When she was 7 months old, Olive, a Portuguese Water Dog, went into a coma during her spay surgery. She was transferred to an all-night veterinary hospital, where her guardian, Hannah, wondered what could have happened – why her healthy young dog of only a few months would go into a coma during a routine surgery like spaying. Olive’s blood work revealed a problem with her enzyme levels: Olive’s liver was not functioning properly. But, after receiving fluids and care from the hospital, Olive finally came out of her coma at 5 o’clock the next morning. Thrilled that Olive was conscious, Hannah took her home to the family to recuperate. A couple of weeks passed, and with Olive on antibiotics all seemed well. Then, Olive became very lethargic. She stopped eating her food and was constantly drinking water. Hannah noticed that she was growing, but not very quickly. Olive also had started bumping into things. After a trip to the veterinarian, Hannah learned that Olive’s enzyme levels were still off. This fact, followed by copious online research about Olive’s other behaviors, led Hannah to believe that Olive had an intrahepatic shunt.
What Is a Liver Shunt?
One of the liver’s primary functions is to remove toxins from the blood. A liver shunt is an abnormal blood vessel that allows blood to bypass the liver instead of passing through it. Shunts can either be within the liver (called intrahepatic) or outside the liver (extrahepatic). They can be congenital (present at birth) or acquired secondary to chronic liver disease.
In fetuses, a shunt is always present, so that the mother’s liver can do the work of cleaning the blood of toxins – as the fetus’s liver does not yet work. Usually the shunt closes soon after birth and the newborn’s liver takes over, filtering out toxins from the blood flow.
Sometimes, however, the shunt does not close properly, and a congenital shunt is formed, allowing unfiltered, contaminated blood to reach general circulation without being filtered through the liver. Toxins can build up in the bloodstream or kidneys. In addition, under normal circumstances, food is broken down or digested in the intestines and then absorbed into the portal bloodstream, which is carried through the liver. When a shunt is present, this flow is diverted; therefore, the pet lacks the necessary materials to help him grow and to give him a ready energy source.
While extrahepatic shunts are more commonly seen in small-breed dogs such as the Yorkshire Terrier, Havanese or Maltese Terrier, intrahepatic shunts occur more frequently in large-breed dogs. They are often reported in Labrador Retrievers, Irish Wolfhounds, Australian Shepherds, Australian Cattle Dogs, Samoyeds and Old English Sheepdogs. The incidence of shunts in the general dog population is 0.18 percent; it is a 36 times higher incidence in Yorkshire Terriers.
Shunts can be seen at any age, although congenital shunts are usually diagnosed before the pet is 1 or 2. Some common clinical signs of a shunt include the following:
- Intermittent anorexia
- Abnormal behavior after eating
- Neurologic dysfunction such as head-pressing, circling, pacing or unresponsiveness
- Episodes of apparent blindness
- Excessive salivation
- Pica (eating foreign material)
- Poor weight gain
- Small stature, stunted growth, poor muscle development
- Excessive sleeping, lethargy
- Excessive water consumption, excessive urination
- Straining to urinate due to bladder stone formation
- Poor recovery after surgery
Through her research, Hannah identified and reached out to specialists with expertise in shunts, and eventually connected with Margo Mehl, DVM, Diplomate, American College of Veterinary Surgeons.
A number of tests can be run to evaluate a patient that might have a shunt, for example, a complete blood count (CBC), serum chemistry panel and urinalysis. Animals with shunts generally:
- Have low blood urea nitrogen (BUN) and albumin concentrations
- May be anemic
- Have red blood cells that are smaller than normal (“microcytosis”)
- May have increases in liver enzymes (AST, ALT)
- May have urine that is dilute
- May have urine that contains small, spiky crystals (“ammonium biurate”)
Another common test is the fasting (pre-prandial) and a post-feeding (post-prandial) bile acid test. Animals with intrahepatic and extrahepatic shunts usually have elevated bile acids.
Other advanced techniques such as scintigraphy (a nuclear scan that measures blood flow), ultrasound, portography (a dye study of the venous portal system), CT, MRI or exploratory surgery may be used.
Based on Olive’s clinical signs, blood work and a scintigraphy, Dr. Mehl confirmed that Olive did indeed have a portosystemic shunt. At that time, she explained to Hannah treatment options and the risks that accompany intrahepatic shunt surgery. Hannah wanted to do all that was possible to give Olive a fighting chance, regardless of costs and risks. After all, Olive was considered to be a member of the family; Hannah’s young daughter called Olive her “sister.” A CT scan was performed to confirm the location of the shunt. Olive’s CT scan showed that she had a right divisional intrahepatic shunt, and the surgery was soon scheduled.
Treatment options for animals with liver shunts include medical management and surgery. Medical management may include feeding the pet a low-protein diet to reduce the amount of toxins produced by the liver, giving the pet lactulose to reduce the amount of toxins produced and absorbed by the large intestine, and possibly giving the patient a regimen of antibiotics to decrease the amount of toxin-producing bacteria in the intestines (and treat low-grade infections if present). Note that medical management only helps manage the circulating toxins; it does not change what happens at the level of the liver. Medical management is rarely recommended as a sole treatment option, although it is good for stabilization or if the pet owner has limited resources.
Surgery for intrahepatic shunts is more difficult than that for extrahepatic shunts, because the shunt is inside the liver and therefore more difficult to visualize. The goal of the surgery is to slowly occlude (close off) the abnormal blood vessel; closing the shunt too quickly can result in fatal portal hypertension because the liver may not yet be capable of handling the entire portal blood supply. The liver often needs time to accommodate the increased blood flow. Although techniques vary, based on her own research findings Dr. Mehl generally uses a CT to confirm the location of an intrahepatic shunt and then ties off the vessel with non-absorbable suture. Per a study conducted by Dr. Mehl, dogs with ameroid rings on intrahepatic shunts had a reduced lifespan compared to ones that were ligated; therefore, she only uses the ameroid ring on extrahepatic shunts. (An ameroid constrictor is a band that will slowly swell upon contact with fluids. It will gradually close down over the shunt over four to six weeks.) Intrahepatic shunts are often very large and may sometimes require multiple surgeries for complete occlusion. Complications from surgery, while rare, can be severe. They include: portal hypertension, neurological dysfunction/seizures, bleeding and sepsis. Post-surgery care is critical.
The mortality rate in dogs with intrahepatic shunts is higher than those with extrahepatic shunts; cats have a higher mortality rate than dogs regardless of shunt type. If the shunt is completely occluded as a result of surgery, the long-term outlook for the pet is excellent – a good quality of life and normal life expectancy are likely. If the shunt is only partially closed, the outlook is more variable. Some patients require long-term medical management as described above; ongoing tests (bile acid, liver function, etc.) should be performed to evaluate the pet’s condition.
As for our friend Olive? Well, she recovered from the surgery and she’s doing great. Olive no longer has to take antibiotics or lactulose, and her liver enzyme levels are normal. From playing tug-of-war to going on walks with the family to “organizing” her toys all over the house, Olive delights Hannah’s family every minute of the day. Hannah credits Dr. Mehl’s expertise, honesty and compassion for Olive’s new lease on life.
For More Information
Because intrahepatic shunts are more difficult to find and close off than those outside the liver, surgery involving shunts inside the liver is best performed by a Board-certified veterinary surgeon with experience in this area. At SFVS, Margo Mehl, DVM, Diplomate, American College of Veterinary Surgeons, is one of a handful of surgeons in the state of California who perform the surgery. For more information or for a telephone consultation with Dr. Mehl, please contact SFVS at 415-401-9200 or visit www.sfvs.net.
Further Reading / Article Sources
- American College of Veterinary Internal Medicine (ACVIM), Portosystemic Shunts
- University of Tennessee College of Veterinary Medicine’s Portosystemic Shunts FAQ
- Michigan Veterinary Specialists, Portosystemic Shunts (including anatomy graphics)