There has been much work through the years to improve techniques for portosystemic shunt diagnosis and occlusion and to identify prognostic factors. Early on, surgeons documented death in some animals that did not tolerate complete acute shunt occlusion, and they developed different methods for slow occlusion. These methods were aimed to achieve gradual shunt occlusion, thereby giving the liver a chance to begin regenerating. As the liver developed, it was hoped that intrahepatic vascular resistance would fall, portal perfusion would increase, and the liver would thus be presented with increasing levels of trophic factors, thereby stimulating regeneration further. The shunt could then close naturally as the hepatic vascular system became able to accommodate normal portal perfusion.

Slow occlusion techniques that had been used widely for vascular occlusion in experimental animals were adapted for use in dogs and cats with congenital portosystemic shunts; these included ameroid constrictors, cellophane bands, hydraulic occluders and intravenous thrombogenic coils. Recently, complete occlusion has been revisited in appropriate patients using the Amplatzer occluder.

Despite extensive research into the condition, there are still no hard and fast rules for veterinarians to follow when trying to weigh risks against likely outcomes in each individual patient. Animals with shunts are from different breeds, different sizes and with widely different shunt anatomy and liver health before surgery. All these factors are likely to play a role in the final outcome.

Results for the newer occlusion methods have been now been reported in a number of case series. The largest case series (Table 1). Numerous other case series and case reports have also been published.

Table 1.

In general, all methods of slow occlusion are highly successful. Rates are comparable between ameroid constrictor placement and cellophane banding. However, all methods result in some patients that do not regain normal hepatic function. Up to 20% develop multiple acquired shunts when the original vessel closes faster than the liver vasculature can develop. A key factor in success after shunt surgery is the liver's ability to regenerate, either due to innate capacity, or the degree of liver damage suffered by the time the patient is presented for surgery. There is a suggestion from the literature that return to normal function is possible, but less likely, in older patients. While many patients have excellent results after surgery, some do poorly and therefore much recent attention has been paid to prognostic indicators, and what information might assist clinicians with decision-making and informing the owners.

It seems clear now that most extrahepatic shunts can be treated by one of the occlusion methods mentioned above. Intrahepatic shunts may be addressed surgically, using somewhat different techniques that should be chosen based on shunt anatomy. Perivascular dissection is successful for most left-divisional and some right divisional shunts. Intra-vascular occlusion may be required for some central divisional shunts, although a vascular dissection technique that excludes the left liver lobes may also be successful. Intravascular coiling shows promise and should be investigated further in larger series of cases.

Breed Influences on Prognosis After Surgery

It has long been known that large dogs tend to have intrahepatic shunts and small dogs tend to have extrahepatic shunts. A study from the University of Sydney showed that breed has a significant influence on shunt anatomy and outcome of surgery in dogs. Two hundred and fourteen dogs (91.4%), and all cats, had shunts amenable to attenuation. Inoperable shunts occurred in 19 dogs (8.2%). Fifty six of 61 (92%) operable shunts in large breed dogs were intrahepatic, versus 10/153 (7%) in small breeds (P < 0.0001). Breeds that were not predisposed to portosystemic shunts were significantly more likely to have unusual or inoperable shunts than dogs from predisposed breeds (29% versus 7.6%, P < 0.0001). The study concluded that animals presenting with signs of portosystemic shunting may suffer from a wide range of operable or inoperable conditions. Veterinarians should be aware that unusual or inoperable shunts are much more likely to occur in breeds that are not predisposed to congenital portosystemic shunts.

Postligation neurological disorder (PLND) has received a lot of attention in recent years. In general, dogs develop generalized motor seizures or even status epilepticus within the first 3 days after shunt attenuation. The reported incidence of postligation neurological disorder varies, but is somewhere around 5%. Steps taken in our practice to avoid PLND are premedication with 10 mg/kg phenobarbital at induction of anesthesia and administration of 5 mg/kg phenobarbital bid for the first 3 days after surgery. Blood glucose levels are monitored carefully and dogs fed the morning after surgery. Should neurological signs such as disorientation or seizures occur, incremental doses of 5 mg/kg phenobarbitone are given intravenously until a total dose of 30 mg/kg over a 24 hour period is given. Seizure activity is then controlled with a constant rate infusion of propofol while phenobarbitone levels drop. The survival rate of PLND causing status epilepticus is variable. Some dogs recover completely, while others show residual neurological deficits and partial motor seizures. Occasionally, PLND will manifest as twitching or ataxia, in which case the prognosis is generally good. Most studies show that cats are more likely to develop postligation neurological signs than dogs.

In conclusion reported negative prognostic signs include: age (> 5 years), uncommon breed, low protein, low urea, intrahepatic shunt, species (cat).

Positive prognostic signs include: urinary tract signs alone, porto-azygous shunt, large liver, good hepatic vascularity, partial (versus total) occlusion of intrahepatic shunts.

Excellent outcomes can be expected in approximately 80% of dogs with extrahepatic shunts and approximately 60% of dogs with intrahepatic shunts. Intrahepatic shunts are likely to be more costly and more often require multiple procedures due to the low chance of complete ligation, difficulty placing perivascular occlusion devices, and the suggestion that liver regeneration is less likely following surgery.

References

1.  Adin CA, et al. Outcomes associated with use of a percutaneously controlled hydraulic occluder for treatment of dogs with intrahepatic portosystemic shunts. J Am Vet Med Assoc 2006;229:1749–1755.

2.  Bussadori R, et al. Transvenous coil embolisation for the treatment of single congenital portosystemic shunts in six dogs. Vet J 2008;176:221–226.

3.  Cabassu J, Seim HB III, MacPhail CM, et al. Outcomes of cats undergoing surgical attenuation of congenital extrahepatic portosystemic shunts through cellophane banding: 9 cases (2000–2007). J Am Vet Med Assoc 2011;238:89–93.

4.  Hogan DF, et al. Intravascular occlusion for the correction of extrahepatic portosystemic shunts in dogs. J Vet Intern Med 2010;24:1048.

5.  Hunt GB, et al. Outcomes of cellophane banding for congenital portosystemic shunts in 106 dogs and 5 cats. Vet Surg 2004;33:25–31.

6.  Mehl M, et al. Evaluation of ameroid ring constrictors for treatment of single extrahepatic portosystemic shunts in dogs: 168 cases (1995–2001). J Am Vet Med Assoc 2005;226:2020–2030.