PORTOSYSTEMIC SHUNT IN DOGS
Aditi Sharma (BVSc. & AH)
Introduction :- A vascular anomaly where blood supply from intestine bypasses liver due to a shunt. It results in persistence of abnormal connection between the portal vascular system and systemic circulation. Normally, blood from abdominal organs is drained by portal vein into the liver where detoxification of blood occurs.
Types :- It can be intrahepatic or Extrahepatic.
Etiology and pathophysiology :- Shunts in young animals are generally congenital (they are present at birth). Congenital portosystemic shunt (PSS) develops when ductus venosus fails to collapse at birth and remains intact and open after the fetus no longer needs it or some blood vessel outside liver develops abnormally and remains open after the ductus venosus closes. Acquired PSS occurs secondary to some liver disease like hepatic arteriovenous malformations, outflow obstruction via hepatic vein/venules due to thrombosis, chronic liver disease.
Breed predisposition :- Extra-hepatic PSS mostly occur in small breeds whereas Intra hepatic PSS can occur in any breed.Breeds mostly affected are Yorkshire Terriers, Miniature Schnauzer, Irish Wolfhounds, Maltese, Labrador Retrievers , Golden Retrievers.
Clinical Signs:- Poor growth ,behavioural abnormalities , weight loss are commonly seen with congenital PSS. Neurological signs are seen due to hepatic encephalopathy which occurs because liver is no longer able to detoxify the blood from the gastrointestinal tract. Nervous signs are Swaying , seizures , head pressing , ataxia , disorientation, staring into space, circling etc. Other signs: are vomiting , diarrhoea , ataxia , polyuria/ polydipsia , stranguria , hematuria , hypersalivation etc.
Diagnosis:- 1. history and clinical signs
- Complete Blood Count (CBC) and Serum Chemistries:- mild anemia or smaller than normal red blood cells (microcytosis) , low blood urea nitrogen (BUN) and albumin.
3.Liver function tests :- increases in liver enzymes (AST, ALT) ,elevated preprandial and postprandial bile acids.
4.Urinalysis :- Urine may have ammonium biurate crystals. These appear as yellow to brown spherules with irregular projections.
5.Abdominal radiographs :-It reveals a generalized decrease in contrast because of the decrease of abdominal fat. Size of the liver is commonly reduced (atrophy) and kidneys enlarged.
6.Abdominal ultrasound can also be done.
7.Computed tomography (CT scan) :- It is the test of choice. It measures the blood flow through liver.
Treatment:- 1.Medical management :- low protein diet and oral administration of antibiotics. Lactose is also given to change ph in intestine and making its environment unfavourable for toxin producing bacterial growth.
2.Surgical management:- Surgical ligation of the shunting vessel(s). An ameroid constrictor ring is placed around the vessel. Sometimes, shunts need to be hand-ligated if breed is large for the constrictor.
Prognosis :- The prognosis is generally good if recognized early in the course of the disease.
Surgery provides the best chance for a long, healthy life in most dogs with extrahepatic shunts.
Survival rate is high after surgical procedure , if ameroid constrictor placement is performed.
Prevention :- PSS can only be prevented by not breeding affected animals and refraining from breeding the sires and dams of affected animal.
