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 an osmotic laxative, which both decreases the bacterial load in the colon and changes the large intestinal pH to reduce the ammonia produced and subsequently absorbed. Antibiotics also 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), an anti-seizure medicine, has been possibly shown to reduce the occurrence of post-operative seizures, which is a rare but potential devastating complication.
The treatment of choice for a single PSS is surgical attenuation (narrowing) with eventual closure of the abnormal shunt vessel or full ligation if deemed appropriate by your surgeon. Complete ligation should never be done instantaneously in all patients with portosystemic shunts, which could lead to life-threatening portal hypertension, seizures, and death in some patients with under-developed portal vasculature. Attenuation, or gradual closure, is a delayed full ligation with an ameroid ring constrictor, cellophane band, hydraulic occluder placement, or intravascular techniques. 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 3 and 4). When the shunt is identified, pressure in the portal vein may be measured (figure 5) 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 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 6, 7) 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 7). This is considered a method of gradual occlusion.
The vessel may also be occluded using a special cellophane band (Figure 8). 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.
At the time of shunt attenuation, your veterinarian may also recommend cystotomy if bladder stones are present.