Liver Shunt Update
Dr. Karen Tobias
Shunt Management Team
For the UTmost Care
22 February 2008
Congenital portal hypoplasia (CPH), which is also known as hepatic microvascular dysplasia (MVD or HMD) is much more common than congenital portosystemic shunts (PSS) Many dogs have congenital portal hypoplasia and no clinical signs at all; owners only find out when they have bile acids checked. We tested bile acids on 139 healthy Yorkies; about 2/3's of them had bile acids over 25 and no clinical signs. These dogs may have had other liver conditions, but CPH/MVD was probably the most likely cause. Obviously, many of these dogs are living normal lives (since no one even knew they had liver problems), and most are still on a regular dog food. Dogs with bile acids less than 25 can have CPH/MVD or congenital PSS; one paper from Auburn reported 6 dogs with CPSS that had bile acids less than 25. We recently biopsied the liver of a healthy 6month old Yorkie with bile acids of 13 fasting and 9 fed (our normals are<10 and <15), and a 10 month old Yorkie with fed bile acids of 1, and both had CPH/MVD. That means that normal bile acids will not rule out the presence of this disease. Since CPH/MVD and both hereditary, dogs with high bile acids should not be bred. Unfortunately, since dogs can have CPH/MVD and normal bile acids, we will still be missing some of the carriers. Hopefully a genetic test will be coming soon from Dr. Center's lab.
As an aside, the reason the condition is now being called Congenital portal hypoplasia is because there are several diseases, including congenital portosystemic shunts, that have "hepatic microvascular dysplasia" on liver biopsies. A liver biopsy alone cannot differentiate between CPH/HMD and congenital PSS. We usually take liver biopsies from multiple lobes; right now I don't know of any published papers that show a difference between liver lobes, but it's safest to take more than one sample.
In dogs with CPH/MVD, bile acids can change from day to day. Bile acids are affected by how fast things pass through the intestines and how well the intestines are absorbing them at any given time. Therefore, we can't use bile acids to monitor how well a dog with CPH/MVD is doing.
Rectal scintigraphy has been used for several decades to diagnose shunting. A newer technique is "splenic" scintigraphy, where the radioactive material is injected directly into the spleen instead of being given by enema. This technique was developed at UTCVM; many radiologists are switching to this procedure because it uses less radioactive material, provides a faster study, allows the animals to clear radioactivity faster, and provides better images than rectal scintigraphy.
Of dogs with congenital
portosystemic shunts, one third can live long, relatively healthy lives with
proper medical management. These are usually the dogs that are older at
the time of diagnosis, have no neurologic problems, and have relatively normal
bloodwork (albumin, protein, and blood urea nitrogen concentrations). We
cannot predict which animals will do well without surgery. The other dogs
that should not have surgical repair are those that are missing a portal vein
(less than 1% of our patients). Often times, this cannot be determined
before surgery with very expensive tests such as CAT scans or MRI.
Our survival rate from surgery is 99%; those that die usually have other illnesses so they would not have normal lifespans. We use ameroid constrictors to close the shunts slowly; cellophane bands can also be used successfully. The death rate is higher when sutures are used to partially or completely close off the shunt.
The only way to find out if
increased bile acids (any increase) is significant is to do a liver biopsy.
So far, the few dogs that we've biopsied with bile acids over 25 have all had
abnormal livers. Dr. Sura and I are going to put together a study where we
will be offering free liver biopsies for any Yorkie spay or castration (we do a
mini approach, similar to laparoscopy but
faster). Hopefully this will provide a published study that confirms what most of us feel is true.
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