Changes

==Description==

==Description==

'''Portsystemic shunts (PSS)''' are anomalous vessels vascular connections between the portal and systemic venous systems.  This allows for some portal blood draining from the stomach, intestines, pancreas and spleen to bypass the liver and drains directly into the systemic circulation.  PSS may be congenital or acquired secondary to portal hypertension.

'''Portosystemic shunts (PSS)''' are anomalous vascular connections between the portal and systemic venous systems.  This allows for some portal blood draining from the stomach, intestines, pancreas and spleen to bypass the liver and drains directly into the systemic circulation.  PSS may be congenital or acquired secondary to portal hypertension.

Congenital PSS occurs in approximately 70% of PSS in dogs and majority of PSS in cats.  It commonly present as a single, or at most double, extrahepatic or intrahepatic anomolous vessel.  Extrahepatic PSS accounts for 63% of single shunts in dog and is more commonly found in miniature and toy-breed dogs.  Intrahepatic shunts are usually left-sided and result from persistent foetal ductus venosus and is more common in large breed dogs.  Right-sided or central intrahepatic shunts are recognised and these may have a different embryological origin.

Congenital PSS occurs in approximately 70% of PSS in dogs and majority of PSS in cats.  It commonly present as a single, or at most double, extrahepatic or intrahepatic anomalous vessel.  Extrahepatic PSS accounts for 63% of single shunts in dog and is more commonly found in miniature and toy-breed dogs.  Intrahepatic shunts are usually left-sided, resulting from persistent foetal ductus venosus, and more common in large breed dogs.  Right-sided or central intrahepatic shunts are recognised and these may have a different embryological origin.

Acquired PSS occurs in approximately 20% of PSS and often consists of multiple shunts.  They arise as a result of portal hypertension following increased resistance to portal blood flow.  This leads to opening of some of the numerous normal, non-functional microvascular communications.  Underlying causes of portal hypertension included acute fulminant hepatitis, hepatic fibrosis, hepatic neoplasia, portal vein thrombosis, hepatic arteriovenous fistulae and congenital hypoplasia of the portal vein.

Acquired PSS occurs in approximately 20% of PSS and often consists of multiple shunts.  They arise due to portal hypertension, following an increased resistance to portal blood flow.  This leads to opening of some of the numerous normal, non-functional microvascular communications.  Underlying causes of portal hypertension included acute fulminant hepatitis, hepatic fibrosis, hepatic neoplasia, portal vein thrombosis, hepatic arteriovenous fistulae and congenital hypoplasia of the portal vein.

*Ptyalism in cats

*Ptyalism in cats

*Dysuria, stranguria, haematuria, pollakiuria and urethral obstruction

*Dysuria, stranguria, haematuria, pollakiuria and urethral obstruction

**An increase in ammonium concentration in the blood decreases the ability of enzymes to convert uric acid to allantoin, therby results in urate urolithiasis.

**An increase in ammonium concentration in the blood decreases the ability of enzymes to convert uric acid to allantoin, thereby resulting in urate urolithiasis.

*Intermittent vomiting or diarrhoea

*Intermittent vomiting or diarrhoea

===Diagnostic Imaging===

===Diagnostic Imaging===

A definitive diagnosis relies on visualisation of the shunting blood vessel either with ultrasonography or contrast portography or at surgery.

A definitive diagnosis relies on visualisation of the shunting blood vessel.  This may be done with either ultrasonography or contrast portography or at surgery.

==Treatment==

==Treatment==

*Surgical ligation of the anomolous vessels

*Surgical ligation of the anomalous vessels

**Beware of possible portal hypertension post ligation.  For this reason, a partial ligation is performed initally, followed by a complete ligatio a few months later.

**Portal hypertension is possible post ligation.  For this reason, a partial ligation is performed initally, followed by a complete ligation a few months later.

*Medical treatment of [[Hepatic Encephalopathy]]

*Medical treatment of [[Hepatic Encephalopathy]]