25. Vascular liver diseases, portosystemic shunt in dogs and cats. Hepatic encephalopathy Flashcards
Portal hypertension causes?
Portal Hypertension
Elevated blood pressure in the portal system
Normal range: 5-10 mmHg
Portal hypertension is defined as when the portal blood pressure is 5
mmHg higher than the BP in the inferior vena cava
Composition of the portal system?
COMPOSITION OF THE PORTAL SYSTEM
§ Portal vein § Splenic vein
§ Superior mesenteric vein § Left gastric vein
§ Inferior mesenteric vein § Umbilical vein
Aetiology of portal hypertension?
AETIOLOGY
When blood flowing from the portal system → inf. vena cava meets resistance
The causes of portal hypertension can be categorised by their aetiology
Pre-hepatic causes
Occurs before blood arrives to the liver
§ Portal vein thrombosis
§ Splenic vein thrombosis
§ Arteriovenous malformation
§ Splenomegaly
Intra-hepatic causes
Occurs due to causes affecting the liver specifically
§ Cirrhosis by viral hepatitis; metabolic disease; (alcohol)
§ Primary sclerosing hepatitis
§ Schistosomiasis
§ Nodular regenerative hyperplasia
Post-hepatic causes
Due to problems involving the vena cava
§ Inferior vena cava obstruction
§ RS-HF
§ Hepatic vein thrombosis
Clinical signs of portal hypertension?
CLINICAL SIGNS
May be asymptomatic; CSx are usually related to the underlying disease (usually cirrhosis)
§ Hepatosplenomegaly § Fatigue
§ Nitric oxide release § Pruritis
§ Swollen capillaries § Oedema
§ Caput medusae § Ascites
§ Palmar erythema § Jaundice
Portosystemic shunt(PSS)?
Portosystemic shunt (PSS)
Abnormal vascular communication between the portal & systemic venous systems
May be acquired or congenital; Intrahepatic or extrahepatic
Consequences
↑ In toxins in the systemic circulation
§ Mercaptan § NH3
§ Benzodiazepine § GABA
§ SCFA (short chain fatty acids)
↓ Hepatic blood flow → Hepatic atrophy
Congenital PSS?
CONGENITAL PSS
75% of PSS cases (more common)
Caused by abnormal embryonal blood vessels; Associated with portal hypertension; May be intra-hepatic or extra-hepatic
Young > Old
Intrahepatic PSS
Always solitary
§ Persistent embryonal ductus venosus
§ Left, central & right division: Left division morphology is
consistent with failure of ductus venosus closure
Predisposed: Large dogs > Small dogs
Irish wolfhound; Golden retriever; Irish setter; Labrador; Old English
sheepdog; German Shepherd
Extrahepatic PSS
Always solitary
Anatomically abnormal communication between the portal system
and v. cava caudalis or v. azygous
Predisposed: Small & toy dogs > Large dogs; Cats
Yorkie; Cairn terrier; Shih Tzu; Maltese terrier; Pug; Mini
Schnauzer; Poodle
Acquired Pss?
ACQUIRED PSS
Multiplex, collateral vessels; Narrow & twisting
Protective compensatory response to portal hypertension; See also
arterioportal fistula (APF) later
Predisposed: Old animals > Young animals
Hepatic microvascular dysplasia?
Other Vascular Diseases
HEPATIC MICROVASCULAR DYSPLASIA (HMD)
Special form of congenital hypoplasia to the portal vein
Ø Portal hypertension
Formation of intralobular microvascular shunts form
Predisposed: Small breeds > Large breeds
Cairn terrier; Yorkshire terrier
CSx: Ø CSx or may be mild
Dx
§ Lab. D: ↑ BA
§ US: Trans-colonic portal scintigraphy normal; Ø
Macroscopic shunt
§ Biopsy
Tx: Diet; Lactulose
Arterioportal fistula?
ARTERIOPORTAL FISTULA (APF)
Connection forms between A. hepatica & V. portae
Congenital
Leads to:
§ Portal hypertension
§ Ascites
§ Acquires PSS
§ GI oedema
CSx: Continuous murmur (fremitus) (turbulent flow over the affected
liver lobe); GI oedema; Ascites
Dx: US: Hepatic AV fistula: Distended, twisting, echo-loose portal
branch within a liver lobe; Hepatofugal blood flow* above the liver
lobe
*Hepatofugal blood flow is abnormal flow of blood is from:
Periphery of the liver → Porta → Backwards along v. portae
Tx: Lobectomy; Treatment of portal hypertension
Hepatic venous outflow obstruction?
HEPATIC VENOUS OUTFLOW OBSTRUCTION
Budd-Chiari-like syndrome
Young dogs > Older dogs
Abnormal development of vessels before differentiation into veins &
arteries
↑ Arterial pressure → Dilation of portal branch + hepatofugal flow
Frequently with arterioportal fistula & primary hypoplasia of the
portal vein (PHPV)
Diagnosis
§ Colour doppler US; Celiac arteriography; Laparotomy
§ Biopsy: Thick-walled arterial vessel; Dilated venous
vessels; Fistula
§ Lab. D: Mild anaemia; Leucocytosis; Hypoproteinaemia;
Normal liver enzymes; ↑ BA
Hepatic encephalopathy?
Hepatic encephalopathy
Metabolic dysfunction of the brain due to liver dysfunction
Can occur when 70% of hepatic function is lost
May be caused by any hepatic disease, but more commonly PSS or
hepatic toxicosis
Younger animals: Caused mostly by shunts
Older animals: Caused mostly by neoplasia or cirrhosis
Acute hepatic Encephalopathy?
ACUTE HEPATIC ENCEPHAOPATHY
Rare (<10% of cases); Acute liver failure
Pathophysiology
Cause: Liver necrosis (diffuse; severe; 70-80% of the liver) (this
could be caused by toxins, infection, drugs or ischaemia)
Severe brain oedema then leads to ↑ intracranial pressure
Clinical signs
See CSx associated with Grade 3 & 4 HE later
§ Seizures
§ Semi-coma; Coma
Diagnosis
§ Lab. D: ↑ NH3!
Chronic Hepatic encephalopathy?
CHRONIC HEPATIC ENCEPHALOPATHY
More common (90% of cases)
Portosystemic shunt + ↓ Liver function
Pathophysiology
Portosystemic hepatic encephalopathy (PSE) → Chronic Hepatic encephalopathy → Portosystemic vascular anastomosis (allowing the
diversion of portal blood into the systemic circulation) → HE
Dog: High reserve capacity (preventing HE from developing in most
cases); In rare cases, there may be a congenital urea cycle enzyme
deficiency
Cat: Lower reserve capacity; Congenital enzyme deficiency means
that arginine isn’t synthesised in the liver ∴ inadequate NH3
detoxification
Anorexia → ↓ Arginine → Hepatic lipidosis → ↑NH3
Finally: Leads to deranged neurotransmitter systems
Clinical signs of hepatic encephalopathy?
CLINICAL SIGNS OF HEPATIC ENCEPHALOPATHY
Episodic intensity & severity
CNS signs are attributed to the deranged neurotransmitter systems,
brain oedema and hypoglycaemia. These clinical signs are expressed
as differing grades of hepatic encephalopathy. These are shown in the
table below.
Grade of HE Clinical signs
1 Lethargy; Apathy; Depression; Personality
changes; PU; Anorexia
2
Ataxia; Disorientation; Compulsive pacing;
Circling; Head pressing; Apparent blindness;
Personality changes; Salivation; PU
3 Stupor; Severe salivation (cats); Seizures
4 Coma; Non-responsive
Other clinical signs
§ Anorexia § Vomiting
§ Weight loss § Ptyalism
§ Diarrhoea § PU/PD
§ Urolithiasis § Cystitis
§ Stranguria § Dysuria
§ Haematuria § Pollakiuria
§ Crystalluria
Lab D of hepatic encephalopathy?
LAB. D OF HEPATIC ENCEPHALOPATHY
Haematology: Non-regenerative microcytic anaemia; Acanthocytes;
Poikilocytosis
Biochemistry
Hepatocellular dysfunction
§ Normal or ↑↑ ALP; ↑↑ALT; ↑↑AST; ↑↑GGT; ↑↑Br
§ ↑ BA; ↑ NH3
§ Signs of liver dysfunction: ↓ BUN; ↓ Urea; ↓ Chol;
↓ Albumin; ↓ Blood glucose; Coagulopathy
Urinalysis
§ ↓USG: Isosthenuria; Hyposthenuria (PU/PD)
§ Ammonium-biurate crystals
§ Urolithiasis: Haematuria; Proteinuria; Pyuria
Liver function tests
↑ NH3; ↑ BA
§ Ammonia tolerance test (ATT)
§ Post prandial ammonia tolerance test (APTT)
↑ BA
§ Fasting BA
§ Post prandial BA
↓↓ Protein C
