Hepatic vascular anomalies Flashcards
In a study by Freund 2020 in Vet Surg, did the application of a thin film to the external iliac vein of cats result in consistent occlusion by 8-weeks?
No - complete occlusion only in 1/6 cats despite the presence of granulomatous inflammation. Supports the theory that residual shunting may occur in cats after cellophane banding.
According to Matiasovic 2020 in Vet Surg, did thin film banding or ameroid constrictor for portosystemic shunt attenuation in dogs result in a higher rate of persistent shunting?
Thin film banding (29%) of dogs compared to 0% for ameroid constrictors.
Compare to the study by Otomo 2020 in Vet Surg which reported no difference in clinical outcomes between groups.
According to Mullins 2020 in Vet Surg, what was the 30 day survival in dogs suffering post-operative seizures following PSS attenuation? What were factors positively associated with short term survival?
32% of patients survived to 30 days.
Factors positively associated with survival included having preoperative seizures and development of focal PAS only.
In a study by Strickland 2020 in Vet Surg, what was the rate of PANS in cats treated for single congenital PSS? Was the use of perioperative levetiracetam associated with a decreased risk of PANS?
62% (5/31 did not survive to discharge)
Levetiracetam did not decrease the risk.
In a review of PANS by Mullins 2021 in Vet Surg what was the reported rate of PANS amongst all studies? What were 4 potential risk factors for development of PANS?
Reported rate of 2-27% (PAS rate of 0-18%).
Identified risk factors for development of PANS include preoperative hepatic encephalopathy, increasing age, certain breeds, and extrahepatic shunt morphology.
What are two blood tests suggested by Devriendt 2022 in Vet Surg that may be useful in determining complete EHPSS closure after treatment?
Serum hyaluronic acid and lidocaine/monoethylglycylxylidide test.
These can also be combined with fasted ammonia and serum bile acids for improved sensitivity and specificity.
In a study by Sunlight 2022 in Vet Surg, what post-operative biochemical changes were associated with excellent clinical outcomes following percutaneous transvenous coil embolization of IHPSS?
Increased protein-C,
Also, HCT, MCV, ALB, BUN
In a review by Mullins 2023 in Vet Surg, what are the reported rates of PANS and post-attenuation seizures in cats? What are two risk factors that have been identified for development of PANS?
Incidence of PANS is 14.3-62%, and postattenuation seizures is 0-32%.
Risk factors include post-operative osmolality, and lower grades of intraoperative postocclusion mesenteric portovenography.
In a study by Janas 2024 in Vet Surg, what 5 perioperative complications were reported following EHPSS attenuation with ameroid constrictors in 5 cats? What was the long term clinical outcome?
Perioperative complications reported including blindness, seizures, ascites, head pressing, and death.
The long term outcome was good to excellent in 16/18 cats.
In a study by Spies 2024 in Vet Surg, what were the two most common shunt EHPSS shunt configurations in dogs >15kg? What was the percentage of short term complications and shunt related deaths?
Portocaval and splenocaval were the most common morphologies (Golden retrievers most common breed).
Short term complications occurred in 36% of dogs and 7% had shunt related deaths. Portal vein hypoplasia was observed frequently on imaging.
In a study by Carrera 2022 in JAVMA, in dogs with PANS that survived for >30 days what percentage of neurologic signs present at the time of discharge ultimately resolved? What percentage of dogs survived >6 months? What percentage of dogs with initial seizures suffered recurrence?
67% of neurologic signs present at the time of discharge resolved.
90% of dogs survived >6 months.
50% of dogs with initial seizures had recurrence.
In a study by White 2020 in JSAP, at the level of the omental foramen what was the final vessel that communicated with the caudal vena cava in all cases of canine EHPSS? Label an image of the portal vasculature.
Regardless of the tributary vessels, the left gastric vein was the final vessel that communicated with the caudal vena cava in all cases.
In a study by Glenn 2022 in JSAP, what material was used for EHPSS occlusion in dogs as an alternative to cellophane? What was the mortality rate and rate of recurrence? What was the overall percentage of patients who had a good outcome?
Polyethylene band from the packaging of a urinary catheter was used.
Mortality rate was 7%, and recurrence rate was 17%.
Excellent or good outcomes were achieved in 82% of dogs.
In a study by Wilson 2021 in VRU, what imaging technique was used for anatomically characterizing canine hepatic vascular anomalies with similar results as CTA?
Ferumoxytol (a long acting MRI contrast agent) enhanced MR angiography.
In a study by Humphreys 2024 in VRU, what imaging finding was consistently identified in dogs with EHPSS?
A significant increase in the hepatic artery to aorta ratio. An increase in the hepatic artery is thought to be secondary to the arterial buffer response of the liver, which sees an increase in hepatic arterial flow in response to reduced portal flow.
In a study by Economu 2022 in JFMS, what was the most common shunt morphology in cats with IHPSS? What percentage of cats developed PANS after surgical attenuation? What percentage of cats had an excellent outcome post-operative?
Left divisional was most common. Acute attenuation was possible in 3 cats, whereas 8 underwent partial attenuation (of which 50% required a second surgery for complete suture ligation).
PANS developed in 50% of cats (17% died or were euthanized because of PANS).
Excellent outcomes were achieved in 63% of cats.
In a study by Serrano 2022 in JVIM, which of the following medical management options resulted in the greatest improvements in clinical signs for dogs with EHPSS?
1) Hepatic diet
2) Hepatic diet + lactulose
3) Hepatic diet + metronidazole
Hepatic diet and lactulose. Addition of metronidazole did not result in a further reduction in clinical signs.
Medical management was associated with reductions in fasting ammonia.
What is the largest portal vein tributary?
Cranial mesenteric vein
Are branches of the hepatic artery and bile ducts typically located on the ventral or dorsal surface of the portal vein?
Ventral
Describe the termination of the hepatic veins onto the vena cava?
The right lateral and caudate hepatic veins are completely surrounded by hepatic parenchyma.
Left-sided intrahepatic shunts most likely result from patency of which embryonic structure?
Ductus venosus (normally closes within 2-6 days after birth).
Portocaval and portoazygous shunts are inappropriate connections between which embryologic systems?
Cardinal and vitelline.
What is another term for portal vein hypoplasia (PVH) without portal hypertension?
Microvascular dysplasia.
In dogs and cats, what percentage of congenital single PSS are extrahepatic?
66-75%
Extrahepatic shunts are more common in small breed dogs, intrahepatic in large breed dogs.
What are the most common causes of acquired extrahepatic shunting?
Hepatic fibrosis (cirrhosis), PVH with portal hypertension (congenital noncirrhotic portal hypertension), and hepatic arteriovenous malformations.
What is the most common location for acquired extrahepatic shunts?
Usually multiple, tortuous vessels connecting a portal tributary directly to the renal vein or caudal vena cava near the kidney.
Name the following EHPSS.
What percentage of dogs with macroscopic congenital PSS have PVH-MVD?
58% of dogs, and 87% of cats.
What are the clinical signs for patients with PVH-MVD without PSS?
Often similar to PSS but may be less severe, present later in life and better long term prognosis with medical management alone.
Which dog breeds are predisposed to PVH-MVD?
Cairn Terrier, Maltese, Yorkshire Terrier.
What is hepatic arteriovenous malformation (AVM)?
Direct communication of the hepatic artery to the portal system through tens to hundreds of shunting vessels.
Results in arterialization of the portal vein, hepatofugal blood flow, and numerous acquired EHPSS formation.
How much liver function has to be lost for hepatic encephalopathy to occur?
> 70%
What is the effect of increased levels of ammonia with PSS?
Ammonia is excitotoxic and is associated with an increased release of glutamate, the major excitatory neurotransmittor of the brain.
With chronicity inhibitory factors such as GABA and endogenous benzodiazepines may surpass this excitatory stimulus and create signs more suggestive of coma or CNS depression.
Where is ammonia produced?
Produced by normal GI flora. Normally converted to urea and glutamine in the liver by the urea cycle.
What percentage of dogs with PSS had a hypercoaguable state?
43%
What dog breed is at highest risk for EHPSS?
Yorkshire terrier (36 x the risk of all other breeds combined).
In what dog breed are left-divisional intra-hepatic PSS considered heritable?
Irish wolfhounds and Australian cattle dogs.
Male dogs in Australia overepresented with right divisional PSS.
What are some potential causes of polyuria in dogs with PSS?
Poor medullary concentrating gradient due to low BUN, increased renal blood flow, increased ACTH secretion with associated hypercortisolism, psychogenic polydipsia from hepatic encephalopathy.
What percentage of dogs with hepatic AVM have abdominal effusion?
75%.
Also may occur with acquired shunting, or with severe hypoalbuminemia in cases of PSS.
What are some common clinical signs associated with PSS in dogs and cats?
CNS signs, GI signs (30% of dogs, less common in cats), GI hemorrhage in 30% of dogs with IHPSS, lower urinary tract signs, urinary tract calculi (36%), copper-coloured irises (particularly in cats), ptyalism very common in cats (75%).
What is the mechanism behind formation of ammonium urate urolithiasis?
Decreased production of urea, increased excretion of ammonia by the kidneys, decreased uric acid metabolism.
Which specific types of shunt morphology tend to have less severe clinical signs?
Portoazygous and portophrenic, due to possible compression by the stomach and diaphragm.
Shunts that insert caudal to the liver more likely to cause clinical signs than shunts inserting caudal to the diaphragm.
What clinical signs are common in patients with hepatic AVM?
Abdominal effusion (75%), GI signs often severe, hepatic encephalopathy reported less frequently than with PSS.
What are some common clinicopathologic findings in patients with PSS?
CBC: Microcytic normochromic nonregenerative anemia (60% dogs, 30% cats; generally not seen with PVH-MVD), target cells in dogs and poikilocytes in cats, leukocytosis.
Biochem: hypoalbuminemia (50%, uncommon in cats), reduced BUN (70%), hypocholesterolemia, hypoglycemia. Increased ALP and ALT (ALP > ALT in patients with PSS, and both values rarely >4x normal, ALT might be higher if acquired shunting is present).
Urinalysis: decreased USG, ammonium biurate crystalluria, proteinuria (secondary to immune mediated glomerulonephritis secondary to antigens reaching the kidneys that would normally be removed by the liver).
What percentage of dogs with PSS have increased renal blood flow and GFR?
81%
What liver function tests are recommended for assessment of suspected PSS?
- Bile acid testing (12-hour fasting and 2-hour postprandial).
- Fasted ammonia (only positive in 62-88% of animals with PSS) +/- ammonia tolerance test.
What might cause false/negative positive bile acid test results when assessing PSS?
Positive: Maltese dogs, inappropriate timing, other hepatobiliary disease, cholestasis, glucocorticoid or anticonvulsant therapy, tracheal collapse, seizures, GI disease.
Negative: lack of gallbladder contraction, delayed intestinal absorption due to prolonged transit time, inadequate food intake, delayed gastric emptying, malabsorption, maldigestion.
Which dog breed might have false positive results for fasting ammonia testing?
Irish wolfhound puppies (inborn error of ammonia metabolism).
What is the sensitivity of ammonia tolerance testing for PSS? When should this not be performed?
95-100%.
Should not be performed in patients with preexisting hepatic encephalopathy.
What two hepatic vascular anomalies can protein C be useful in differentiating between?
Normal dogs: >70% protein C activity
PSS: <70%
PVH-MVD: >70%
Deficiencies in protein can also be caused by increased consumption (DIC, thrombosis, surgery), renal disease and malignancy.
What radiographic findings are suggestive of PSS?
Microhepatica (60-100% dogs, 50% cats), bilateral renomegaly. Calculi may also be seen, but can be radiolucent.
What imaging techniques can be used for definitive PSS diagnosis?
- Ultrasound: more accurate at detecting IHPSS than EHPSS. Changes in flow direction (AVM) or velocity (IHPSS>EHPSS) may also be observed.
- Scintigraphy: transcolonic or transplenic injection of technetium pertechnetate. Shunt fraction 70-95% in dogs with PSS (normal in PVH-MVD).
- CT angiography.
- MRI
- Portovenography: operative mesenteric portovenography. Best performed in left lateral recumbency (100% sensitivity). May not detect PSS if transsplenic injection is used and shunt is upstream (although may opacify due to hepatofugal flow). Splenic injection can result in life threatening hemorrhage if AVM present.
What hepatic vascular anomalies are depicted by the scintigraphy images?
What diagnostic findings would indicate PVH-MVD in the absence of PSS?
Elevated bile acids, imaging negative for PSS, hepatic biopsy results consistent with PVH-MVD.
Describe the medical management of portosystemic shunts.
Why is it recommended to avoid use of diazepam in patients with hepatic encephalopathy?
Endogenous benzodiazepines and GABA may contribute to hepatic encephalopathy. Benzodiazepine antagonists (flumazenil) have been used to reverse hepatic encephalopathy induced comas.
What are the effects of lactulose in the medical management of PSS?
It is metabolized by colonic bacteria to organic acids. This results in acidification of the colonic contents, trapping of ammonia, and reduction in bacterial numbers. Its osmotic effect also produces catharsis, reducing fecal transit time and bacterial exposure to minimize ammonia production and absorption.
What is the median survival time for dogs with PSS treated with medical management alone?
9.9 months. In another study MST was 2.3 years for medically managed dogs, and wasn’t reached for surgically managed dogs.
Prognosis was better in dogs that were older at the time of diagnosis, had extrahepatic PSS, or higher BUN concentrations.
What are options for surgical shunt occlusion?
Ligation, ameroid constrictor, cellophane banding, hydraulic occluder.
What are methods of shunt localization during surgery?
Direct visualization, ultrasonography, operative mesenteric portography, evaluation of portal pressure changes.
Portal catheter placement through a purse string may also facilitate palpation of IHPSS location.
When would shunt attenuation be contraindicated?
Agenesis or atresia of the portal vein.
What is shown in the attached imagee?
Multiple acquired shunts. Normally identified near the kidney in the intestinal mesentery.
How can intraoperative portal pressures be measured?
Insertion of a catheter in a jejunal or splenic vein, or the portal vein.
What is normal baseline portal pressure?
8-13 cmH2O (6-10 mmHg)
What is the maximum dose of iodine that can be administered for mesenteric portography?
1200 mg of iodine per kg.
Overdose can cause hypotension, arrhythmias, cardiac arrest, and renal failure.
Can the use of intraoperative mesenteric portography help to predict outcome in dogs and cats undergoing PSS attenuation?
Cats: increased aborization following attenuation less likely to have neurologic complications and better clinical response to surgery.
Dogs: increased pre-ligation arborization associated with ability to completely occlude the shunt, but not related to clinical response. Deceased pre-ligation arborization associated with increased post-operative complications.
How much does swelling of the casein substance in an ameroid ring constrictor reduce the internal diameter?
32%. Remainder of closure of vessel due to fibrous tissue reaction.
How long does shunt attenuation take with ameroid constrictors and hydraulic occluders?
Ameroid constrictor: 2-5 weeks, most rapid during first 3-14 days.
Hydraulic occluder: 6-8 weeks (small amount of sterile saline injected every 2 weeks). Closure does not depend on fibrous tissue formation.
Why might use of cellophane banding not be ideal for use in cats with PSS?
Persistent flow has been reported in some cats, suspected secondary to reduced inflammatory response in this species.
What material should be used for suture ligation of PSS in cats?
Nonabsorbable synthetic monofilament suture due to the risk of recanalization in this species. Silk may be preferred in dogs.
What are visual intraoperative signs of portal hypertension?
Pallor or cyanosis of the intestines, increased peristalsis, cyanosis or edema of the pancreas, increased mesenteric vascular pulsations.
What are recommended post-ligation portal pressures for complete suture attenuation of PSS?
- Maximum portal pressure of 17-24 cmH20 (13-18 mmHg).
- Maximum change in portal pressure of 9-10 cmH20 (7mmHg).
- Maximum decreased in CVP of 1cmH20.
- Maximum decrease in arterial pressure of 5 mmHg or 15% or less.
- Heart rate should not increase dramatically.
How can doppler ultrasonography be used to help determine the degree of attenuation of a PSS intraoperative?
Degree of attenuation should be limited to a point where shunt flow becomes hepatopetal and cranial portal vein flow remains hepatopetal.
In what order are medications discontinued post-operatively for PSS?
Antibiotics, lactulose, then diet. Typically weaned over 2-3 months after surgery, based on bile acids, biochem and clinical signs.
Is normalization of bile acids following surgical correction of PSS associated with long-term outcome?
No, may remain elevated. Clinical outcome unchanged so long as clinical signs and biochemical parameters improve.
What are some complications associated with correction of PSS?
Hypoglycema (44% of dogs, 30% refractory to dextrose): treated with boluses of 25-50% dextrose, oral alimentation +/- glucocorticoids (EHPSS only).
Hemorrhage and anemia: surgical blood loss, sequestration/large fluid loads, coagulation deficits, GI loss.
Portal hypertension (2-14% of patients undergoing acute shunt ligation): treated with oxygen, warmth, IV fluids, hetastarch, GI protectants, analgesics, antimicrobials +/- FFP, whole blood. Ligature removal may be required. In mild cases treatment with spirinolactone may be adequate for management of ascites.
Seizures and encephalopathy (3-18% of dogs, 8-22% of cats): treated with boluses of midazolam or diazepam +/- levetiracetam, phenobarbital +/- propofol CRI. Mannitol to reduce intracranial swelling. Correct electrolyte abnormalities. In cases of severe hyponatremia causing seizures (<120 mEq/L), correct deficit slowly (<1 mEq/h).
Recurrence of clinical signs: continued flow, second shunt, acquired shunting, PVC +/- portal hypertension, unrelated disease.
What are clinical signs of portal hypertension following shunt attenuation?
Hypovolemic shock, abdominal pain, abdominal distension, diarrhea, vomiting, ascites.
Can be exacerbated by overhydration, bandaging, vocalization, defecation, large meals.
What are potential causes of post-operative PANS following PSS attenuation?
Decreases in endogenous inhibitor central nervous system benzodiazepines agonist levels, imbalances in excitatory and inhibitory neurotransmitters.
What is the perioperative mortality rate of dogs undergoing PSS correction?
Suture ligation: 2-32%
Ameroid: 7%
Cellophane: 6-9%
Mortality higher for IHPSS (~10-20%).
What is the long term outcome for patients undergoing PSS correction?
Generally good. Better for patients with complete shunt attenuation. Outcome more variable in patients undergoing surgery for IHPSS, although resolution of clinical signs are common despite persistent shunting.
What are some factors that influence the outcome of dogs undergoing PSS correction?
Large breed dogs more likely to have recurrence of clinical signs (although dogs >10kg had more favourable short term outcome for IHPSS attenuation).
Anemia associated with poorer long term outcome, increased BUN associated with decrease in short term survival with IHPSS.
Increased survival with greater preoperative albumin and total protein (IHPSS), risk of shunting increased with decreasing albumin (EHPSS; decrease of 1 g/dL = 4 x increase in odds of continued shunting).
Dogs with greater liver size more likely to tolerate acute shunt occlusion.
Animals tolerating acute shunt ligation normally have a better outcome.
What is the complication rate for cats undergoing PSS attenuation?
75%, most frequently PANS (seizures in 28%, blindness 44%). Blindness normally resolves within 2 months.
Mortality rates:
Ameroid = 0-4.5%
Cellophane: 0-22%
Suture ligation: 4-20%
In which liver lobes are AVM normally found?
Right or central divisional.
Multiple lobes affected in 20% of dogs.
What is the treatment for AVM?
Surgical resection of the affected lobe. Can be useful to temporarily occlude the nutrient artery prior to ligation to confirm that it is the source of the fistula (should see a rise in portal pressure).
What reflex might be observed following ligation of an AVM?
Branham reflex (treated with atropine or glycopyrrolate).
What percentage of dogs surgically treated for AVM require ongoing dietary or medical management post-operative?
75%
Which vessels is used for the approach for transvenous coil embolization of IHPSS in dogs?
Jugular.
What is the most common complication following transvenous coil embolization of IHPSS?
Coil migration (reduced with the use of caval stenting). Portal hypertension is rare.
When measuring the venal cava for stent placement during transvenous PSS coil embolization, should measurements be obtained under positive pressure ventilation?
Intraabdominal measurements should be obtained under 20 cmH20 of positive pressure ventilation, thoracic measurements should be obtained without.
What portal pressure measurements are the end-goal of tranvenous coil embolization for PSS?
- Increase in portal pressure of 10 cmH20 (7 mmHg).
- Final portal pressure of 20 cmH20 (15 mmHg).
Note: coiling should only be performed if initial caval to portal pressure gradient is less than <6-7 mmHg.
Addition of coils is required in what percentage of cases following transvenous coil embolization for PSS?
18%
3% of shunts can undergo complete occlusion (portal perfusion is well developed on angiography).
What is the complication rate following transvenous coil embolization for PSS?
15% complication rate: coil migration, bleeding from the jugular catheter, post-operative neurologic activity (6%), GI bleeding/signs (increased risk with decreasing albumin concentrations).
Portal hypertension not typically seen.
What is the perioperative mortality rate following transvenous coil embolization for PSS?
5%. Normally due to GI bleeding, cardiac arrest, or continued neurologic signs.
What interventional radiology technique has been described for the treatment of hepatic AVM?
Cyanoacrylate glue embolization. Typically performed via the femoral artery.
What is the outcome following cyanoacrylate embolization of hepatic AVM?
Generally good although most dogs require lifelong medical management due to acquired shunting.
Nontarget embolization is the main complication, but is rarely clinically significant.
