Hepatic Microvascular Dysplasia

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 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.

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.

Diagnosis

Clinical Signs

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

• Stunted growth compared to littermates.
• Intermittent gastro-intestinal signs, including vomiting and diarrhoea.
• Urinary tract signs resulting from urate urolithiasis.
• Prolonged recovery from sedation or anaesthesia due to reduced hepatic metabolism of drugs.

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:

• Arteriolarisation of central veins
• Smooth muscle proliferation (segmental) within the walls of central veins
• Random distribution of small calibre vessels
• Endothelial hyperplasia within portal triads
• Dilation of periacinar vascular spaces
• Decreased diameter of intrahepatic veins

Blood samples

• Higher MCV, serum postprandial bile acid concentrations, serum albumin and cholesterol concentrations when PSS and HMD together, compared to HMD alone.

Treatment

Medical management should be implemented, as for portosystemic shunts.

See also: Portosystemic Shunt