Hepatic Microvascular Dysplasia

• Small intrahepatic portal vessels and portal endothelial hyperplasia which allows abnormal communication between portal and systemic circulation.
• Can develop as a separate entity or in conjunction with a portosystemic shunt.
• Can cause c/s similar to those of PSS.
• Vomiting, diarrhoea, urinary tract changes associated with ammonium biurate urolithiasis, stunted growth, prolonged recovery from anesthesia.
• Average age of presentation =3yrs.
• Mainly small dogs, esp. Yorkies
• Females>males

Histology

• • Arteriolarization 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.
  • May also see decreased diameter of intrahepatic veins.
• Can’t be accurately distinguished from PSS alone.
• Seen in older dogs than PSS
• Higher MCV, serum postprandial bile acid concentrations, serum albumin and cholesterol concentrations when PSS and HMD together, compared to HMD alone.