What is Microvascular Dysplasia of the Liver?

The liver performs an incredible number of functions to maintain health of animals, including filtering out toxins, storing sugar, and making proteins. Most of the blood that is carried to the liver for these processes arrives via the portal vein, which drains the intestines, stomach, pancreas, and spleen. Within the liver, the portal vein branches into smaller and smaller vessels so that the blood can percolate throughout the tissues to each liver cell. When these microscopic vessels are abnormal on liver biopsy, the condition is called “hepatic microvascular dysplasia (HMD or MVD)” or “portal atresia”. When the microscopic vessels within the liver are underdeveloped or absent, the liver becomes small (“atrophied”) and the animal can no longer process toxins or make proteins necessary for growth and normal function.

Hepatic microvascular dysplasia (HMD) or portal atresia is a histologic diagnosis, meaning it only describes the biopsy findings. In fact, there are many conditions that can cause these findings, including congenital portosystemic shunts; however, when the diagnosis is made without evidence of a congenital shunt, then the dogs are often given the diagnosis of HMD as a specific disease.

Clinical presentation of microvascular dysplasia in dogs

Dogs with HMD can present with signs similar to dogs with congenital portosystemic shunts; however, many dogs have no clinical signs at all. Often affected dogs are 3 to 4 years old before they have clinical signs. Some affected dogs are smaller than normal, with poor muscle development. They may seem less intelligent or quieter because of the toxins that depress their brains. They may have a loss of appetite or occasional bouts of vomiting and diarrhea. Some dogs may have a greater risk of infections or develop bladders stones. Severely affected dogs may be wobbly or act drunk or blind and can even seizure. Rarely, dogs will develop fluid filled bellies from liver failure.

Learn more about MVD from the surgical specialists at ACVS:

NB: I find that medical and dietary management of these patients in my practice to be very rewarding. Many MVD and portosystemic shunt patients can live normal lives. There is plenty of great info and support on the internet for the guardians of these patients.