Medical management
Before surgery can be performed your pet may need to be stabilized medically. The goal of medical management is to improve your pet’s health to a point where the risk of anesthesia and surgery is low. Medical management consists of a low protein diet and oral administration of antibiotics and lactulose. The goals are to decrease the bacterial population in the intestines and to minimize the production of toxins. Lactulose is a cathartic, which promotes the expulsion of fecal matter, as well as decreasing the bacterial load in the colon. Antibiotics help to eliminate bacteria that promote the formation of toxins. The diet should provide high-quality protein but may need to be moderately restricted in amount of protein, depending on the clinical signs for each individual animal. If seizures are a part of clinical signs, anti-seizure medication may also be used. Keppra (levetiracetam), anti-seizure medical has been possibly shown to reduce the occurrence of post-operative seizures, which is a rare but potential devastating complication.

Surgical management
The treatment of choice for a single PSS is surgical attenuation (narrowing) or full ligation (tying off) of the abnormal shunt vessel. This full ligation may be done instantaneously using suture material or intra-venous injection of an embolus of special glue material, or delayed full ligation with an ameroid constrictor, cellophane band or an intra-venous embolic coil. This surgery is technically challenging, and your primary care veterinarian may refer you and your pet to an ACVS board-certified veterinary surgeon.

If a shunt cannot be identified at surgery, an intra-operative portogram is performed (Figures 2 and 3). When the shunt is identified, pressure in the portal vein may be measured to determine if complete ligation is possible. Excessively high portal system pressure, called portal hypertension, can result in death. Acute portal hypertension results in abdominal distension, pain, bloody diarrhea, ileus (stasis of bowel with gas build-up) and endotoxic shock (shock due to bacterial toxins).

Partial ligation is performed if there is a risk of portal hypertension (occlusion pressure is too high). (Figure 4)

Partial ligation of the shunt may be done by partially enclosing the vessel with a suture ligature until pressure rise is at its acceptable limit. About half of patients using this method will go on to scar close their shunts; but about half will maintain some shunting of blood and need a second surgery months later, when the liver has adapted to its new circulation and can withstand full ligation. This method is rarely used anymore to address single extrahepatic shunts, although in intra-hepatic shunts, partial ligation or trans-venous coils can be used to address the shunting vessel.  Due to the availability of ameroid constrictors, intravenous coils and cellophane bands, partial ligation is rarely used in single extrahepatic shunts.

The ameroid constrictor (Figure 5) is made of casein in a stainless steel, “C”-shaped ring. It is placed around the shunt, and the ring is closed with a small key. 

Over the next few weeks, the casein swells and gradually occludes the shunt (Figure 6). This is considered a method of gradual occlusion. 

The vessel may also be occluded using a special cellophane band (Figure 7).  The band will incite an inflammatory response, and the vessel will slowly close down over a period of months. 

Trans-venous coiling is usually used for larger, intra-hepatic shunting vessels. This is a minimally-invasive procedure in which coils are placed in the portosystemic shunt to allow the shunt to close down progressively over time. The coils are held in place by the use of a metal or metal-alloy stent. The entire procedure is performed through a small puncture in a blood vessel in the neck region. The goal of the procedure is to help the liver be able to perform normal functions more effectively as more blood travels through the liver.