Porto-systemic Vascular Anomalies

Question 1

What physiological mechanisms trigger closure of the normal fetal vasculature?

Question 2

Why does the liver fail to develop adequately in the presence of a PSVA?

Question 3

Describe the broad anatomical grouping of portosystemic vascular anomalies

Answer 3

1. Congenital Extrahepatic
   
   • eg. Portocaval, splenocaval, porto-azygous,
   • Portal blood drains into either the CVC or azygous vein with the shunt originating outside of the liver
2. Congenital Intrahepatic
   
   • Patent ductus venosus, left divisional, right divisional
   • Portal blood drains directly into the CVC within the liver
3. Portal Vein Hypoplasia
   
   • Can be seen with and without portal hypertension
4. Hepatic arteriovenous malformations
   
   • An hepatic artery has typically multiple communications with the portal vein resulting in a marked increase in portal pressures

Question 4

List the major clinicopathological abnormalities identified in dogs (and cats) with PSVAs.

Provide some pathophysiological explanation for the abnormalities

Answer 4

1. mild to moderate microcytic, normochromic, non-regenerative anaemia
   
   • Likely due to defective iron transport, decreased serum iron or decreased total iron binding capacity
2. leukocytosis / monocytosis
   
   • Likely to be seen with reduced hepatic clearance of bacterial endotoxin
3. Low BUN (70%)
   
   • Reduced hepatic conversion of ammonia to urea
   • Increased renal blood flow and increased GFR
4. Hypoalbuminaemia (50%)
   
   • Decreased functional hepatic mass
5. Hypocholesterolaemia
   
   • Decreased functional hepatic mass
6. Hypoglycaemia
   
   • Seen only with severe reducton in hepatic functional mass
7. Elevated liver enzymes - ALT and ALKP
8. Low USG
   
   • Increased GFR
   • Reduced medullary concentration gradient due to low urea
9. Ammonium biurate crystaluria / calculi
   
   • Seconary to increased ammonia excretion

Question 5

What diagnostic imaging options are available for the investigation of PSVA?

Note the limitations of each modality

Answer 5

1. Radiographs: can identify microhepatica and renomegaly, but not useful for assessing the vasculature
2. Ultrasound: Can identify both IHPSVA and EHPSVA along with HAVM.
   
   • Good sensitivity in experienced hands, while inexperienced operators may miss the diagnosis
   • Complete definition of shunt morphology may be difficult
3. Scintigraphy
   
   • Can identify shunting, but not specific for shunt morphology
   • Requires radio-isotopes and specialised equipment
4. Contrast-enhanced CT (CT angiography)
   
   • Gold standard
   • Minimal limitations apart from the requirement of anaesthesia in most cases
5. Magnetic resonance angiography
   
   • Less sensitive when compared to CTA and more expensive
6. Surgical portovenography or trans-splenic portovenography
   
   • rarely utilised due to availability of less invasive, more sensitive tests
   • Surgical requirement is the major limitation of the former
   • Caudally located EHPSVA may be missed with the latter

Question 6

List the various recommendations for medical management of dogs with congenital PSVA

Answer 6

1. Lactulose - orally for stable patients, retention enema for clinically significant HE
2. antibiotics
   
   • metronidazole, neomycin or amoxicillin/clavulanate
3. Gastroprotection
   
   • Proton pump inhibition most effective
   • +/- sucralfate if evidence of GIT ulceration
4. Seizure control - if necessary
   
   • Maybe avoid benzodiazepines
   • phenobarbitone / levetiracetam
5. Dietary management with highly digestible, plant based protein source. Avoid aromatic amino acids mainly found in red meat
6. Consider liver supportive medications including prednisolone if surgery is declined or not possible

Question 7

Describe the management options and considerations for dogs with hepatic encephalopathy secondary to PSVA

Answer 7

1.

Question 8

Describe the mechanism of action of the various management options for hepatic encephalopathy

Question 9

Describe the provide reasoning for the dietary recommendations for dogs and cats with hepatic encephalopathy caused by a PSVA