Liver Vascular Malformations Flashcards
The liver receives 20% of its blood supply from A) the - a branch of the B).
A) Hepatic a.
B) Coeliac a.
The hepatic artery branches at the porta of the liver to supply each lobe. This is under A) pressure. The other 80% of blood comes from the B) which entirely drains the gastrointestinal (GI) tract (from stomach to cranial rectum), pancreas and spleen.
A) High
B) Low pressure portal vein
What is the normal direction of the blood supply in the portal vein?
Towards the liver (hepatopetal)
In the absence of valves in larger vessels; which direction does blood travel? (pressure)
High –> Low
Where does the left phrenic vein drain blood from and into?
diaphragm into the caudal vena cava
Define portosystemic shunt
An anomalous vessel which allows blood to bypass some, or all, of the liver
What is the difference between intra and extra PSS?
Portosystemic shunts can occur inside the liver parenchyma (intra-hepatic) or outside of the liver parenchyma (extra-hepatic)
Generally PSS are what type in small breeds?
Extra hepatic
Generally PSS are what type in large breeds?
Intra hepatic
Most common breed type for PSS?
Toy/miniature
What age do patients tend to present with PSS?
1-2 yr
What do acquired PSS tend to happen as a result of?
Severe chronic hepatic dx
How does an acquired PSS develop?
Non-functional connections exist in the foetus and will remain quiet in the adult unless chronic portal hypertension develops
How many shunts are common with acquired?
Multiple
T or F:
Surgery is indicated for acquired PSS?
False
How many shunts are common with congenital PSS?
Commonly 1
How are congenital intra hepatic shunts be classified?
Right
Central
Left
What do all 3 types of intra hepatic PSS connect the intra-hepatic portal system to?
Vena cava
What are the 4 classifications of extra heptatic PSS that 94% can be classified as?
Spleno-caval
Left gastro-phrenic
Left gastro-azygous
Right gastric vein based shunts.
In the spleno-caval shunt, where is the shunt?
From part of the left gastric vein, near the splenic vein - the blood is diverted straight into the caudal vena cava, from a more central part of the left gastric vein
(the shunting vessel is not actually direct from the splenic vein to the caudal vena cava.)
What is the anatomy of a gastro-phrenic EHPSS?
Connection of the L gastric –> L phrenis –> Caudal VC
At which anatomical landmark do you think a right gastric vein-based shunt enters the caudal vena cava?
Epiploic foramen
What happens with a R gastric bein EHPSS
A right gastric vein-based shunt has a connection to the caudal vena cava in the same location as the spleno-caval shunt, but the direction of blood flow and development of shunting leads to a distended right gastric vein
The azygous vein runs as a parallel system to the caudal vena cava, draining blood from the ?
vertebrae
The azygous vein passes through the A) and ends at B) with the vena cava
A) aortic hiatus
B) right atrium
What happens with a left gastro-azygous EHPSS?
The shunting vessel joins the azygous vein in the thoracic cavity. It goes through the aortic hiatus to get there.
The small phrenicoabdominal veins enter the caudal vena cava approximately 1cm cranially to the renal veins. Moving cranially, there should be no further vessels entering the vena cava until you reach the ? Any vessels in-between can be considered anomalous.
hepatic veins.
Common signs of a PSS? (6)
Hepatic encephalopathy (HE) – present in the majority of affected dogs
Chronic gastrointestinal signs – anorexia, vomiting
Lower urinary tract signs associated with urate urolithiasis in 40% of cases
Retarded growth, weight loss
Ptyalism and central blindness in cats
Polyuria/polydipsia
Common findings on CE with PSS? (3)
Microhepatica (more common in dogs than cats)
Prominent kidneys
Copper coloured iris in cats.
Finding on haematology with PSS? (2)
Mild to moderate, microcytic, normochromic nonregenerative anaemia
Leucocytosis
Findings on coag profile with PSS?
Are usually normal but dogs with PSS may have prolonged APTT
Biochem findings with PSS? (8)
Bile acids (fasting and post prandial) – elevated
Ammonia (where available) – elevated
Hypoalbuminaemia (50% of dogs, less common in cats)
Decreased BUN (70%)
Hypocholesterolaemia
Hypoglycaemia
Mild to moderate increase in liver enzymes (e.g. ALT)
Protein C activity is a sensitive test for liver insufficiency and is usually lower in dogs with a PSS.
Post-prandial bile acids are typically what with PSS?
> 100 µmol/L
why is a decreased BUN seen with PSS?
Reduced conversion to ammonia to urea and PUPD seen in many patients
What are bilirubin levels in PSS?
Often normal
How can protein C levels be used for PSS?
what is the limitation of this test? (2)
Sensitive test for liver insufficiency; lower in dogs
Currently shipped to USA
Expensive
Common USG findings with PSS? (4)
Decreased USG
Proteinuria
Urate crystals
Sulphated bile acids (cat)
What fasting indicators give a good idea of shunt?
Inreased ammonia
increased bile acid
When using u/s for PSS; what else should be checked?
Renal pelvis + Bladder for urate stones
What is now considered by many the imaging modality of choice for portosystemic shunts?
CT angiography
What imaging type is still useful if the shunt cannot easily be located during surgery or to ensure correct the vessel has been ligated?
Traditionally intra-operative portography was used to locate the shunt. Iodine is injected into a catheter in a mesenteric vein followed by radiography or fluoroscopy.
Nuclear scintigraphy has been used to detect PSS. Radioactive iodine is introduced how? (2)
Transcolonic – via the rectum
Splenic – direct injection into spleen.
T or F
Dogs with shunts can have no abnormalities on haematology but there are always changes in biochemistry.
False
PSS T OR F
Animals with shunt can present hypoalbuminemia.
True
What are considered medical treatments for a diagnosed portosystemic shunt? (3)
Lactulose
ABx
Low/modified protein diet
How id lactulose beneficial for PSS?
Traps ammonium ions in the colon and reduces the production and absorption of ammonia by speeding up the gut transit time.
Why are ABx used for PSS?
Reduce enteric flora and toxins which cause HE.
Which ABx can be used for PSS? (3)
ampicillin, metronidazole, neomycin
Discuss a suitable protein diet for PSS?
A modified protein sources which are less ammoniogenic such as Purina HA (a hydrolysed soya-based diet).
What is an anticonvulsant drug used to pre-load patients with the aim of decreasing peri/post-operative seizures?
Levetiracetam
Aim of PSS surgery?
To slowly close the anomalous vessel to gradually accustom the liver to the increased blood supply
What type of closure is performed in most cases?
Partial attenuation
What procedure can be done for porto-azygos shunts during the first surgery but for most other shunts it is done during a second operation if a gradual occluding device is not used.?
Complete attenuation
4 aims of PSS surgery?
1 Identify the anomalous vessel;
2 Reduce the blood flow in the anomalous vessel;
3 Verify that the portal system communicates with the liver at some point other than the shunt;
4 Obtain a liver sample for histopathology
histopathology can be useful to assess for concurrent hepatopathy, which may affect prognosis. Which breed is this particularly the case in?
Maltese
Careful retraction of the ? reveals the shunt entering the caudal vena cava from the left side
mesoduodenum
Which 2 shunts both terminate in the same anomalous connection from the left gastric vein to caudal vena cava?
Spleno caval
Right gastric vein
Where to look on the LHS for PSS? Use anatomy.
This is always caudal to the hepatic veins and cranial to the small phrenicoabdominal veins which enter the caudal vena cava approximately 1 cm cranially to the renal veins. There should be NO other vessels entering the vena cava between the small phrenicoabdominal veins and the hepatic veins, thus any vessels found between these landmarks can be considered anomalous.
What artery may need careful dissection from the shunting vessel to allow access at the epiploic foramen?
Coaliac
What shunt is present at the oesophageal hiatus?
L gastric phrenic
What shunt is present at the aortic hiatus?
L gastro azygous shunt
Surgical approach to the aortic and oesophageal hiatus?
Ventral celiotomy
Surgical approach to the aortic and oesophageal hiatus:
A) What organ is temporarily removed from the abdomen?
B) How to pull the stomach caudually?
C) What ligament is cut?
A) Spleen
B) Stay sutures in the fundus
C) Left triangular ligament of liver
Left-gastro-phrenic shunts typically can be attenuated where?
Where does this shunt typically run?
the anomalous left gastric vein meets the left phrenic vein.
The shunt typically runs ventral and adjacent to the gastro-oesophageal junction.
Where do Gastro-azygous shunts typically run?
Adjacent to the gastro-oesophageal junction before entering the aortic hiatus ventral (i.e., nearer surgeon) to the aorta.
These shunts generally pass ventral to the gastric cardia but may also pass dorsally or rarely to the right (when opening of lesser omentum may be needed).
Where can gastro-azygous shunts be attenuated?
as near the diaphragm as possible, ensuring no vessels bypass the site of attenuation.
2 ways to surgically approach a gastro-azygous shunt?
- Ventral celiotomy
- In the thorax at the level of the insertion in the azygos vein.
What are the two options for gradual attenuation of extra-hepatic vessels?
Ameroid ring constrictor placement
Thin plastic film (“cellophane band”) placement
What size ameroid constrictor in small dogs?
3.5-5mm
What is an ameroid constrictor made of?
An inner casein ring and stainless steel external sheath.
How does an ameroid constrcitor ring work?
The ring’s internal diameter reduces due to modification of its inner structure after interaction with normal physiological fluids thereby constricting the vessel. Further constriction occurs due to fibrosis of the vessel itself. There should be minimal dissection around the shunt to prevent the ring moving around causing kinking and sudden occlusion
What is the risk of rapid occlusion of a PSS?
Increased risk of an acquired shunt
How does the cellophane band work?
A 10 x 1.2 cm piece of sterilised plastic film is obtained and folded into a three-layer strip approximately 4mm wide. It is placed around the shunt and constriction is a result of foreign body reaction and fibrosis.
How to use sutures for PSS? What needs to be monitored?
Complete suture occlusion may be achieved in up to 50% of cases with careful monitoring; partial suture occlusion, with a pre-placed loose suture to be tightened at a second surgery in 3 months can also be done.
MONITOR - portal hypertension
Peri-operative complications of PSS? (5)
Hypothermia
Hypoglycaemia
Haemorrhage
Portal hypertension
Seizures
Signs of portal hypertension in surgery? (4)
- Pallor
- Peristalsis increased
- cyanosis/oedema of pancreas
- increased vascular pulsations of mesenteric vasc.
Ensure the entire abdominal venous system is checked at surgery. Why?
You cannot ligate a PSS if the portal system is not connected to the liver at another location!
True or False
Diazepam is most often ineffective for controlling the related and peri-operative seizures.
True
Post op complications of PSS? (4)
Ascites
Residual shunting not addressed (may or may not be clinically significant)
Development of multiple acquired shunts
Continued flow through original shunt
Aim of intrahepatic shunt surgery
The principle of surgery on intrahepatic shunt is to attenuate either the feeder vessel (branch of the portal vein) or the draining vessel (hepatic vein) as it is most often impossible to isolate the shunt (due to its intrahepatic nature).
Treatment recommendation for intra-hepatic PSS?
Percutaneous trans jugular coil embolisation
How do Percutaneous trans-jugular coil embolisation work?
The coil physically reduces the diameter of the shunt and subsequent thrombus formation occludes it further. The coils are “caged” in the shunt and prevented from moving back into the cava by the use of a caval stent which interstices prevent mifgation of the shunts.
Where are LESS common extra heptaic PSS? (2)
Portal system to:
Iliac vein or Cd Vena cava
What is Portal vein hypoplasia/hepatic microvascular dysplasia?
The blood is shunted within the liver, but at a widespread microscopic level (compare to the macroscopic shunting of intra-hepatic portosystemic shunts just described).
Portal vein hypoplasia/hepatic microvascular dysplasia: Breed pre disposition (2)
Yorkshire terrier
Cairn terrier
Hepatic arterio-portal malformation (HAPM)
A) How common?
B) What are the 2 pathogenesis?
A) VERY uncommon
B) Congenital (more common) or acquired (single fistula - rare)
Treatment of :
Hepatic arterio-portal malformation (HAPM)
a combination of transarterial embolisation and surgical closure of the dominant outflow vein (part of the portal vasculature which is directly connected to the arterial system).
When is liver lobectomy fro Hepatic arterio-portal malformation (HAPM)ppropriate?
Liver lobectomy, which was previously one of the treatments of choice, is not recommended anymore, unless the HAPM is very circumscribed.
