Changes

{| cellpadding="10" cellspacing="0" border="1"

{| cellpadding="10" cellspacing="0" border="1"

| See also:

| See also:

| '''[[Portosystemic Shunt]]'''

| '''[[Portosystemic Shunt]]'''

==Description==

==Description==

Microvascular dysplasia (MD) is a congenital defect of the hepatic vasculature that results in abnormal communication between the portal and systemic venous circulation.  Unlike [[Portosystemic Shunt|portosystemic shunting]], microvascular dysplasia is not grossly evident and occurs due to vascular connections between microscopic blood vessels.  However, MD may occur in conjunction with a gross shunting vessel and it does cause clinical signs which are very similar to those observed in animals with portosystemic shunts.   

Microvascular dysplasia (MD) is a congenital defect of the hepatic vasculature that results in abnormal communication between the portal and systemic venous circulation.  Unlike [[Portosystemic Shunt|portosystemic shunting]] (PSS), microvascular dysplasia is not grossly evident and occurs due to vascular connections between microscopic blood vessels.  The defect is thought to occur at the level of the terminal portal veins.  MD may occur in conjunction with a gross shunting vessel and it does cause clinical signs which are very similar to those observed in animals with portosystemic shunts.   

==Signalment==

==Signalment==

MD occurs as a congenital disease in several small breeds of dog, particularly the Yorksire terrier and Cairn terrier.  The average age at presentation is 3 years (older than most animals presenting with congenital portosystemic shunts) and the condition is more common in female dogs than males.

MD occurs as a congenital disease in several small breeds of dog, particularly the Yorksire terrier and Cairn terrier (in which the disease inherited autosomally).  The average age at presentation is 3 years, which is older than most animals presenting with congenital portosystemic shunts and the condition is more common in female dogs than males.

==Diagnosis==

==Diagnosis==

===Clinical Signs===

===Clinical Signs===

Signs are very similar to those observed in animals with congenital portosystemic shunts, as listed [[Portosystemic Shunt|here]].  Briefly, these include:

Signs are very similar to those observed in animals with congenital portosystemic shunts, as listed [[Portosystemic Shunt|here]].  Animals with MD are often less severely affected than those with PSS and they may even by asymptomatic. Briefly, common clinical signs include:

*'''Stunted growth''' compared to littermates.

*'''Stunted growth''' compared to littermates.

*Intermittent '''gastro-intestinal signs''', including vomiting and diarrhoea.

*Intermittent '''gastro-intestinal signs''', including vomiting and diarrhoea.

*'''Urinary tract signs''' resulting from urate urolithiasis.

*'''Urinary tract signs''' resulting from urate urolithiasis.

===Laboratory Tests===

===Laboratory Tests===

Diagnosis relies on ruling out the presence of a gross shunting vessel by diagnostic imaging.  A liver biopsy is then performed and histological analysis of the sample will show a pattern identical to that of a congenital portosystemic shunt:

The results of blood tests will be similar to those obtained from animals with PSS, as described [[Portosystemic Shunt|here]].  In some cases however, raised serum bile acid concentrations may be the only abnormality detected in young animals with MD and concentrations of albumin and cholesterol are less reliable in making a diagnosis.  Microcytic red blood cells are also an uncommon finding in animals with MD.

 

*'''Arteriolarisation of central veins'''

*'''Arteriolarisation of central veins'''

*'''Smooth muscle proliferation''' (segmental) within the walls of central veins

*'''Smooth muscle proliferation''' (segmental) within the walls of central veins

*'''Dilation of periacinar vascular spaces'''

*'''Dilation of periacinar vascular spaces'''

*'''Decreased diameter of intrahepatic veins'''

*'''Decreased diameter of intrahepatic veins'''

==Treatment==

==Treatment==

'''Medical management''' should be implemented, as for [[Portosystemic Shunt|portosystemic shunts]].

'''Medical management''' should be implemented, as for [[Portosystemic Shunt|portosystemic shunts]].

[[Category:Liver_-_Developmental_Pathology]]

[[Category:Liver_-_Developmental_Pathology]]

[[Category:To_Do_-_James]]

[[Category:To_Do_-_James]]