Exam 4: Portosystemic Shunts

define a portosystemic vascular anomaly (PSVA)

• grossly apparent abnormal connection between the portal vasculature ad the systemic circulation (connecting a branch of the portal vein to the vena cava or azygous vein) that diverts blood to the systemic circulation, bypassing the liver

what are the macroscopic PSVA

• congential portosystemic shunts- intra or extrahepatic

• arterial-venous malformations

• multiple acquired portosystemic shunts

• portal vein atresia

what are microscopic PSVA

microvascular dysplasia (MVD) = primary venous hypoplasia= primary portal vein hypoplasia = primary vein hypoplasia of the portal vein

what are extrahepatic congenital PSVA

• aberrant communications between the vitelline and cardinal embryologic venous systems

• in dogs= spleno-caval, left gastro-azygous, and right gastric

what is the major form of intrahepatic PSVA

patent ductus venosus

what is the age predeliction for PSVA

• typically present within first 2 years of life

• minimally symptomatic may be diagnosed in elderly dogs
  -E- 16% >6
  -I- 3%>6

what breeds are prone to E-PSVA

• small breeds

• yorkies, shih tzu, maltese, pug, miniature schnauzer, west highland white terrier, bichon frise, border terriers, jack russel terriers, miniature and toy poodles, hhavanese, cairn terriers, silky terriers and mixes

• heritability implicated

What breeds are prone to I-PSVA

• labrador retriever, mixed breed and siberian huskies

• inheritance is implicated in irish wolfhounds

what are typical historical signs of PSVA in dogs

• small body stature, often the runt

• signs associated with hepatc encephalopathy

• pediactric hypoglycemic in toy breeds, PU/PD → small breed that is impossible to housebreak

• pyrexia, pica, vague GI signs and pain

• signs associated with ammonium biurate urolithiasis (hematuria, stranguria, urethral obstruction

what causes hepatic encephalopathy

• blood is not being processed to remove microorganisms, toxins, nutrients from intestines → come in contact th brain → neurotoxic substances make direct contact

what are the signs of hepatic encephalopathy

• may be inapparent or only manifest as mild episodic lethargy or inappetence

• ataxia, obsessive circling, head pressing, inappropriate vocalization, amaurosis (temporary loss of vision), vestibular signs, or neck pain

• vomiting, diarrhea, inappetence and dehydration can make worse

what signs of PSVA may be seen on physical if any

• small body size compared to breed standards

• large urinary bladder

• palpable kidneys

• obvious neurobehavioral signs

• young dogs with remarkable dental plaque

• abdominal effusion suggesting portal hypertension

what is the most important clinicopathologic test for PSVA

• paired bile acids

• fasting BA> post prandial BA occurs in 15% of dogs

• repetitive testing is not recommended

how can ammonia be used for PSVA

increased typically, but can be decreased and does not correlate consistently, should be an arterial sample and must be analyzed immediately

what other clinicopathologic tests can be used for PSVA

• low protein C activity

• RBC microcytosis, low tota protein, low cholesterol concentrations, urine SG <1.025

• pogs with PSVA have a high GFR that normalizes with shunt attenuation

how does protein C relate to PSVA

• <70% activity in 80% of dogs

• reflects severity of shunting

• some E have values in grey zone likely reflects small shunt index

what are the major differences in clinicopathologic tests for I-PSVA over E

• lower protein C, antithrombin, PCV, total protein, albumin and globulin

• higher cholesterol and glucose

• more prolonged APTT

what is the gold standard for imaging of PSVA

• CT angiogram

• rapidly completed with imaging contrast administered ideally with an automatic injector

• anesthesia required

• keep and eye out for renoliths and cystoliths

what are other options for PSVA imaging

• scintigraphy- yes/no

• abdominal ultrasound- 80-90% success rate with radiologist, bit other features can support diagnosis such as a small liver, renomegaly, urinary crystals/liths, focal cvc dilation

• MRI

• portogram

what is microvascular dysplasia

• abnormal intrahepatic portal microvasculature, inconsistently affects different lobes

• histologic features usually cannot diiferentiate between PSVA and MVD

what are the major differences in diagnostics for MVD

• not associated with signs of illness, HE, ammonium biurate crystalluria or uroliths

• usually have normal protein C activity

• BA are usually not as high, but this cannot be used to distinguish phenotypes

• does not cause clinicopathologic abnormalities, shorten lifespan, require dietary modification or medication

what is important to change with MVD patients

reduce dosages of drugs that have high first pass hepatic extraction

what are the kinds of portal hypertension

• central venous pressure (CVP)

• portal venous pressure (PVP)

• free hepatic vein pressure = caudal vena cava pressure

• wedged hepatic vein pressure = sinusoidal pressure

how should multiple acqquired portosystemic shunts be managed

• medical management only

• identify and treat underlying disease

• development should not be a death sentence!

how do lab values of MAPSS compare to PSVA

• higher MCV, iron indices, liver enzymes, BUN, creatitine, globulin

• no differences in urine SG or pH