing the hepatocytes
  • hypoxic states and toxic substances predominate in this type of necrosis
  • some viral conditions cause this necrosis
    • eg Infectious Canine Hepatitis
  • poisons
    • eg carbon tetrachloride
Midzonal
  • rare
  • in pigs with alfatoxicosis
  • 'Yellow Fever' in man
Periportal (centroacinar)
  • rare
  • eg phosphorous poisoning


Massive necrosis
  • necrosis of large areas of liver cells comprising many lobules (complete acinus or several acini) and sometimes involving almost the whole organ
  • some cases of ICH infection or carbon tetrachloride poisoning, the severity of the injury replacing the zonal pattern
Subacute cytolytic necrosis
  • a condition in the dog
  • aetiology is entirely unknown
  • Clinical
    • acute abdominal pain
    • collapse
    • invariably jaundice
  • Gross
    • Liver is normal or reduced in size
  • Microscopically
    • severe necrosis
Hepatosis dietica
  • similar condition to subacute cytolytic necrosis
  • occurs in rapidly growing pigs
  • related to diet
    • fed on large quantities of grain concentrates
    • poor quality or low quantity protein supplements
  • Cause
    • nutritional deficiencies of selenium and Vitamin E, and probably amino acids
    • triggering mechanism is environmental stress
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