Portosystemic Shunts & Portal Vein Hypoplasia Flashcards
(33 cards)
What is a characteristic sign of PSS? What are some other supportive signs?
head pressing following meals - food is not metabolized properly by the liver and ammonia from food is building up
- abnormal behavior - depression, disorientation, dullness, star-gazing
- wide-circling, ataxia
- appears to be blind
- poor appetite
- vomiting
- fails to gain weight
- frequent urination
What are 7 common biochemical changes associated with PSS? What else can be seen?
- hypoglycemia
- hypoalbuminemia
- hypocholesterolemia
- low BUN
- fasting hyperammonemia
- anemia
- increased bile acids
(low liver function!)
increased liver enzyme activity, ammonium biurate crystals in urine, prolonged clotting times
What are common UA findings in cases of PSS?
- low USG
- ammonium biurate crystals
How are bile acids affected by PSS?
pre (fasted) and post (2 hours following high fat meal) samples will be increased
in response to a meal the GB will contract and release BA, which are metabolized by the liver –> with PSS, BA remain in systemic circulation
How does normal portal blood flow?
- portal vein collects blood from the pancreas, small and large intestine, spleen, and stomach
- blood then does to the liver
- blood is then sent into systemic circulation
with a PSS, blood bypasses the liver into the vena cava, so no metabolism or detoxification occurs
How is ammonia usually detoxified?
- ammonia produced in the GIT
- reaches portal circulation and then the liver
- hepatocytes metabolize ammonia into urea via the urea cycle
- urea is excreted by the kidneys
What are PSS? What 5 things do they result in?
anomalous vessels in portal circulation bypass the liver into the caudal vena cava –> decreased delivery of trophic factors (insulin, glucagon) to the liver
- poor hepatic development
- decreased protein production
- altered metabolism of fats, proteins, carbs
- hepatic failure (no blood supply!)
- decreased clearance of toxins –> CNS dysfunction
What causes hepatic encephalopathy?
PSS allows ammonia to bypass the liver and reach systemic circulation and the brain without metabolism and excretion as urea
What 4 effects does ammonia and amino acids have on the brain?
- neurotransmitter synthesis and release - imbalance of inhibitory (GABA) and excitatory (glutamate) transmission
- edema
- pro-inflammatory cytokine release
- false neurotransmitter release, which block catecholamine transmission (caused by decreased removal of (aromatic) tryptophan, tyrosine, etc.)
What is the most common toxin that causes hepatic encephalopathy? What are some others?
ammonia
- aromatic amino acids
- endogenous BZDs
- false neurotransmitters
- GABA
- glutamine
- manganese
- phenol
- short chain fatty acids
- tryptophan
What signs are associated with hepatic encephalopathy?
- ataxia
- weakness
- stupor
- head pressing
- circling
- star gazing, disorientation, bizarre behavior
- seizure, coma
typically worse after meals
What are 4 precipitating factors associated with hepatic encephalopathy?
- high protein meal - increased ammonia generation
- GI hemorrhage - increased ammonia generation
- constipation - increased time for bacterial ammonia generation
- hypokalemia, alkalosis (vomiting) - H exchanged for K in cell, increased blood pH = more ammonia formed, ammonia is more permeable in these conditions
What are the 2 types of extrahepatic shunts? In what animals are they most common?
- congenital - one large shunt, common in small breeds (Yorkies, Miniature Schnauzers)
- acquired - multiple, torturous shunts produced due to portal hypertension (cirrhosis, systemic hypertension)
How do intrahepatic shunts compare to extrahepatic?
- more common in large breeds
- harder to correct and diagnose due to their presence within the liver (require coil embolization)
What is portal vein hypoplasia? In what dogs are they most commonly seen?
microscopic intrahepatic vascular shunting that is usually an incidental finding or has much less severe clinical signs and biochemical abnormalities (encephalopathy uncommon)
older Yorkies, Miniature Schnauzers, and Cairn Terriers
What are classic signs of PSS?
- hepatic encephalopathy - head pressing or other neuro signs after a meal
- GI, urinary, and neurologic disturbances
What erythrogram change is expected with PSS? Why?
nonregenerative, microcytic, normochromic
- iron sequestration or defect in iron transport due to decreased liver production of iron carrier proteins (apotransferrin)
- decreased Fe –> decreased Hb –> extra cell division occurs during RBC formation –> smaller RBCs
Why does PSS cause hypoglycemia?
decreased hepatic synthesis
- impaired gluconeogenesis
- impaired insulin clearance and decreased response to glucagon
- decreased glycogen stores
Why does PSS cause hypoalbuminemia?
decreased hepatic synthesis
Why does PSS cause hypocholesterolemia?
- decreased hepatic synthesis
- decreased urea production
What urolith is associated with PSS? Why?
ammonium biurate
- hyperammonemia from deficient urea cycle
- inappropriate uric acid metabolism where purines from the diet are metabolized into uric acid, but the uric acid is not sent to the liver for metabolism
- excessive ammonia and uric acid excretion from the kidneys
Why does PSS cause increased clotting times?
liver is responsible for producing more clotting factors and any activated factors are cleared out
- spontaneous bleeding is uncommon, most commonly seen at surgery
Why does PSS cause elevated bile acids?
- BA are usually synthesized in the liver from cholesterol and stored in the gallbladder
- cholecystokinin is release in response to high fat levels (a meal), which causes GB contraction and BA release into the duodenum
- BA are reabsorbed in the ileum, then reaches portal blood and the liver
with a PSS, BAs bypass the liver and remain in systemic circulation
What are 3 ways to confirm diagnosis of PSS?
- non-invasive imagine - AUS, nuclear imaging (nuclear scintigraphy), CT/MRI (may not be good options with high ammonia levels due to GA)
- protein C activity
- invasive imaging - portovenography
liver biopsy cannot differentiate between PSS and microvascular dysplasia
