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==Introduction==

'''Portosystemic shunts (PSS)''' are anomalous vascular connections between the portal and systemic venous systems.  These vessels shunt blood from the '''hepatic portal vein''' (deriving from the stomach, intestines, [[Pancreas - Anatomy & Physiology|pancreas]] and [[Spleen - Anatomy & Physiology|spleen]]) directly into '''systemic venous system''', bypassing the [[Liver - Anatomy & Physiology|liver]].

| '''Portocaval Shunt<br>

'''Patent Ductus Venosus<br>

'''Portosystemic Vascular Anomalies'''

|-}

Portosystemic shunts may be '''congenital''' or they may be '''acquired''' with diseases that cause portal hypertension.  In the developing embryo, the cardinal veins form the systemic abdominal veins (the caudal vena cava, azygos, renal and gonadal veins) whereas the vitelline veins form the hepatic sinusoids, the portal vein and its tributaries, of which the largest are the left gastric, splenic, cranial and caudal mesenteric and gastroduodenal veins.  The [[Foetal Circulation - Anatomy & Physiology|ductus venosus]], a component of the foetal circulation that directs blood from the umbilical vein to the vena cava, is also part of the vitelline system.  If a functional blood vessel (ductus venosus or otherwise) connects the vitelline and cardinal systems after birth, a PSS develops.  However, in the normal animal, there are numerous non-functional connections between the two systems that may open if the pressure in the portal vein rises, leading to the formation of multiple extrahepatic acquired shunts in disease that cause portal hypertension.  Although most congenital shunts run from the portal vein to the vena cava, their embryological origin explains why shunts may also run from the splenic or gastroduodenal veins to the vena cava or azygos vein.

'''Portosystemic shunts (PSS)''' are anomalous vascular connections between the portal and systemic venous systems.  These vessels shunt blood from the '''hepatic portal vein''' (deriving from the [[Alimentary - Anatomy & Physiology #Stomach|stomach]], [[Alimentary - Anatomy & Physiology #Small Intestine|intestines]], [[Pancreas - Anatomy & Physiology|pancreas]] and [[Spleen - Anatomy & Physiology|spleen]]) directly into '''systemic venous system''', bypassing the [[Liver - Anatomy & Physiology|liver]].

Congenital shunts represent approximately 70% of the total number diagnosed in dogs and constitute the majority of those diagnosed in cats.  Congenital shunts usually involve a single (or occasionally double) anomalous vessel which may be located outside of the hepatic parenchyma (extrahepatic) or within it (intrahepatic).  Extrahepatic shunts accounts for 63% of single shunts in the dog and they are most commonly found in miniature and toy breeds.  Intrahepatic shunts are often located within the left lobes of the liver and occur due to persistence of the foetal [[Foetal Circulation - Anatomy & Physiology|ductus venosus]]<ref>White RN, Burton CA. '''Anatomy of the patent ductus venosus in the dog.''' ''Vet Rec. 2000 Apr 8;146(15):425-9.''</ref>.  This form of shunt is most common in large breed dogs and patent ductus venosus is an inherited condition in Irish wolfhounds.  Intrahepatic shunts running through the central or right liver lobes are recognised and these may have a different embryological origin.

 

Congenital shunts represent approximately 70% of the total number diagnosed in dogs and constitute the majority of those diagnosed in cats.  Congenital shunts usually involve a single (or occasionally double) anomalous vessel which may be located outside of the hepatic parenchyma (extrahepatic) or within it (intrahepatic).  Extrahepatic shunts accounts for 63% of single shunts in the dog and they are most commonly found in miniature and toy breeds.  Intrahepatic shunts are often located within the left lobes of the liver and occur due to persistence of the foetal [[Foetal Circulation - Anatomy & Physiology|ductus venosus]].  This form of shunt is most common in large breed dogs and patent ductus venosus is an inherited condition in Irish wolfhounds.  Intrahepatic shunts running through the central or right liver lobes are recognised and these may have a different embryological origin.

Acquired shunts represent approximately 20% of those diagnosed in dogs and they often consist of multiple small vessels.  They arise due to portal hypertension, following an increased resistance to portal blood flow.  The increased pressure in the portal vein and its tributaries causes numerous non-functional microvascular communications with the systemic venous system to open.  The causes of portal hypertension are numerous and they may be divided into pre-hepatic, hepatic and post-hepatic:

Acquired shunts represent approximately 20% of those diagnosed in dogs and they often consist of multiple small vessels.  They arise due to portal hypertension, following an increased resistance to portal blood flow.  The increased pressure in the portal vein and its tributaries causes numerous non-functional microvascular communications with the systemic venous system to open.  The causes of portal hypertension are numerous and they may be divided into pre-hepatic, hepatic and post-hepatic:

**'''[[Thrombosis|Thrombosis of the portal vein]]''', '''hepatic arteriovenous fistulae''' and '''congenital hypoplasia of the portal vein.'''

**'''[[Thrombosis|Thrombosis of the portal vein]]''', '''hepatic arteriovenous fistulae''' and '''congenital hypoplasia of the portal vein.'''

The pathophysiology of PSS relates to the shunting of portal blood directly from the systemic circulation, resulting in hyperammonaemia and [[Hepatic Encephalopathy|hepatic encepalopathy]].  Animals with PSS also have reduced function of the hepatic component of the monocyte phagcoyte system (chiefly the Kupffer cells) and they often develop bacteraemia.  Gram negative bacteria deriving from the GI tract are involved most commonly.

The pathophysiology of PSS relates to the shunting of portal blood directly into the systemic circulation, resulting in hyperammonaemia and [[Hepatic Encephalopathy|hepatic encephalopathy]].  Animals with PSS also have reduced function of the hepatic component of the monocyte phagocyte system (chiefly the Kupffer cells) and they often develop bacteraemia.  Gram negative bacteria deriving from the GI tract are involved most commonly.  This phenomenon may be of greater importance with acquired PSS <ref>Tobias KM, Besser TE. '''Evaluation of leukocytosis, bacteremia, and portal vein partial oxygen tension in clinically normal dogs and dogs with portosystemic shunts.''' ''J Am Vet Med Assoc. 1997 Sep 15;211(6):715-8.''</ref><ref>Howe LM, Boothe DM, Boothe HW. '''Detection of portal and systemic bacteremia in dogs with severe induced hepatic disease and multiple portosystemic shunts.''' ''Am J Vet Res. 1999 Feb;60(2):181-5.''</ref>.

==Signalment==

==Signalment==

Congenital portosystemic shunts are diagnosed regularly in dogs under one year of age, although they may be ten years old or more at presentation.  Extrahepatic shunts occur most commonly in dogs of the small or toy breeds, including Shih tzus, West Higland white terriers, Maltese terriers and Yorkshire terriers.  Intrahepatic shunts are much less common and occur in larger breeds such as Irish wolfhounds (in which patent ductus venosus is thought to be inherited), golden retrievers and Australian cattle dogs.  The condition occurs occasionally in cats, horses, cows and pigs.

Congenital portosystemic shunts are diagnosed regularly in dogs under one year of age, although they may be ten years old or more at presentation.  Extrahepatic shunts occur most commonly in dogs of the small or toy breeds, including Shih tzus, West Higland white terriers, Maltese terriers and Yorkshire terriers.  Intrahepatic shunts are much less common and occur in larger breeds such as Irish wolfhounds (in which patent ductus venosus is thought to be inherited<ref>van Steenbeek FG, Leegwater PA, van Sluijs FJ, Heuven HC, Rothuizen J. '''Evidence of inheritance of intrahepatic portosystemic shunts in Irish Wolfhounds.''' ''J Vet Intern Med. 2009 Jul-Aug;23(4):950-2. Epub 2009 May 30.''</ref>), golden retrievers and Australian cattle dogs<ref>Hunt GB. '''Effect of breed on anatomy of portosystemic shunts resulting from congenital diseases in dogs and cats: a review of 242 cases.''' ''Aust Vet J. 2004 Dec;82(12):746-9.''</ref>.  The condition occurs occasionally in cats, horses, cows and pigs.

Acquired shunts occur in animals with portal hypertension, of which the most common causes are [[Hepatitis, Chronic|chronic hepatitis]] in dogs and cholangitis in cats.  

Acquired shunts occur in animals with portal hypertension, of which the most common causes are [[Hepatitis, Chronic|chronic hepatitis]] in dogs and cholangitis in cats.  

==Diagnosis==

==Diagnosis==

===Clinical Signs===

===Clinical Signs===

All portosystemic shunts are likely to cause [[Hepatic Encephalopathy|hepatic encephalopathy]](HE) and PSS is the major cause of this disease. HE mainly causes waxing and waning neurological signs, including central blindness, seizures, depression and bizarre behaviour.  Cats often show hypersalivation/ptyalism.

All portosystemic shunts are likely to cause [[Hepatic Encephalopathy|hepatic encephalopathy]](HE) and PSS is the major cause of this disease. HE mainly causes waxing and waning neurological signs, including central blindness, seizures, depression and bizarre behaviour.  Cats often show hypersalivation/ptyalism.

In additon, animals with congenital PSS may show the following signs:

In additon, animals with congenital PSS may show the following signs:

*'''Urinary tract signs''', including dysuria, stranguria, haematuria and pollakiuria.  These signs occur because an increased blood ammonia concentration decreases the ability of enzymes to convert [[Urate Metabolism - Pathology|uric acid]] to allantoin, resulting in urate urolithiasis and urethral obstruction.  Ammonium biurate are the most common uroliths to be formed.

*'''Urinary tract signs''', including dysuria, stranguria, haematuria and pollakiuria.  These signs occur because an increased blood ammonia concentration decreases the ability of enzymes to convert [[Urate Metabolism - Pathology|uric acid]] to allantoin, resulting in urate urolithiasis and urethral obstruction.  Ammonium biurate are the most common uroliths to be formed.

*'''Polyuria and polydipsia''' occur for reasons that are not fully understood.  Urea synthesis is reduced in animals with PSS (because ammonia is not taken up by the liver in the normal way) and a reduction in the urea concentration of the renal medulla reduces the ability of the kidney to concentrate urine.  The hypofunctional liver probably also degrades cortisol at a reduced rate, increasing the circulating concentration of this diuretic hormone.   

*'''Polyuria and polydipsia''' occur for reasons that are not fully understood.  Urea synthesis is reduced in animals with PSS (because ammonia is not taken up by the liver in the normal way) and a reduction in the urea concentration of the renal medulla reduces the ability of the kidney to concentrate urine.  The hypofunctional liver probably also degrades cortisol at a reduced rate, increasing the circulating concentration of this diuretic hormone.   

*Intermittent '''gastro-intestinal signs''' such as [[Stomach and Abomasum Consequences of Gastric Disease - Pathology|vomiting]] and [[Diarrhoea|diarrhoea]].

*Intermittent '''gastro-intestinal signs''' such as [[Vomiting|vomiting]] and [[Diarrhoea|diarrhoea]].

*'''Ascites''' may occur due to [[Hypoalbuminaemia|hypoalbuminaemia]].

*'''Ascites''' may occur due to [[Hypoalbuminaemia|hypoalbuminaemia]].

*'''Bleeding tendencies''' due to coagulopathy, but this condition is often subclinical.

*'''Bleeding tendencies''' due to coagulopathy, but this condition is often subclinical.

===Laboratory Tests===

===Laboratory Tests===

====Haematology====

====Haematology====

Animals with congenital PSS often have '''microcytic normochromic red blood cells''' due to sequestration of iron.  '''Leucocytosis''' may occur as a response to bacteraemia due to a reduction hepatic phagocytic activity.

Animals with congenital PSS often have '''microcytic normochromic red blood cells''' due to sequestration of iron <ref>Simpson KW, Meyer DJ, Boswood A, White RN, Maskell IE. '''Iron status and erythrocyte volume in dogs with congenital portosystemic vascular anomalies.''' ''J Vet Intern Med. 1997 Jan-Feb;11(1):14-9.''</ref>.  '''Leucocytosis''' may occur as a response to bacteraemia due to a reduction in hepatic phagocytic activity.

Animals with inflammatory liver disease may have '''leucocytosis''' of various types and may have '''acanthocytic''' red blood cells.

Animals with inflammatory liver disease may have '''leucocytosis''' of various types and may have '''acanthocytic''' red blood cells.

====Other Tests====

====Other Tests====

*'''Increased postprandial ± preprandial [[Liver - Anatomy & Physiology #Bile Acids|bile acid]]''' concentrations.  Bile acids are normally removed from the portal blood by the liver but, in an animal with PSS, they enter the systemic venous system directly.  If the preprandial level is elevated beyond ~100 umol/l, a bile acid stimulation test will not achieve any higher sensitivity for the detection of PSS.  A bile acid stimulation test is performed by measuring preprandial bile acids, feeding the animal and measureing post prandial bile acids two hours later.  The preprandial sample may occasionally be higher than the postprandial if a gall bladder contraction occurred just before the first sample was taken.

*'''Increased postprandial ± preprandial [[Liver - Anatomy & Physiology #Bile Acids|bile acid]]''' concentrations.  Bile acids are normally removed from the portal blood by the liver but, in an animal with PSS, they enter the systemic venous system directly.  If the preprandial level is elevated beyond ~100 umol/l, a bile acid stimulation test will not achieve any higher sensitivity for the detection of PSS.  A bile acid stimulation test is performed by measuring preprandial bile acids, feeding the animal and measureing post prandial bile acids two hours later.  The preprandial sample may occasionally be higher than the postprandial if a gall bladder contraction occurred just before the first sample was taken.  Measurement of serum bile acid concentration has a sensitivity of >90% for the detection of congenital portosystemic shunts but its specificity is much lower than that of an ammonia tolerance test because it may be elevated in many other types of liver disease <ref name="one">Gerritzen-Bruning MJ, van den Ingh TS, Rothuizen J. '''Diagnostic value of fasting plasma ammonia and bile acid concentrations in the identification of portosystemic shunting in dogs.''' ''J Vet Intern Med. 2006 Jan-Feb;20(1):13-9.''</ref>.

*'''Increased blood ammonia concentration''' is diagnostic of PSS for the same reasons as are elevated bile acids.  An ammonia tolerance test can be performed by administering ammonium chloride (or a small meal) to a fasted animal and measuring the change in blood ammonia level.  Samples must be frozen immediately after collection as continued red blood cell metabolism will artificially raise ammonia levels in stored samples.

*'''Increased blood ammonia concentration''' is diagnostic of PSS for the same reasons as are elevated bile acids.  An ammonia tolerance test can be performed by administering ammonium chloride (or a small meal) to a fasted animal and measuring the change in blood ammonia level.  Samples must be frozen immediately after collection as continued red blood cell metabolism will artificially raise ammonia levels in stored samples.  Elevated fasting ammonia concentration is reported to have a sensitivity of 100% for the detection of congenital portosystemic shunts <ref name="one">nothing</ref>.

*'''Reduced serum iron concentration''' due to sequestration.

*'''Reduced serum iron concentration''' due to sequestration.

*'''Clotting times''' can be measured in animals where a coagulopathy is suspected.

*'''Clotting times''' can be measured in animals where a coagulopathy is suspected.

====Radiography====

====Radiography====

A definitive diagnosis relies on visualisation of the shunting blood vessel but radiography may reveal changes that are supportive of a diagnosis of PSS:

A definitive diagnosis relies on visualisation of the shunting blood vessel but radiography may reveal changes that are supportive of a diagnosis of PSS:

*'''Renomegaly''' is thought to occur as the kidneys attempt to remove and metabolise ammonia

*'''Renomegaly''' is thought to occur as the kidneys attempt to remove and metabolise ammonia.

*'''Microhepatica''' probably occurs because the liver is deprived of growth factors from the pancreas and other abdominal organs which are usually carried to it in the portal blood, for example the somatomedins (insulin-like growth factors, IGFs).

*'''Microhepatica''' probably occurs because the liver is deprived of growth factors from the pancreas and other abdominal organs which are usually carried to it in the portal blood, for example the somatomedins (insulin-like growth factors, IGFs).

*'''Urate uroliths''' are '''radiolucent''' and will not be detected by radiographs.

*'''Urate uroliths''' are '''radiolucent''' and will not be detected by radiographs.

====Ultrasonography====

====Ultrasonography====

The shunting vessel may be identified by ultrasound scan, especially if a '''colour flow Doppler''' facility is available.  Congenital shunts are usually thin-walled, tortuous vessels with '''turbulent flow''' and it should be noted that they may run between the tributaries of the portal vein and the azygos vein, rather than the portal vein itself.  Acquired shunting vessels can often be located around the cranial pole of the left kidney.  It may require some skill to find a shunting vessel.   

The shunting vessel may be identified by ultrasound scan<ref>d'Anjou MA, Penninck D, Cornejo L, Pibarot P. '''Ultrasonographic diagnosis of portosystemic shunting in dogs and cats.''' ''Vet Radiol Ultrasound. 2004 Sep-Oct;45(5):424-37.''</ref>, especially if a '''colour flow Doppler''' facility is available.  Congenital shunts are usually thin-walled, tortuous vessels with '''turbulent flow''' and it should be noted that they may run between the tributaries of the portal vein and the azygos vein, rather than the portal vein itself.  Acquired shunting vessels can often be located around the cranial pole of the left kidney.  It may require some skill to find a shunting vessel.   

Scans of the urinary bladder and urethra may reveal the presence of '''urate uroliths''' and '''thickening of the bladder wall''' due to cystitis.

Scans of the urinary bladder and urethra may reveal the presence of '''urate uroliths''' and '''thickening of the bladder wall''' due to cystitis.

==Treatment==

==Treatment==

In animals with acquired PSS, the underlying cause should be treated and HE should be managed as described [[Hepatic Encephaolopathy|here]]. Acquired shunts should never be ligated as they occur as a compensatory response to portal hypertension and ligation would increase portal pressure.

In animals with acquired PSS, the underlying cause should be treated and [[Hepatic Encephalopathy|hepatic encephalopathy should be managed]]. '''Acquired shunts should never be ligated''' as they occur as a compensatory response to portal hypertension and ligation would increase portal pressure.

Animals affected by congenital PSS may be managed either medically or surgically but a recent study has shown that those undergoing surgical ligation of the shunting vessel have a longer median survival time.  Medical management is often employed in those animals that show few clinical signs on presentations, are older or which have a shunt that is not amenable to ligation.   

Animals affected by congenital PSS may be managed either medically or surgically but a recent study has shown that those undergoing surgical ligation of the shunting vessel have a longer median survival time<ref>Greenhalgh SN, Dunning MD, McKinley TJ, Goodfellow MR, Kelman KR, Freitag T, O'Neill EJ, Hall EJ, Watson PJ, Jeffery ND '''Comparison of survival after surgical or medical treatment in dogs with a congenital portosystemic shunt.''' ''J Am Vet Med Assoc. 2010 Jun 1;236(11):1215-20.''</ref>.  Medical management is often employed in those animals that show few clinical signs on presentations, are older or which have a shunt that is not amenable to ligation.   

===Medical Management===

===Medical Management===

A suitable regime would incorporate the following features:

A suitable regime would incorporate the following features:

*A '''diet''' with '''protein of high quality''' and with both soluble and insoluble fibre.  Severe protein restriction is only necessary in animals showing signs of HE and it is otherwise detrimental because animals with PSS are often hypoalbuminaemic.  A protein of high quality is selected so that excess amino acids are not available to colonic bacteria and suitable sources would be cottage cheese in dogs or white fish in cats.  Soluble fibre acts in a similar manner to lactulose (below) whereas insoluble fibre decreases intestinal transit time and helps to prevent constipation.

*A '''diet''' with '''protein of high quality''' and with both soluble and insoluble fibre.  Severe protein restriction is only necessary in animals showing signs of HE and it is otherwise detrimental because animals with PSS are often hypoalbuminaemic.  A protein of high quality is selected so that excess amino acids are not available to colonic bacteria and suitable sources include cottage cheese in dogs or white fish in cats.  Soluble fibre acts in a similar manner to lactulose (below) whereas insoluble fibre decreases intestinal transit time and helps to prevent constipation.

*'''Lactulose''', a synthetic disaccharide that causes acidification of the colonic environment when it is fermented by bacteria. This environment promotes the conversion of ammonia to ammonium and the latter ions are not easily absorbed due to their electrical charge.  The trapped ammonia is therefore excreted in faeces. Lactulose is also an osmotic laxative that reduces the amount of time available for colonic bacteria to act on surplus amino acids.

*'''[[Lactulose]]''', a synthetic disaccharide that causes acidification of the colonic environment when it is fermented by bacteria. This environment promotes the conversion of ammonia to ammonium and the latter ions are not easily absorbed due to their electrical charge.  The trapped ammonia is therefore excreted in faeces. Lactulose is also a cathartic laxative that reduces the amount of time available for colonic bacteria to act on surplus amino acids.

*Administration of '''oral antibiotics''' to reduce the numbers of colonic bacteria.  Neomycin, ampicillin or metronidazole are commonly used for this purpose.

*Administration of '''oral antibiotics''' to reduce the numbers of colonic bacteria.  Neomycin, ampicillin or metronidazole are commonly used for this purpose.

=====Extrahepatic Shunts=====

=====Extrahepatic Shunts=====

A ventral midline coeliotomy is performed and the shunting vessel is identified.  If pre-operative imaging revealed the location of the shunt, it should be found easily but intra-operative mesenteric portovenography can be performed by catheterising a jejunal vein and instilling contrast medium.  As a guide, the vena cava accepts blood from the renal veins and the small phrenico-abdominal veins before it reaches the hepatic hilus.  Any vessel that joins the vena cava bewteen the phrenico-abdominal and hepatic veins is abnormal.

A ventral midline coeliotomy is performed and the shunting vessel is identified.  If pre-operative imaging revealed the location of the shunt, it should be found easily but intra-operative mesenteric portovenography can be performed by catheterising a jejunal vein and instilling contrast medium.  As a guide, the vena cava accepts blood from the renal veins and the small phrenico-abdominal veins before it reaches the hepatic hilus.  Any vessel that joins the vena cava between the phrenico-abdominal and hepatic veins is abnormal.

Direct ligation of the shunt will cause a large rise in portal pressure, reducing the venous drainage of the organs contributing to the portal vein.  For this reason, a tributary to the portal vein (such as a jejunal vein) should be catheterised to allow the portal pressure to be measured directly during the procedure.  When the shunt is ligated, the portal pressure should not rise by more than 10 cm of water from its baseline value and it should not rise above an absolute value of 20-23 cm of water.  If the portal pressure rises above this level, the surgeon is likely to notice that the intestines are blanched (due to reduced perfusion), that the pulses in the mesenteric arteries are hyperkinetic, that the intestines show vigorous contractility and that the pancreas appears oedematous.  If any of these signs are observed, the shunt should be attenuated rather than completely ligated.

Direct ligation of the shunt will cause a large rise in portal pressure, reducing the venous drainage and perfusion of the organs draining into the portal vein.  For this reason, a tributary to the portal vein (such as a jejunal vein) should be catheterised to allow the portal pressure to be measured directly during the procedure.  When the shunt is ligated, the portal pressure should not rise by more than 10 cm of water from its baseline value and it should not rise above an absolute value of '''20-23 cm of water'''.  If the portal pressure rises above this level, the surgeon is likely to notice that the '''intestines are blanched''' (due to reduced perfusion), that the '''pulses in the mesenteric arteries are hyperkinetic''', that the '''intestines show vigorous contractility''' and that the '''pancreas appears oedematous'''.  If any of these signs are observed, the shunt should be attenuated rather than completely ligated.

For complete ligation, silk is often used as a suture material in dogs because its presence promotes a fibrous reactions which reinforces the ligature.  Although silk is often categorised as a non-absorbable suture material, its strength is lost after 6 months and it is often fully absorbed after approximately 2 years.  Better knot security can be achieved if the silk is wet when the ligatures are tied.  Since silk does not stimulate a strong inflammatory response in cats, it is preferable to use the synthetic non-absorbable monofilament polypropylene in this species.

For complete ligation, silk is often used as a suture material in dogs because its presence promotes a fibrous reactions which reinforces the ligature.  Although silk is often categorised as a non-absorbable suture material, its strength is lost after 6 months and it is often fully absorbed after approximately 2 years.  Better knot security can be achieved if the silk is wet when the ligatures are tied.  Since silk does not stimulate a strong inflammatory response in cats, it is preferable to use the synthetic non-absorbable monofilament polypropylene in this species.

If the shunt cannot be ligated, attenuation may be achieved by three major techniques:

If the shunt cannot be ligated, attenuation may be achieved by three major techniques:

*An '''ameroid constrictor''' consists of a ring of stainless steel with an collar of casein.  When the ring is applied around a vessel, the casein sheath swells gradually to occlude blood flow and it may also stimulate some fibrosis.     

*An '''ameroid constrictor''' consists of a ring of stainless steel with an inner collar of casein.  When the ring is applied around a vessel, the casein sheath swells gradually to occlude blood flow and it may also stimulate some fibrosis.  Placement of an ameroid constrictor also results in a much shorter surgical time than complete ligation <ref>Hurn SD, Edwards GA. '''Perioperative outcomes after three different single extrahepatic portosystemic shunt attenuation techniques in dogs: partial ligation, complete ligation and ameroid constrictor placement.''' ''Aust Vet J. 2003 Nov;81(11):666-70.''</ref>.     

*'''Cellophane banding''' involves the application of cellophane around the shunt. This material is sutured in place to stimulate fibrosis around the vessel, resulting in gradual occlusion. This material does not stimulate a strong inflammatory response in cats and should not be used in this species.

*'''Cellophane banding''' involves the application of cellophane around the shunt. Real cellophane is made from regenerated cellulose. <ref>Smith et al [http://www.ncbi.nlm.nih.gov/pubmed/23550728] </ref>evaluated commonly used sources of cellophane and determined that only one was cellulose based and not a plastic. This may be why historical outcomes of cellophane banding for attenuation of portosystemic shunts has been variable, especially in cats. Cellophane has reportedly variable outcomes in cats, and some surgeons will prefer it not be used in this species, however recent literature suggests that good outcomes can still be achieved<ref>[http://www.ncbi.nlm.nih.gov/pubmed/21194327]</ref>.Cellophane made from cellulose is a foreign material and is passed around the shunting vessel and secured in place to stimulate fibrosis, resulting in gradual occlusion. There is now a commercial supplier of cellophane for veterinary use<ref>[https://www.cellovet.com]</ref>.

*'''Partial ligation''' is achieved by applying a loose ligature to the shunt so that some blood flow still occurs.  In a proportion of animals, a complete ligation will then have to be performed at a later date.

*'''Partial ligation''' is achieved by applying a loose ligature to the shunt so that some blood flow still occurs.  In a proportion of animals, a complete ligation will then have to be performed at a later date.

*'''Portal hypertension''', causing ascites, haemorrhagic diarrhoea, septic shock and a painful abdomen.  The abdominal girth is often measured regularly after the surgical procedure to assess the degree of abdominal distension.  Some ascites is to be expected but severe clinical signs warrant a further surgical procedure to loosen the ligature around the shunt.  Ascites should resolve over time but it can be managed with the diuretic spironolactone (because it occurs in part due to inappropriate activation of the renin-angiotensin-aldosterone system).

*'''Portal hypertension''', causing ascites, haemorrhagic diarrhoea, septic shock and a painful abdomen.  The abdominal girth is often measured regularly after the surgical procedure to assess the degree of abdominal distension.  Some ascites is to be expected but severe clinical signs warrant a further surgical procedure to loosen the ligature around the shunt.  Ascites should resolve over time but it can be managed with the diuretic spironolactone (because it occurs in part due to inappropriate activation of the renin-angiotensin-aldosterone system).

*'''Portal vein thrombosis''' because portal blood flow may be drastically reduced.

*'''Portal vein thrombosis''' because portal blood flow may be drastically reduced.

*'''Seizures''' or '''status epilepticus''', particularly in small breeds of dog.  Seizures occur most commonly 1-3 days after ligation and probably result from rebalancing of neurotransmitter levels in the CNS.  Long-term anticonvulsant therapy may be required and some animals may acquire permanent defects, such as blindness.  

*'''Seizures''' or '''status epilepticus''', particularly in small breeds of dog.  Seizures occur most commonly 1-3 days after ligation and probably result from rebalancing of neurotransmitter levels in the CNS.  Long-term anticonvulsant therapy may be required and some animals may acquire permanent defects, such as blindness.

==Prognosis==

==Prognosis==

The prognosis for outcome depends on the age of presentation and the urea concentration at presentation, with older dogs with higher levels of urea having better outcomes.  Dogs usually respond very well to total surgical ligation if they do not experience severe adverse effects in the week following the procedure but the response in cats is less favourable.

The prognosis for outcome depends on the age of presentation and the urea concentration at presentation, with older dogs with higher levels of urea having better outcomes.  Dogs usually respond very well to total surgical ligation if they do not experience severe adverse effects in the week following the procedure but the response in cats is less favourable.

==References==

==References==

*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''.

*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''.

*Fossum, T. W. et. al. (2007) '''Small Animal Surgery (Third Edition)''' ''Mosby Elsevier''.

*Fossum, T. W. et. al. (2007) '''Small Animal Surgery (Third Edition)''' ''Mosby Elsevier''.

*Nelson, R.W. and Couto, C.G. (2009) '''Small Animal Internal Medicine (Fourth Edition)''' ''Mosby Elsevier''.

*Nelson, R.W. and Couto, C.G. (2009) '''Small Animal Internal Medicine (Fourth Edition)''' ''Mosby Elsevier''.

*Watson, P. (1997) '''Decision making in the management of portosystemic shunts''' ''In Practice'' 19;106 - 120 [http://inpractice.bvapublications.com/cgi/reprint/19/3/106?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=portosystemic+shunt&searchid=1&FIRSTINDEX=0&sortspec=relevance&resourcetype=HWCIT]

* [http://inpractice.bvapublications.com/cgi/reprint/19/3/106?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=portosystemic+shunt&searchid=1&FIRSTINDEX=0&sortspec=relevance&resourcetype=HWCIT Watson, P. (1997) '''Decision making in the management of portosystemic shunts''' ''In Practice'' 19;106 - 120]

[[Category:Liver_-_Developmental_Pathology]]

[[Category:Liver_-_Developmental_Pathology]]

[[Category:Liver_-_Circulatory_Disturbances]]

[[Category:Liver_-_Circulatory_Disturbances]]

 

[[Category:To_Do_-_James]]

[[Category:Expert_Review - Small Animal]]

[[Category:Cardiology Section]]