Liver

Provide definitions for the following terms

Term	Definition
Liver disease
Liver failure (aka. hepatic insufficiency)
Acute liver failure/disease Appearance
Chronic liver failure/disease Appearance
Cirrhosis (end-stage) liver Appearance
Cholestasis
Hepatitis
Cholangitis
Cholangiohepatitis
Cholecystitis

Term	Definition
Liver disease	Very BROAD term describing ANY disease process affecting the liver Does NOT indicate chronicity or degree of liver function ± Clinical signs or blood changes May be macroscopic or only microscopic changes
Liver failure (aka. hepatic insufficiency)	Severe liver disease where >70 - 80% of functional liver is lost USUALLY associated with clinical signs and changes in bloods
Acute liver failure/disease Appearance	Hepatic dysfunction develops RAPIDLY (usually without pre-existing liver disease) Gross appearance: Liver looks NORMAL (no time for remodelling and changes)
Chronic liver failure/disease Appearance	Hepatic dysfunction develops SLOWLY over months/years due to progression of liver disease or damage Gross appearance: Small, fibrotic and firm
Cirrhosis (end-stage) liver Appearance	Chronic and irreversible result of progressive liver disease → Diffuse hepatic fibrosis Gross appearance: Bands of small, pale, firm liver (fibrosis) with interspersed nodules of regenerating liver parenchyma
Cholestasis	Reduced bile secretion and flow → Accumulation of bilirubin and bile acids in blood Usually caused by biliary obstruction
Hepatitis	Inflammation of the liver parenchyma (acute OR chronic)
Cholangitis	Inflammation of the biliary tract
Cholangiohepatitis	Inflammation centred on the biliary tract with extends to involve the adjacent hepatic parenchyma
Cholecystitis	Inflammation of the gallbladder

Which sheep has acute liver disease? Which has chronic liver disease?

Flossie = Acute liver disease

• Bronzer and swollen

• ± More friable

Jezebel = Chronic liver disease

• Small, pale and friable

4 Macroscopic features of a NORMAL liver

1. Smooth outer capsule

2. Dark red-brown parenchyma divided into lobes (varies between species)

   • Ruminant = Left (ventral) and right (dorsal)

     • Gallbladder protrudes from RIGHT lobe

   • Camelid = Lobe fimbriation (frilly edges)

3. Sharp (tapering) lobe edges

   • Round margins = Swelling

4. Firm-ish texture (can place finger through)

4 Species that lack a gallbladder

“HARD”

1. Horse

2. Alpaca → Continuous secretion of bile

3. Deer

4. Rats (not mice)

2 Gallbladder features to assess in PM

1. Ensure patency

2. Oedema around gallbladder = Shock

Microscopic Structure of the Hepatic Lobule

• Hepatocytes

• Sinusoids

• Kupffer cells

• Bile flow

Hepatocytes: Long-lived epithelial cells making up most of the parenchyma

• Arranged in plates (1 cell thick) separated by sinusoids

• Metabolically active (eg. bile production)

• Good regeneration

Sinusoids: Fenestrated liver capillaries through which blood flows and separate hepatocyte plates

• = Blood from portal vein and hepatic artery (infarction difficult due to duel blood supply)

Kupffer Cells: Liver-resident macrophages within sinusoids which phagocytose aged/damaged RBCs and pathogens

Bile: Produced by hepatocytes → Bile canaliculi → Larger bile ducts → Gallbladder OR directly into the duodenum via the bile duct

• Gallbladder = Concentrates and stored bile

Hepatic Lobule

• Structure

• Portal area

• Central vein

• 3 Zones of hepatocytes (+ hypoxia)

  • Toxin exposure

Structure: Each composed of thousands of hepatocytes arranged into a rough hexagon and separated by other lobules with connective tissue

• Grossly observable in pigs

Portal Area: Each corner of the hexagonal hepatic lobule makes up a portal area which contains branches of:

1. Hepatic artery*

2. Portal vein*

3. Bile ducts*

4. Lymphatic vessels

Central Vein: Branch of the hepatic vein located at the centre of each hexagonal liver lobule which drains blood

Zones:

1. Periportal hepatocytes

2. Midzonal hepatocytes

3. Centrilobular hepatocytes (around central vein)

   • Contain enzymes involved in drug metabolism

   • Most susceptible to hypoxia as they receive blood (O2) last (periportal zones receive oxygenated blood first)

Toxins: DIFFERENT regions susceptible depending on the specific toxin

• Although periportal area receives toxin first (eg. from GIT), different parts of the lobule have different enzymes for toxin metabolism

Blood flow vs. bile flow in the hepatic lobule

Blood flow = Within hepatic sinusoids from the outer portal areas INWARDS towards the central vein

Bile flow = Moves from the centrilobular regions OUTWARDS towards the portal areas

Describe FIVE functions of the liver

1. Bile and bilirubin formation, secretion and metabolism

   • Bile = Water + cholesterol + bile acids + degraded waste products (eg. bilirubin)

     • Functions:

       1. Lipid digestion in intestine (bile acids) → Resorption and recycling

       2. Waste and toxin excretion (bilirubin)

2. Carbohydrate, lipid and vitamin metabolism

   • Synthesis of glucose, cholesterol, vitA, B12, D and K

3. Protein synthesis and secretion

   1. Albumin

   2. Coagulation factors for haemostasis (FII, VII, IX and X)

   3. Ammonia released from protein breakdown → Urea

4. Detoxification and "safe" body storage = Liver's position and bloody supply allow it to detoxify/modify substances absorbed from the GIT before they enter systemic circulation

   1. Excretion of waste products, drugs and toxins in bile OR urine (liver makes insoluble toxins soluble → allows elimination from circulation by kidneys in urine)

   2. Storage of substances (eg. iron and copper)

5. Immunity

   1. Production of acute phase proteins

   2. Hepatic location of cells of adaptive/innate immune systems (eg. Kupffer cells and lymphocytes)

Supply and drainage of liver blood supply

Liver receives blood from TWO main sources:

1. Portal vein = Drains GIT and provides 75% of the blood that the liver receives (nutrient-rich and O2-poor)

2. Hepatic artery = Provides remainder of blood to liver (O2-rich) Hepatic vein = Vessel which drains the liver of blood → Caudal vena cava → Heart

List 3 long-term (chronic) responses of the liver to injury

1. Regeneration

2. Fibrosis

3. Biliary hyperplasia

What is this?

• Growth response

• Indication

• Gross appearance

• Outcome

Regeneration

Growth Response: Hyperplasia (increased number of cells)

Cause: Mild/short-lived hepatic injury will resolve quickly through regeneration assuming sufficient ECM is intact

Gross Appearance: Nodules of new liver as surviving hepatocyte form islands to produce more (mistaken for neoplastic masses)

Outcome: Up to 70% of liver can be surgically removed without serious consequences → Return to normal size and function within a few weeks

What is this?

• Cause

• Gross appearance

• Outcome

Liver Fibrosis

Cause: Chronic/severe injury → Hepatic necrosis

Gross appearance: Affected parts of liver are firmer, paler and smaller than normal (distribution affects nature of causative injury)

Outcome: Fibrosis (collagen) replaces functional hepatobiliary function

Biliary Hyperplasia

• Definition

• 3 Causes

• Gross appearance

Definition: Injury to bile ducts → Proliferation of bile ductules in portal triads ± fibrosis

Causes:

1. Obstruction

2. Severe hepatocyte injury

3. Portal inflammation

Gross appearance: NONE! (only microscopic)

3 Potential outcomes of liver injury + causes

1. Resolution = With regeneration of damage liver and return to normal function

2. Irreversible progression (end-stage liver/cirrhosis) = Loss of normal lobular architecture due to replacement by extensive fibrosis ± nodular regenerations

3. In-between = Part of liver is severely damaged → Fibrosis not regeneration BUT other parts unaffected → Regeneration

When are clinical signs of hepatobiliary damage evident?

Liver has large functional reserve → Clinical signs only apparent when damage is severe and advanced (heading towards liver failure) OR there is cholestasis

5 Clinical signs of mild liver disease

Clinically silent OR mild, intermittent or non-specific signs

1. Anorexia

2. Weight loss

3. Lethargy

4. Vomiting

5. Diarrhoea Similar clinical signs as other body systems (eg. renal and GIT)

4 Additional tests to confirm suspicion of hepatobiliary disease due to mild/non-specific clinical signs)

1. Bloods (CBC and biochemistry ± urinalysis)

2. Imaging of liver and associated structures (eg. U/S for liver margins, cannot see parenchyma well)

3. Sampling liver (FNA for cytology or biopsy for histology)

4. ± Exploratory laparotomy

Describe FOUR clinical signs of advanced liver failure (>70 -80% loss of liver function)

• Pathogenesis

• Clinical signs

1. Oedema

   • MoA: Failing liver cannot produce enough albumin to maintain COP → Hypoalbuminaemia → Fluid leakage from vessels Ascites #1

   • Clinical Signs: Ascites #1

2. Neurological Signs = Hepatic Encephalopathy

   1. MoA: Ammonia produced from protein breakdown → Failing liver cannot convert ammonia and other toxins from the blood into non-toxic metabolites (eg. urea) → Toxins remain in blood and cross BBB → Neurotoxic

   2. Clinical Signs: Altered behaviour, depression, head-pressing, pacing, aimless wandering, ataxia ± seizure

3. Increased Bleeding

   • MoA: Failing liver cannot produce enough coagulation factors required to achieve haemostasis → Haemorrhage

   • Clinical Signs: Pale MM, haemothorax, haemothorax, joint haematoma, prolonged bleeding from wounds

4. Photosensitisation in Production Animals

Ascites caused by FIP vs. liver disease

Although liver disease is associated with FIP, there is not liver failure

• Ascites is due to increased vascular permeability (inflammation) NOT liver failure

Leakage vs. Induction Liver Enzymes

• 3 Examples

• Function

• Duration of formation

Leakage Enzymes = Leak into blood when hepatocytes are damaged/die

1. ALT = Alanine aminotransferase

2. AST = Aspartate aminotransferase

3. GLDH = Glutamate dehydrogenase

Function: Indicate hepatocellular damage

Duration: RAPID increase after event (hours)

Induction Enzymes = Synthesis increases (induced) in response to damage/stimuli due to bile retention (or various drugs)

1. ALP = Alkaline phosphatase

2. GGT = Gamma glutamyltransferase

Function: Indicate cholestasis

Duration: Longer to increase after cholestatic event (>1d) as enzymes must be induced/synthesised

• HALT HaMSTers with SCALPelS

  • HALT = Hepatocellular ALT

  • HaMSTers = Hepatocellular and Muscle (A)ST (also used in equine and ruminants)

  • SCALPelS = Steroids, Cholestasis, ALP elevates (+ Skeletal)

• GLDH = L and H for liver/hepatocellular

• GGT = CCC

4 Disadvantages of serum liver enzyme tests

1. NOT specific for liver damage/cholestasis (may increase when there is nothing to do with the liver i.e 2˚)

2. Species variation in liver specificity of enzyme increase and serum half-lives

3. Do NOT indicate prognosis (i.e. if liver damage is reversible or not)

4. Do NOT indicate how much functional liver tissue is present still (i.e. do NOT test for liver function)

Leakage Enzymes = ALT, AST, GLDH

• Function

• Lifespan

• Disadvantage

• DDx for elevation

ALT

Function: Liver-specific leakage enzyme reflecting acute hepatocellular injury/death in cats and dogs

• NOT useful in large animals

Lifespan: Increases within 12hr of SINGLE liver injury → Peaks 1 - 2d post-injury → Returns to RR within 1 - 3w

• Ongoing injury → Persistent marked ALT increase

-ve: None (different DDx for liver injury)

DDx:

• Marked increase (>10x RR) → 1˚ Liver disease

• Variable increase → Endocrinopathy, pancreatitis, anaemia/dehydration/cardiac disease, drugs, hepatic neoplasia (extensive)

• No change/mild increase → Chronic liver failure OR incidental in older animals

AST

Function: NON-liver specific leakage enzyme used as an indicator of hepatocellular OR muscle injury/necrosis in large animals (also dogs and cats)

Lifespan: Half-life shorter than ALT and GLDH (returns to normal faster after liver injury)

-ve: Requires CK and PCV to exclude non-hepatic causes of AST increase (i.e. muscle damage or haemolysis respectively)

DDx:

1. Liver damage

2. Cardiac/skeletal muscle damage

   • Interpret with clinical signs as AST has longer half-life than CK (may have normal CK but elevated AST with muscle injury → Days since injury)

3. Haemolysis

GLDH

Function: Liver-specific leakage enzyme used in large animals as an indicator of acute hepatocellular injury/death

• Large animal version of ALT in small animals

• SDH in USA

Creatinine vs. creatine kinase (CK)

Creatinine

• Creatinine produced at constant rate by muscles and excreted by kidneys

• Less muscle mass = Less creatinine

• Increases as part of azotaemia

• Does NOT indicate muscle necrosis

Creatine Kinase

• Large enzymes in muscle cells → Requires damage to cell membrane for leakage into serum

• Does NOT change with weight loss/ill-thrift as muscle breakdown for energy is orderly process without cell membrane damage

Induction Enzymes = ALP and GGT

• Function

• Lifespan

• Disadvantage

• DDx for elevation

ALP

Function: NON-liver specific induction enzyme used in dogs and cats to indicate cholestasis

• NOT useful in large animals

Lifespan: Takes 1 - 2d to increase post-damage

• Dogs = Long half-life ~3d → Peaks 3 - 4w after and returns to normal within months

• Cats = Less sensitive and shorter half-life ~6hr

• Any increase is usually significant in cats

-ve: Complex interpretation (esp. dogs) due to many different causes of increased ALP which is typically not specific to the isoform on routine biochemistry

• Tests to separate the different isoforms are not routinely available in NZ

DDx:

1. Hepatic (cholestasis) isoform

   1. Cholestasis (eg. cholangitis and cholangiohepatitis)

   2. Feline hyperthyroidism (hepatic and bone ALP isoform + ALT)

   3. Diabetes mellitus

   4. Liver disease causing hepatocellular swelling → Increased ALT and ALP (due to 2˚ biliary obstruction)

2. Bone isoform

   1. Normal young and rapidly growing animals → Increased osteoblast activity associated with bone growth) + mild increase in calcium and phosphorus

   2. Bone diseases → Increased osteoblastic/osteoclastic activity eg. osteosarcoma, healing fractures and fibrous osteodystrophy

3. Corticosteroid and other drug-induced ALP isoforms

   1. Cushing's disease

   2. Chronic stress

   3. Iatrogenic

   4. Various anti-seizure and anaesthetic drugs → Marked ALP elevations in dogs 12 - 24hr after

GGT

Function: Liver-specific induction enzyme previously used in large animals over ALP

• Increasing use in cats and dogs in addition to ALP

• Cats = GGT used in combination with ALP to give more information about likely disease process

  • Increased GGT in cats more specific for cholangitis and ALP more specific for hepatic lipidosis

DDx: 3 C's

1. Cholestasis

   • SA: Cholangitis/cholangiohepatitis

   • LA: Recent FE, fascioliasis, ragwort toxicity

2. Corticosteroids

3. Colostrum intake in neonates (except horses and cats)

Hepatic ALP vs. bilirubin in dogs vs. cats

Dogs: Hepatic ALP increases BEFORE increased bilirubin

Cats: Hepatic ALP increases AFTER increased bilirubin

• Hepatic ALP has much shorter half-life in cats (6hr vs. 3 days in dogs)

• Any hepatic ALP increase in cats is significant

Liver Function Tests

• Function

• 2 Types (+ examples)

Function: Evaluate liver's capacity to perform functions unique to liver (vs. enzyme tests)

• Liver function can be abnormal despite maintenance of hepatocyte membranes (i.e. normal liver enzyme activity)

Types:

Substances in Serum REMOVED by Liver

1. Bilirubin

2. Bile acids

3. Ammonia → Increased with liver dysfunction

Substances in Serum MADE by Liver

1. Albumin

2. Urea

3. Cholesterol*

4. Glucose*

5. Coagulation factors

*Unreliable decrease

Are all hyperbilirubinaemia cases jaundiced?

NO >50µmol/L required for clinical signs

Describe FIVE Mechanisms of Hyperbilirubinaemia

• Signalment

• Pathogenesis

• Magnitude

• DDx

1. Fasting

   • Signalment: Horses

     • Smaller increases in cattle, pigs and cats (not dogs)

   • Pathogenesis: Fat mobilisation interferes with bilirubin uptake by hepatocytes → Increase in unconjugated bilirubin

   • Magnitude: Mild

   • DDx: Anorexia

2. Pre-hepatic (Haemolytic) Hyperbilirubinaemia

   • Signalment: ALL species (#1 in ruminants)

   • Pathogenesis: Acute haemolytic disease → Rapid Hb breakdown → Rate of bilirubin formation > hepatocyte capacity to conjugate and excrete bilirubin

   • Magnitude: Marked

   • DDx: IMHA, Leptospirosis in calves/lambs, Theileriosis, Cu/Zn toxicity

3. Hepatic Hyperbilirubinaemia

   • Signalment: ALL species

   • Pathogenesis: Extensive acute/chronic liver damage → Decreased functional hepatic mass → Impaired uptake and conjunction of bilirubin

   • Magnitude: Mild

   • DDx: FIP, liver failure

4. Post-hepatic (Cholestatic) Hyperbilirubinaemia

   • Signalment: ALL species

   • Pathogenesis: Cholestasis → Regurgitation of bilirubin into circulation

   • Magnitude: Marked

   • DDx:

     • Extra-hepatic: Obstruction in large bile ducts

     • Intra-hepatic: Obstruction in bile canaliculi between hepatocytes (hepatocellular swelling)

5. Sepsis-Associated

   • Signalment: Dog and cat

   • Pathogenesis: Increased inflammatory mediators (esp. endotoxin) → Fewer transport proteins for bilirubin → Decreased bilirubin excretion

   • DDx: E. coli pneumonia, peritonitis, endocarditis, FIP

Bilirubinuria

Conjugated bilirubin is water-soluble → Freely filtered by glomeruli into urine (detected grossly or with dipstick)

Fill out the following table

	RBCs	WBCs	Leakage enzymes	Induction enzymes	Other signs
Fasting
Haemolytic
Hepatic
Cholestasis
Sepsis

	RBCs	WBCs	Leakage enzymes	Induction enzymes	Other signs
Fasting	WNL	WNL	WNL	WNL	Follows anorexia and variable jaundice
Haemolytic	Regenerative/pre-regenerative anaemia TPP WNL	Variable (WNL/stress/inflammation)	WNL (or mild increase if hypoxia)	WNL (or mild increase with hypoxia)	Jaundice ± Other signs of haemolysis
Hepatic	WNL (or non-regenerative if chronic)	Variable (WNL/stress/inflammation)	Often increased (can be WNL if chronic)	WNL (or increased if also cholestasis)	Variable
Cholestasis	WNL (or non-regenerative anaemia if chronic)	Variable (WNL/stress/inflammation)	WNL (or increased if hepatocyte damage too)	Increased	± Bilirubinuria Jaundice common
Sepsis	WNL or relative erythrocytosis (dehydration)	Inflammatory leukogram	WNL (unless liver involved)	WNL unless liver involved	Very sick animal ± pyrexia

Bile Acids

• Normal production and recycling

• 2 Mechanisms of increased serum bile acids (+ DDx)

Normal:

1. Bile acid synthesised and conjugated in liver from cholesterol

2. → Excreted in bile

3. → 95% resorbed in intestine

4. → Enterohepatic recirculation into portal vein

5. → Liver for removal from blood and recycling to make more bile

Increased BA:

1. Decreased clearance of BA from portal blood

   1. Moderate/severe reduction in functional liver mass

   2. Portosystemic shunts (blood and bile acid bypass liver and end up in peripheral blood)

2. Decreased excretion of bile acids = Cholestasis → Returns bile acids to serum due to regurgitation into peripheral blood

Measuring Bile Acids

• Function

• 3 Disadvantages

• Sampling requirements

• Interpretation of results

Function: Increased serum bile acids indicate liver disease and decreased hepatobiliary function

Most useful when liver disease is suspected but routine biochemistry is equivocal eg.

1. Increased ALP but normal bilirubin

2. Increased bilirubin but normal ALP

3. Normal liver enzymes but other liver signs (eg. hepatic encephalopathy)

-ve:

1. NOT useful with jaundiced animals if have already ruled out non-hepatobiliary causes (i.e. haemolytic and sepsis-associated hyperbilirubinaemia ruled out)

2. Does NOT indicate cause or severity of disease (requires further testing eg. U/S or biopsy)

3. NOT routine and must be specifically requested (red top tube)

Sampling: TWO serum samples → Higher Sn and Sp

• 1st sample (baseline pre-prandial) collected 12hr post-fasting

• 2nd sample (post-prandial) collected 2hr after protein- and fat-containing meal

Interpretation:

• Normal liver = Pre-prandial → LOW bile acids and post-prandial → MILD increase in bile acids

• Damaged liver/PSS/cholestasis = Pre-prandial → Increased bile acids and post-prandial → MARKED increase in bile acids

Hypoalbuminaemia with Liver Failure

• Pathogenesis

• Chronicity

• Exception

• 2 Other laboratory features

Pathogenesis: Liver failure/hepatic insufficiency → Liver cannot make enough albumin → Hypoalbuminaemia

Chronicity: Because albumin has a long half-life (7 - 10d) hypoalbuminaemia ONLY occurs with chronic or chronic-active liver failure as must turnover existing albumin in blood

Exception: Horses (may be seen with acute hepatic disease instead)

Other Features:

1. Decreased A:G ratio (hyperglobulinaemia)

   • Portal blood from gut to liver brings in Ag from intestine → Not processed by liver → More Ag in systemic circulation → More Ag presentation in systemic circulation → Hyperglobulinaemia

2. Hypocalcaemia 2˚ to hypoalbuminaemia

   • No clinical signs (does not affect ionised calcium which controls membrane potentials)

Urea in Liver Failure

• Normal production

• Pathogenesis

• Other laboratory feature

Normal:

1. Toxic NH3 produced by breakdown of dietary protein/amino acids by GIT bacteria →

2. Absorbed into portal circulation →

3. Removed by liver through conversion to less toxic urea →

4. Urea excreted into systemic circulation →

5. Kidney removes urea in urine

Pathogenesis: Impaired hepatic function → Liver cannot convert ammonia to urea → Increased blood ammonia + decreased blood urea

• Ammonia difficult to measure

Other Feature: Ammonium biurate crystals = Brown-yellow spherical bodies with irregular protrusions (aka. thorn-apples) in urine

• Esp. with portosystemic shunts

• Normal in Dalmatians and bulldogs

Cholesterol in Liver Failure

• Normal production

• Pathogenesis

• 5 DDx for hypercholesterolaemia

• Disadvantage

Normal: Synthesised in liver → Converted to bile acids → Excreted in bile

Pathogenesis: Impaired hepatic function → Decreased cholesterol synthesis → Hypocholesterolaemia

DDx:

1. Cholestasis

2. Post-prandial (use fasting sample)

3. Altered fat metabolism (eg. pancreatitis)

4. Nephrotic syndrome

5. Endocrine diseases (hypothyroidism, diabetes and Cushing's)

-ve: VARIABLE hypocholesterolaemia

• Biliary excretion is ALSO reduced with liver failure → Normal cholesterol may be seen (± hypercholesterolaemia) depending on balance between synthesis and output of cholesterol

• Hypocholesterolaemia is supportive evidence of liver failure but does NOT change diagnostic process if normal

Main disadvantage of glucose testing for liver failure

VARIABLE glucose levels (hypoglycaemic/hyperglycaemic/normoglycaemic)

• Hypoglycaemia due to decreased hepatic gluconeogenesis and glycogen breakdown

• Hyperglycaemia due to decreased glucose uptake by liver post-eating → Interpret in context of case

Effect of liver failure on coagulation factors

Significant hepatic dysfunction → Decreased production of clotting factors → Defective 2˚ haemostasis pathway → ± Unexpected bleeding

Clinical pathology findings of liver failure are similar to what haemostasis defect? How to distinguish?

VitK antagonism (i.e. rat bait toxicity)

• Distinguish with history as liver failure = CHRONIC non-specific findings vs. rat bait = 3d onset post-toxin ingestion

EXAMPLE: “FITZ”

• Signalment: 7yr Flat Coat Retriever dog

• History: Weight loss over several months and occasional “weird episodes” with disorientation and restlessness

• PE: BCS 2/9

Interpretation:

• RBCs: Mild normocytic (normal MCV) and normochromic (normal MCHC) anaemia (low Hb, HCT and RBC). Given that MCV and MCHC are normal (and reticulocytes have not increased), the bone marrow has yet to respond to the anaemia with regeneration. This may be a pre-regenerative OR non-regenerative response. Given the chronic history of weight loss over several months, I am leaning more towards a non-regenerative response due to chronic illness. Furthermore, there is no evidence of haemolysis or haemorrhage in the history to indicate a pre-regenerative response. We can definitively rule out a pre-regenerative anaemia with blood sample in 3 - 5 days.

• WBCs: Mild eosinopenia. Given the mild nature, this is likely an insignificant finding.

• Calcium: Moderate hypocalcaemia likely due to the moderate hypoalbuminaemia. Because ~40% of calcium is bound to albumin, any decrease in albumin results in a decrease in serum calcium.

• Mild increase in ALP: Hepatic isoform increase most likely but significance not certain (cholestasis vs. mild and insignificant increase)

  • DDx:

    1. Insignificant → May be insignificant as close to RR

    2. Cholestasis

    3. Steroid isoform → No history of steroid administration and no stress leukogram

    4. Bone isoform → Ruled out on history as not a young and growing animal AND no evidence of lameness indicating bone pathology

• Mild decrease in urea: Given the non-specific clinical signs, low urea may be due to liver disease and reduced liver functional mass → Reduction in production in liver. The liver cannot take up NH3 for conversion into urea, resulting in mild reduced urea. NOT impaired renal function as typically urea is high.

  • MAY indicate starvation, but not consistent with history

• Proteins: Moderate hypoalbuminaemia with mild hyperglobulinaemia (with low A:G ratio). This evidence supports liver disease and dysfunction. The liver cannot synthesise albumin as normal resulting in a hypoalbuminaemia and concurrent hyperglobulinaemia (may be due to reduced Ag processing in the liver resulting in increased Ag presentation in systemic circulation).

  • Unlikely blood loss or decreased protein intake, protein-losing nephropathy or enteropathy as not indicated in history and would expect concurrent hypoglobulinaemia

  • Hyperglobulinaemia due to inflammation/antigenic stimulation

    • Neoplasia → Spinal pain associated with myeloma

    • Dehydration → Would expect concurrent increase in creatinine (pre-renal azotaemia)

• NORMAL leakage enzymes → Chronic liver damage = Fewer hepatocytes secreting enzymes

DDx: Evidence of significant liver disease (likely failure) and dysfunction

1. Canine chronic hepatitis

Diagnostic Steps:

1. Bile acids due to equivocal results → Confirms liver disease and reduced hepatobiliary function

   • High pre- and post-prandial bile acids → Consistent with liver disease

2. Abdominal U/S ± liver sampling

3 Disadvantages of liver biopsy

1. Cost and time (~3 days for results)

2. Risk to patient (GA required in sick animals)

3. Haemorrhage (esp. with depleted coagulation factors as with liver failure)

What is this?

• Signalment

• Gross appearance

• Histology

• Significance

Nodular Hyperplasia (5)

Signalment: Older animals (esp. dogs)

Appearance: Single/multiple firm, spherical nodules projecting from liver surface and extending into the parenchyma

• Often slightly paler than rest of liver (accumulate fat and glycogen) → Mistaken for neoplasia

Histology: Normal

Significance: NONE

What is this?

• Signalment

• Gross appearance

• Significance

• 2 DDx (+ how to differentiate)

Telangiectasis (3)

Signalment: Cattle and older cats

Appearance: Multiple dark red circumscribed spots = blood-filled cavities (dilated sinusoids)

Significance: NONE

DDx:

1. Haemangiosarcoma metastasis = Raised with compressive mass effect (assess 1˚ masses in spleen)

2. Petechiae = Smaller than telangiectasis

2 Reasons why the liver undergoes rapid PM decomposition

1. Abundant nutrient content

2. Close proximity to GIT bacteria

Label the following images

1. Putrefaction = Irregular pale, soft and stinky foci ± gas bubbles on capsular surface (may extend into parenchyma)

2. Autolysis = Diffuse softening of liver → Putty (partly due to bacterial action)

3. Pseudomelanosis = Green-black pigmentation of tissues in contact with GIT (typically only confined to outside and caudal aspects of liver)

4. Bile imbibition = Yellow-brown staining of tissues in contact with gallbladder (or bile ducts)

5. Putrefaction (tight liver full of gas)

6. Pseudomelanosis

7. Bile imbibition

8. Haemoglobin imbibition = Red-staining of blood vessel endothelium and adjacent liver

2 Causes of passive hepatic congestion (+ which is most common)

1. Right-sided heart disease #1 (CHF, right AV endocardiosis or endocarditis etc.)

2. Partial blockage of hepatic vein/caudal vena cava due to thromboembolism, abscess (eg. caval syndrome) or neoplasia

What is this?

Appearance

Acute Passive Hepatic Congestion

Appearance:

1. Diffusely enlarged and dark red colouration

2. Abundant blood ooze on incision

3. Central veins and centrilobular sinusoids distended by dark blood ± Enhanced lobular pattern when cut (mottled) but NOT nutmeg liver

What is this?

Appearance

Chronic Passive Hepatic Congestion eg. RCHF → Nutmeg liver = Enhanced lobular pattern with dark red centrilobular areas contrasting starkly with pale periportal areas

1. Rounded lobe margins

2. Centrilobular regions (veins and sinusoids) remain congested and dark red (filled with poorly oxygenated blood)

   • Persistently hypoxic hepatocytes in centrilobular region degenerate and die

3. Periportal hepatocytes undergo swelling and degeneration → Pale (less affected by hypoxia)

What is this?

Appearance

Very Chronic Passive Hepatic Congestion

1. Increased fibrosis = White and firm areas replacing dead hepatocytes

2. Cardiac fibrosis = Thickened capsule

3. Purple tinge to liver (deoxygenated blood is more purple than normal due to cardiac fibrosis)

Effects of ACUTE/SEVERE anaemia on the liver

Degeneration and death of centrilobular hepatocytes (centrilobular regions receive oxygenated blood last)

• MARKED PCV decrease (chronic anaemia can be compensated) and mild increase in leakage liver enzymes as 2˚ liver disease

• eg. Severe haemorrhage, IMHA, Theileriosis

Portosystemic Shunt (3)

• Definition

• 2 Effects

• Gross appearance

• 2 Anatomic types (+ signalment)

• 2 Aetiologies

• Diagnosis

Definition: Abnormal vascular connection between portal vein and systemic circulation allowing blood from GIT to bypass the liver → Shunted back to systemic circulation via the caudal vein (occasionally azygous vein or hepatic vein)

Effects:

1. Liver does not receive nutrients and factors necessary for growth and function → Atrophy

2. Decreased liver function (eg. hepatic encephalopathy and oedema) and cannot recycle bile

Anatomic Types:

1. Extrahepatic = Most abnormal vascular connection sits OUTSIDE liver (cats and small breed dogs eg. Yorkies)

2. Intrahepatic = Most abnormal vascular connection running WITHIN liver (large breed dogs eg. ductus venosus)

Aetiologies:

1. Congenital PSS = Juvenile dogs (also cats esp. Birmans)

2. Acquired PSS = ALL species but older dogs #1

Diagnosis:

1. Bile acid serum concentration pre- and post-prandial to assess liver function (equivocal liver enzyme results) → PSS = Marked pre- AND post-prandial bile acid concentration

2. Definitive diagnosis with imaging (eg. portography, scintigraphy or CT) to ID abnormal vessels between portal and systemic circulation

Congenital PSS

• Appearance

• Aetiopathogenesis

• 3 Clinical signs

Appearance:

1. Single abnormal vascular connection (difficult to locate at PM)

2. Microhepatica (otherwise normal shape and consistency)

Aetiopathogenesis: Failure of ductus venosus to close after birth OR microvascular dysplasia

Clinical Signs:

1. Poor growth (thin and small for age)

2. ± Neurological signs due to hepatic encephalopathy

3. ± Late stage ascites (uncommon) due to end-stage hypoalbuminaemia (NOT portal hypertension)

Acquired PSS

• Appearance

• Aetiopathogenesis

• 3 Clinical signs

Appearance:

1. Number of tortuous abnormal vascular connections in mesentery (easier to locate at PM)

2. Portal vein distension

3. Small, firm and fibrotic liver

Aetiopathogenesis:

1. Chronic severe liver disease

2. Remodelling and fibrosis compresses blood vessels (eg. canine chronic hepatitis)

3. 2˚ to portal hypertension due to chronic liver disease/vascular obstruction

4. Portal blood cannot pass through liver

5. → Creates escape valve to allow itself back into systemic circulation

Clinical Signs:

1. Ascites common and EARLY in clinical course (due to portal hypertension NOT liver failure and hypoalbuminaemia)

2. ± Neurological signs

Clinical Pathology Findings of PSS

1. Liver enzymes

2. Bile acids

3. Bilirubin

4. Liver function markers

5. Urinalysis

6. RBCs

7. Creatinine

1. Liver enzymes (ALT, AST and ALP) mildly increased/normal as chronic process and fewer hepatocytes in a small liver

2. Bile acids markedly increased (BOTH pre- and post-prandial)

3. Increased bilirubin (acquired PSS)

4. ± Signs of liver failure depending on severity and stage (decreased albumin, urea, glucose, cholesterol + increased PT/APTT)

5. ± Ammonium biurate crystalluria (thorn apples)

6. ± Mild microcytic non-regenerative anaemia (not well-understood)

7. Low creatinine due to low muscle mass

What is this?

• Gross appearance

• Clinical signs

• 4 Risk factors

• 4 Diseases

Hepatic Lipidosis (3)

Appearance: Excess lipids in liver due to altered fat metabolism

1. Enlarged (rounded lobe margins)

2. Diffusely pale (red-pink → orange-yellow)

3. Soft, greasy and friable (may float in water due to high fat content)

Clinical Signs: Liver disease/failure when severe

Risks:

1. Obesity

2. Starvation

3. Pregnancy

4. Lactation

DDx:

1. Ketosis

2. Diabetes mellitus

3. Feline fatty liver syndrome

4. Equine hyperlipaemia

Ketosis

• 2 Signalments

• Clinical signs

• Pathogenesis

• 2 Diagnostic tests

Signalment:

1. Multiple-bearing ewes in late gestation (aka. pregnancy toxaemia)

2. Dairy cattle post-partum and early lactation

Clinical Signs: Weak + recumbent → Death ± ketone (onion) smell on PM

Pathogenesis:

1. Insufficient glucose precursors in diet to meet high metabolic demand

2. Negative energy balance

3. Markedly increased fat mobilisation from adipose tissue to compensate

4. Hepatic lipidosis and increased ketone production

Diagnosis:

1. Elevated ketones = β-hydroxybutyrate (BOH) measured on serum biochemistry or urine dipstick or milk

2. Hypoglycaemia

Feline Fatty Liver Syndrome

• Signalment and pathogenesis

• 3 Clinical signs

Signalment: Obese cats that become anorexic for a short period of time (eg. illness or go missing for several days)

Clinical signs: Hepatic failure with encephalopathy and jaundice ± death

Equine Hyperlipidaemia

• Signalment

• Gross appearance

Signalment: Overweight OR lactating mare ponies (esp. Shetland), miniature horses and donkeys following period of anorexia

Appearance: Markedly fatty and friable liver that often ruptures while alive

What is this?

• Aetiology

• 2 Example DDx

• Gross appearance

Glycogen Accumulation (3)

Aetiology: Excessive glycogen accumulation in liver due to metabolic diseases altering glucose metabolism Insulin and corticosteroids help convert glucose → glycogen

DDx:

1. Diabetes mellitus in cats and dogs (lipids AND glycogen present in liver)

2. Hyperadrenocorticism in dogs (endogenous OR exogenous) as steroids induce glycogen synthase activity

Appearance: Diffuse/patchy swelling and pallor (difficult to distinguish from mild hepatic lipidosis)

EXAMPLE: “LOKI”

• Signalment: 9m castrated Cairn Terrier

• Clinical Signs: Poor growth, lethargy, progressive anorexia and occasional head pressing against wall AND vomiting

  • BCS 2/9 with pale pink gums

Interpretation:

• There is a mild microcytic (low MCV) and normochromic (normal MCHC) non-regenerative or pre-regenerative (normal retics., MCV and MHCH) anaemia (low Hb, PCV and RBC). This may be a pre-regenerative OR non-regenerative response. Given the chronic history of poor growth, I am leaning more towards a non-regenerative response due to chronic disease. Low MCV is highly indicative of abnormal Fe metabolism potentially due to congenital PSS. Potentially also young age is a contributing factor (young animals have lower RBC values). Furthermore, there is no evidence of haemolysis or haemorrhage in the history to indicate a pre-regenerative response. We can definitively rule out a pre-regenerative anaemia with blood sample in 3 - 5 days.

  • Bone marrow disease = Expect other WBC changes

• There is a mild leukocytosis (high WBCs) characterised by a mild mature neutrophilia (high neuts. and normal bands), lymphopenia (low lymphocytes) and monocytosis (high monocytes). This is most consistent with a stress leukogram and elevated corticosteroids due to being ill.

• Given that there are many platelet clumps present on blood smear and numbers appear adequate, the mild thrombocytopenia (low platelets) is most likely an artefactual change (eg. traumatic venipuncture activating platelets and causing them to clump).

• There is a mild decrease in urea. Given the non-specific clinical signs, low urea may be due to liver disease and reduced liver functional mass → Reduction in production in liver. The liver cannot take up NH3 for conversion into urea, resulting in mild reduced urea.

• There is a mild decrease in creatinine. Normal production of creatinine occurs at a fairly constant rate and depends on the patient’s muscle mass. Given that Loki’s BCS is 2/9, he likely has poor muscle mass which is causing the reduction in creatinine.

• Liver enzymes (AST, ALT and ALP) are normal, but the high end of the reference range. This makes an acute liver pathology unlikely, however, we cannot rule out a chronic disease process. This is because a cirrhotic or smaller liver has very few functioning hepatocytes to produce an expected elevation in liver enzymes. Not only is this consistent with the chronic history, but the changes in liver function tests (i.e. bilirubin, cholesterol and albumin) too.

• A mild hyperbilirubinaemia (high bilirubin) could be due to one of five mechanisms:

  1. Fasting = Unlikely given this is a dog (more common in horses)

  2. Haemolysis = Unlikely given the mild nature of the hyperbilirubinaemia and normal RBCs on blood smear examination

  3. Hepatic disease = Most likely given the other biochemistry changes indicating reduced liver function

  4. Cholestasis = Unlikely as induction enzyme (ALP) is normal

  5. Sepsis = Lack of inflammatory leukogram rules out cause of hyperbilirubinaemia

• There is a mild hypocholesterolaemia (low cholesterol) and mild hypoalbuminaemia (low albumin) with a moderately low A:G ratio. These changes are most likely due to impaired hepatic function and loss of significant liver mass (liver normally synthesises cholesterol and albumin) resulting in reduced circulation of these substances.

• The mild hypocalcaemia (low calcium) is likely due to the hypoalbuminaemia. Because ~40% of calcium is bound to albumin, any decrease in albumin results in a decrease in serum calcium.

DDx: Congenital portosystemic shunt (most likely extrahepatic given small breed)

Pathogenesis of head pressing:

1. Ammonia produced from protein breakdown and microbial digestion in the large intestine

2. Ammonia absorbed into bloodstream through GIT → Portal vein

3. Congenital microvascular dysplasia → Blood vessels from portal vein bypass the liver straight into systemic circulation (eg. into caudal vena cava)

4. Ammonia and other toxins enter systemic circulation (cannot be converted to non-toxic urea for elimination)

5. Toxins travel to brain and cross BBB causing hepatic encephalopathy

6. Clinical signs of CNS dysfunction result (eg. head pressing, depression, seizures, altered behaviour and mentation)

Diagnostic tests:

1. Bile acid serum concentration pre- and post-prandial to assess liver function (equivocal liver enzyme results) → PSS = Marked pre- AND post-prandial bile acid concentration

2. Imaging for definitive diagnosis of PSS to ID the abnormal vessels between portal and systemic circulation (eg. scintigraphy)

4 DDx for pale liver on PM

1. Glycogen = Tan and large

2. Autolysis = Normal sized liver

3. Putrefaction = Rotten with gas bubbles

4. Lipid = Orange/yellow and large

What are the following causes of the liver FNAs?

A = Normal liver FNA (lipofuscin granules = Normal aging change)

B = Neutrophilic hepatitis

C = Hepatic lipidosis (lipid packed within cytoplasmic vacuole)

D = Autolysis (vacuolation OUTSIDE hepatocytes)

3 Portals of bacterial entry into the liver (+ examples)

1. Blood (eg. portal vein, hepatic artery, umbilical veins in neonatal calves or lambs) #1 most common

2. Biliary system = Biliary stasis → Ascending infection from bile ducts (eg. due to inflammation or obstruction as in suppurative cholangiohepatitis in dogs and cats)

3. Direct extension of inflammatory process from tissues adjacent to liver (eg. reticulum in hardware disease in cattle)

Gross appearance of hepatitis due to septicaemia

Highly variable manifestation of bacterial infection which depends on:

1. Bacterial species

2. Host species

→ Cannot ID specific bacteria from gross appearance

3 Different presentations of bacterial liver infections due to septicaemia (+ bacterial agent examples)

1. Multifocal tiny white spots randomly scattered throughout the parenchyma = Tiny multifocal areas of hepatic inflammation and necrosis (eg. Yersinia in lambs)

2. No gross features (eg. Salmonella spp. or Actinobacillus equuli in neonatal foals)

3. Large, single/multiple, well-demarcated lesions = Often incidental due to walling off of infection (eg. Abscess = Trueperella pyogenes, granuloma = Mycobacteria spp., coagulative necrosis = Fusobacterium necrophorum)

Liver Abscesses in the Neonatal Period (3)

• Signalment

• Pathogenesis

• 3 Agents

• Prognosis

• 3 Methods of diagnosis

Signalment: Calves, lambs ± foals in first 2 - 6 weeks of life

Pathogenesis:

1. Inadequate colostrum intake in first 24hr → Lack of maternal antibody → Immunosuppression

2. Predisposes to umbilical infection (or GIT)

3. Septicaemia

4. Liver abscessation (also lungs, spine, brain and joints)

Agents: Mixed environmental contaminants

1. Fusobacterium necrophorum → Multifocal areas of green-yellow coagulative necrosis

2. Trueperella pyogenes → Classic abscessation

3. E. coli

Prognosis: Fatal

Diagnosis: Culture is NOT useful as it only shows a mixed environmental bacterial infection

1. Signalment (neonatal lamb/calf with history of dubious colostrum intake)

2. Gross lesions at PM

3. High GGT → Indicates adequate colostrum intake (GGT activity in mammary glands)

Signalment of liver abscesses in older animals (+ significance)

Cattle #1 → Incidental findings at PM as infection is wall off and large functional reserve

Pathogenesis of pulmonary embolic aneurysm in cattle

1. Invasion and rupture of hepatic abscess into hepatic vein or caudal vena cava

2. → Dissemination of bacterial embolic around the body in the blood

3. Septic emboli cause 2˚ lesions in various organs (eg. vegetative valvular endocarditis and lung abscesses)

4. Bacterial proliferations within lung abscesses → Invasions of pulmonary vessels = Pulmonary embolic aneurysm

5. Pneumonia, vessel rupture, haemoptysis and epistasis

6. → Sudden death

Overview of Leptospirosis

• Source

• Portal of entry

• TWO syndromes

  • Agent

  • Signalment

  • Clinical signs

Source: Infected animals intermittently shed leptospires in urine → Infection from contaminated water sources (eg. rat urine after floods)

Portal of entry: MM and damage skin

Syndromes:

1. Acute intravascular haemolytic anaemia

   • Agent: Pomona

   • Signalment: Young calves, lambs and fawns

   • Clinical Signs: Weak, jaundice (pre-hepatic), anaemia, redwater

     • No haemolytic anaemia in adults

2. Acute concurrent severe renal and liver injury

   • Agent: Copenhageni (also Pomona, Hardjo, Tarassovi)

   • Signalment: Dog of ANY age

   • Clinical Signs: Lethargy, anorexia, fever, vomiting, abdominal pain, jaundice → High mortality or liver failure later

What is the main DDx for dog presenting with severe renal and/or liver disease?

Leptospirosis

Fill out the following table for Leptospirosis syndromes

	Young calf/lamb	Dog/puppy
Syndrome
RBC changes
WBC changes
Urine
Jaundice (+ bilirubinaemia)
Azotaemia
Leakage enzymes
Induction enzymes
Other

	Young calf/lamb	Dog/puppy
Syndrome	Haemolysis	Renal and liver damage (either OR both)
RBC changes	Regenerative anaemia with normal TPP	No
WBC changes	Variable - MAY seen inflammatory leukogram	Often inflammatory leukogram (neutrophilia with left shift and toxic changes)
Urine	Red due to haemoglobinuria	Variable, but not red
Jaundice (+ bilirubinaemia)	Yes = Haemolytic jaundice (pre-hepatic)	Yes = Hepatic/cholestatic ± sepsis associated jaundice
Azotaemia	None	Significant azotaemia ± Increased phosphorus (AKI)
Leakage enzymes	No/mild increase in GLDH 2˚ to anaemia	Marked increase in ALT and AST
Induction enzymes	No/mild increase in GGT 2˚ to anaemia	Marked increase in ALP
Other	Multiple animals usually affected with weakness, lethargy ± death	Very sick with lethargy, vomiting, pyrexia, abdominal pain (kidneys) + death common

THREE methods of leptospirosis diagnosis in dogs

• Sample

• Disadvantages

1. Serology MAT Ab

   • Sample: Paired samples (red top) taken 2 - 4w apart → Significant rising titre of Ab

   • -ve:

     1. Slow turnaround = Animal dead or recovered by the time 2nd titre is obtained (treat empirically while awaiting results)

     2. Must select specific serovars

     3. Vaccination → False positives

2. PCR

   • Sample: Urine, kidney, liver ± blood (purple top) → Submit blood AND urine for PCR at the same time (Lepto goes through leptospiraemic phase in blood BEFORE being shed in urine → Test blood and urine simultaneously to increase chances of detecting it in either phase)

     1. Intermittent bacterial shedding in urine and seldom in blood

     2. Fresh kidney (most reliable) sample difficult to obtain AM

     3. Does NOT ID serovar involved

     4. Long turnaround time (treat while awaiting results)

3. PM findings and histology of liver and kidney = Definitive diagnosis

Culture is difficult

Prevention of leptospirosis in dogs + cross-protection

Vaccination containing Leptospira interrogans serovar Icterohaemorrhagiae

• Protects against Leptospira interrogans serovar Copenhageni

• Unknown cross protection against other serovars (including those that are livestock-associated)

Why must care be taken with diagnosis and treatment of leptospirosis?

ZOONOTIC! With lifelong effects → PPE: Eye protection, masks and gloves for PM or treatment

What is this? (pig liver)

• Pathogenesis

• Gross appearance

• Significance

Nematode Migration (3) = Ascaris suum → Milk spotted liver

Pathogenesis:

1. Larvae migrate through liver → Tracts of necrosis and inflammation

2. Tracts eventually replaced by small linear areas of fibrosis

3. ± Abscess and granuloma

Appearance: Multifocal pale white/pink areas of fibrosis over the liver

Significance: Clinically insignificant in many domestic species

What is this? (sheep liver)

• Pathogenesis

• Example

• Appearance

• Clinical significance

Cysticercus spp.

Pathogenesis: Larval cestodes of Taenia genus develop encysted forms within the liver of the IH

• Adults are clinically insignificant in the DH

Example: Cysticercus tenuicollis (Taenia hydatigena)

Appearance: Single small fluid-filled cysts in ruminants → Firm fibrotic nodular foci

Significance: Clinically insignificant BUT result in carcass downgrade at slaughter and indicates dog (DH) exposure to offal and defaecation on pasture

What is this? (sheep liver)

• Significance

• Hosts

• Gross appearance

Echinococcus granulosus

Significance: Zoonotic hydatid disease that has been eradicated from NZ (notify MPI if suspected)

Hosts:

• DH = Dogs

• IH = Most species (eg. sheep and people) → Cysts

Appearance: Multiple large, thick-walled fluid-filled cysts in liver ± lungs

What is this?

• Hosts

• Signalment

• Pathogenesis

• 3 Clinical pathology findings

  • GGT

  • Bilirubin

  • GLDH

• 3 Clinical signs

Fasciola hepatica

Hosts: DH = Adult sheep (less commonly cattle and goats)

• IH = Lymnaea spp. of aquatic snail (more common disease in swampy areas)

Pathogenesis:

1. Ruminants ingest infective larvae

2. Larval migration to liver → Extensive hepatic damage

3. Enter bile ducts to mature to adults

4. Early = Adults cause cholangitis and bile duct obstruction → Cholestasis

5. Chronic infection = Dilation and fibrosis of bile ducts

Appearance: Hosepipes of enlarged, thickened and firm, white fibrotic bile ducts

Clinical Pathology Findings:

1. Mild GGT increase (more mild than facial eczema)

2. ± Hyperbilirubinaemia

3. Normal GLDH

Clinical Signs: Variable severity

1. Ill-thrift

2. Anorexia

3. ± Anaemia (fluke ingest blood)

What is this? (rabbit liver)

• Pathogenesis

• Pathogenesis

• PPP

• Signalment

• 7 Clinical signs

• Gross appearance

• 3 Methods of diagnosis

Hepatic Coccidiosis in Rabbits = Eimeria steidae

Pathogenesis:

1. Naive rabbits ingest sporulated oocysts which survive for months in environment

2. Sporozoites released from the oocysts in the duodenum

3. Sporozoites invade intestinal wall to migrate to the liver via the portal vein and lymphatic vessels

4. Coccidial organisms live and reproduce in the bile duct epithelium

PPP: 15 - 18d

Signalment: Weanlings (adults = resistant)

Clinical Signs:

1. Anorexia

2. Weight loss

3. Diarrhoea/faecal staining

4. ± Hepatomegaly

5. ± Ascites

6. ± Jaundice

7. ± Sudden death

Appearance: Small multifocal white/pale yellow nodules in liver

Diagnosis:

1. Faecal flotation for oocysts (requires differentiation from intestinal infections with other types of Eimeria)

2. Impression smears of liver for oocysts = Refractile oval structures

3. Histology at PM for oocysts

2 Ways toxins cause liver damage

1. Direct hepatotoxic damage

2. Biotransformation = Liver convert substances into excreted metabolites via intermediate reactive compounds which are more hepatotoxic than the original ingested compound (eg. cytochrome P450 enzyme)

What is this?

• Seasonality

• Pathogenesis

• Signalment

• Clinical signs

• Gross appearance

• Clinical pathology findings

Chronic Facial Eczema

Seasonality: Late summer and autumn = Warm and humid conditions favour growth of Pithomyces chartarum on dead pasture litter

Pathogenesis:

1. Animal ingests fungal spores which release sporidesmin mycotoxin

2. Sporidesmin absorbed into blood, removed by liver and excreted in bile

3. → Direct bile duct damage results in cholestasis and jaundice + damage into adjacent liver parenchyma

4. Damaged liver cannot effectively excrete phytoporphyrin (phylloerythrin) from ingested green plant breakdown in GIT

5. → Retention of phytoporphyrin in blood

6. Sunlight passes through skin to activate phytoporphyrins in blood → Photosensitisation

Signalment: Older animals with sporidesmin exposure over multiple seasons

Appearance: OBVIOUS boxing-glove liver

• Atrophy and fibrosis of left lobe → Small flap of fibrotic tissue (blood from GIT hits left lobe first)

• Hypertrophy and fibrosis of right lobe → Firm and round (compensatory hypertrophy)

Clinical Pathology Findings:

1. Normal GLDH and GGT

2. Rare serum biochemical changes of liver failure (only when >70 - 80% loss)

What is this?

• Onset

• Signalment

• 3 Clinical signs

• PM findings

• 3 Clinical pathology findings

Acute/Subacute Facial Eczema

Onset: ≥10d from ingestion

Signalment: Young animals with no prior FE damage → Recent sporidesmin ingestion

Clinical Signs:

1. ± Jaundice

2. Red, wet, sloughing and painful photosensitisation (equivalent to 3rd degree burns)

3. Acute death

PM: NORMAL! ± Slightly bronze and enlarge liver (difficult to see)

Clinical Pathology Findings:

1. Markedly increased GGT (≤20 - 30x)

2. Mild/moderate increased GLDH

3. Hyperbilirubinaemia

What is this?

• Source

• Pathogenesis

• Signalment

• 4 Clinical signs (+ onset)

• PM findings

• 2 Clinical pathology findings

Source: Ragwort = #1 NZ plant containing PAs

• Acute intoxication = Rare (most plants containing PAs are unpalatable) unless animals facing complete starvation and forced to eat unpalatable toxic plants

• Chronic intoxication = Common due to repeated and seasonal intoxication

Pathogenesis: Indirect hepatotoxicity = Ingested PAs converted to hepatotoxic metabolites by CYP450 (pyrollic esters = alkalising agents that destroy cell components)

Signalment: Cattle and horses #1 (Sheep and goats more resistant to intoxication and pigs seldom exposed to ragwort)

Clinical Signs: 1 week to several months post-ingestion

1. Weight loss

2. Diarrhoea

3. Jaundice

4. Neurological signs due to hepatic encephalopathy (hyperexcitability, aimless wandering and ataxia)

PM: Cirrhosis = Small, pale and firm liver with variable interspersed nodules of regenerating liver parenchyma separated by thick fibrous bands

Clinical Pathology Findings:

1. Normal liver enzymes (GLDH and GGT)

2. ± Serum biochemical changes of liver failure (low urea, glucose, cholesterol etc.)

What is the following diagnoses?

1. Chronic FE = Markedly abnormal size, colour and shape → Left lobe atrophy and right lobe hypertrophy → Boxing glove appearance

2. Chronic ragwort = Markedly abnormal size, colour and shape → Classic cirrhosis: Smaller, paler and firmer liver with variable interspersed nodules of regenerating liver parenchyma separated by thick fibrous bands

3. Chronic liver fluke = Normal size, colour and shape → Dilations and fibrosis of bile ducts (hosepipes)

Copper Toxicity (3)

• Pathogenesis

• Signalment

• Risk factors

• 3 Causes (+ example DDx)

Pathogenesis: Hepatotoxic at high concentrations = Free radical production and oxidative damage of hepatocytes and other cells

Signalment:

1. Sheep #1 (tendency to store copper in liver and reduced ability to excrete Cu in bile)

2. Dogs (eg. Bedlington Terriers) = Hepatotoxic at high concentrations = Potential cause of canine chronic hepatitis

Risks: VitE or Mo deficiency = Cu antagonists

Causes:

1. Primary metabolic defect in copper metabolism

   • eg. Autosomal recessive mutation in Cu transport proteins (COMMD1) → Accumulation of excess Cu in hepatocytes

   • Signalment: Bedlington Terriers (also WHWT and Dalmatians = Familial Cu accumulation in many other dog breeds)

2. Altered hepatic biliary excretion = Sheep less able to excrete copper in bile

3. Dietary copper excess = Copper over-supplementation in sheep and cattle

Acute Copper toxicity

• Aetiology

• 5 Clinical signs (+ onset)

• PM findings

Aetiology: Ruminants after accidental administration of single large dose of oral or parenteral copper → Hepatic necrosis and acute gastroenteritis ± Concurrent Se of vitE deficiency

• Supplementation NOT voluntary intake

Clinical Signs: ≤48hr post-ingestion

1. Abdominal pain

2. Diarrhoea

3. Paralysis

4. Collapse

5. Death

PM: Grossly dark red and swollen liver (often mottled)

What is this?

• Signalment

• Pathogenesis

• 3 Clinical signs (+ onset)

• 4 PM findings

• Diagnosis

• 5 Clinical pathology findings

Chronic Copper Toxicity

Signalment: Sheep (also calves)

Pathogenesis: Acute presentation but chronic 2-step process

1. Copper accumulates in hepatocytes over weeks to months due to dietary excess (esp. low Mo or other Cu antagonists)

2. Crisis initiates sudden release of stored copper from hepatocytes (eg. hepatic damage due to ragwort ingestion, stress, transport, starvation)

3. Copper release initiates hepatic necrosis and oxidative damage of erythrocytes

4. → Acute severe haemolytic Heinz body anaemia and severe IV haemolysis

Clinical Signs: 12hr post-stressful event

1. Jaundice (haemolytic, hepatic AND post-hepatic)

2. Haemoglobinuria

3. High mortality

PM:

1. Soft, enlarged and pale orange liver

2. Dark red-black kidneys (gun metal) due to Hb oxidation to methaemoglobin

3. Jaundiced carcass

4. Red urine

Diagnosis: Fresh liver and/or kidney samples for toxicology (Cu levels)

Clinical Pathology Findings:

1. Severe regenerative and haemolytic anaemia (often still in pre-regenerative phase) = Haemolysis

2. Many Heinz bodies in RBCs = Haemolysis

3. Haemoglobinuria = Haemolysis

4. Hyperbilirubinaemia + bilirubinuria = Haemolysis AND hepatocyte damage ± post-hepatic 2˚ to hepatocellular swelling

5. Marked increase in ALL liver enzymes (GLDH and GGT in large animals) = Hepatocyte damage

Species most likely to have toxicosis from therapeutic drugs

Cats more susceptible to intoxication due to low activity of key hepatic detoxification enzyme

List 4 therapeutic drugs that can cause hepatotoxicity (+ signalment)

1. Paracetamol (aka. Panadol, acetaminophen) = ALL cats

   • Heinz body anaemia

   • Acute liver necrosis with increased ALT and ALP

Idiosyncratic drugs = SMALL number of animals due to unknown mechanisms

2. Carprofen (aka. rimadyl, vetprofen) = Occasional acute hepatic necrosis in dogs (esp. Labradors)

3. Diazepam (aka. valium) = Occasional acute hepatic necrosis in cats

4. Anticonvulsants (eg. phenobarbital, phenytoin, primadone) = Chronic hepatotoxicity, cirrhosis and chronic liver failure in some dogs on long-term therapy

List 6 other toxins causing hepatic damage

1. Xylitol

2. Metaldehyde

3. Aflatoxins (eg. Aspergillus spp.)

4. Brassicas

5. Mushrooms

6. Blue-green algae

List 2 other (orphan) hepatic diseases

1. Canine chronic hepatitis (aka. "chronic-active hepatitis") (3)

2. Liver haemorrhage and/or rupture (3)

Define canine chronic hepatitis

Non-specific diagnosis describing appearance of liver due to persistent inflammation ≥ 6 months in duration

Canine Chronic Hepatitis (3)

• Signalment

• 4 Causes

• Clinical pathology findings

  • ALT/AST

  • ALP and bilirubin

  • Liver function enzymes

  • RBCs

• Prognosis

• PM findings

• Diagnosis

Signalment: Middle-aged to older dogs

Causes: Original initiating cause often unknown an irrelevant → Unresolved inflammation

1. Inherited/familial defects of copper metabolism in Bedlington Terriers, WHWT and Dalmatians

2. Infectious canine hepatitis

3. Leptospirosis

4. Hepatotoxic drug damage

Clinical Pathology Findings:

1. Variable increase in ALT and AST → Normal with increasing chronicity

2. Increased ALP and bilirubin

3. Decreased urea, glucose, cholesterol and albumin

4. Increased coagulation times (eg. PT and APTT)

5. Increased bile acids

6. Non-regenerative anaemia of chronic disease

Prognosis: Poor due to complete liver failure within weeks or months of diagnosis

PM: Mildly small, firm nodular and fibrotic liver → Complete cirrhosis

Diagnosis: Biopsy and histology

• Cannot determine inciting cause

• Suspected copper storage abnormalities → Test liver copper levels in fresh biopsy samples

What is this?

• 2 Mechanisms (+ DDx)

• Prognosis

• PM findings

Liver Haemorrhage/Rupture

Mechanisms:

1. Normal OR foetal liver with MAJOR trauma

   1. Traumatic HBC in dogs and cats

   2. Traumatic dystocia in lambs and calves

2. Diseases causing diffuse hepatic enlargement and friability + MINOR trauma

   1. Acute hepatitis

   2. Severe congestion

   3. Hepatic lipidosis

   4. Neoplasia

PM: Torn liver capsule and underlying liver parenchyma with free abdominal fluid

Lymphocytic Cholangitis (3)

• Signalment

• Aetiology

• Pathogenesis

• Clinical signs

• PM findings

• Diagnois

• Clinical pathology findings

Signalment: Common CHRONIC disease in middle-aged to older cats

Aetiology: Unknown

Pathogenesis: Inflammatory cells (mainly lymphocytes) surround and destroy bile ducts and adjacent hepatocytes

Clinical Signs: Mild, non-specific CHRONIC clinical signs (vomiting and lethargy) and cyclical

• Jaundice UNCOMMON

PM: NORMAL liver

Diagnosis: Liver biopsy for definitive diagnosis and exclusion of other DDx with hepatocytes and lymphocytes

• May miss lesions with cytology AND cannot differentiate from small cell lymphoma

Clinical Pathology Findings:

1. Normal/mild increase in liver enzymes (ALT, AST and ALP)

2. Normal/mild increase in bilirubin Only more significant when disease progression becomes more severe

Acute (Suppurative) Cholangitis (4)

• Signalment

• Cause

• 6 Clinical signs

• PM findings

• 2 Methods of diagnosis

• 3 Clinical pathology findings

Signalment: ALL species and ages (most common in dogs and cats)

Cause: Ascending bacterial infection of biliary tree from GIT → Cholangitis ± cholangiohepatitis

• Triaditis = Pancreatitis, IBD and cholangiohepatitis seen together in cats as pancreatic duct and bile duct enter the duodenum at the same major duodenal papilla

Clinical Signs: SEVERE and ACUTE (vs. lymphocytic cholangitis)

1. Pyrexia

2. Lethargy

3. Anorexia

4. Vomiting

5. Jaundice

6. Abdominal pain

PM: Normal

Diagnosis:

1. Presumptive diagnosis with antibiotic treatment

2. FNA for cytology or biopsy (definitive diagnosis) = Large numbers of neutrophils and intralesional bacteria

Clinical Pathology Findings:

1. Increased liver enzymes (ALT, AST and ALP) but variable magnitude

2. Inflammatory leukogram

3. Hyperbilirubinaemia

Malignant Primary Neoplasms of the Liver

• 4 Defining features

• 2 DDx

Features:

1. Variable single, large and extensive mass (± effacement of organ)

2. OR multiple masses

3. Poorly demarcated

4. ± Masses in other organs if has metastasised

DDx:

1. Hepatocellular adenocarcinoma

2. Cholangiocellular adenocarcinoma

Primary Benign Neoplasms of the Liver

• 3 Defining features

• 3 DDx

Features:

1. Single (focal)

2. Well-demarcated

3. Small(ish) mass

DDx:

1. Hepatocellular adenoma

2. Cholangiocellular adenoma

3. Nodular hyperplasia (often well within liver parenchyma but difficult to distinguish on histology)

Secondary Malignant Neoplasms of the Liver

• 3 Defining features

• 2 DDx

Features:

1. Multiple masses OR

2. Diffuse organ enlargement

3. Masses in other organs

DDx:

1. HSA (spleen) = Bloody and dark red

2. LSA (creamy or diffusely pale)

CASE 1: “PRINCESS”

• Signalment: 3m Yorkshire Terrier puppy

• History: Intermittent seizures becoming more frequent. Smaller than littermates

Interpretation:

• There is a mild normocytic (normal MCV), normochromic (normal MCHC) non-regenerative or pre-regenerative (normal retics.) anaemia (low Hb and HCT). Given the chronic history of poor growth (smaller than littermates) and the lack of clinical signs suggestive of haemorrhage or haemolysis, a non-regenerative anaemia is more likely. This is most likely due to chronic disease. Young animals ALSO have physiological anaemia (RR may be taken for adult). MCV is lower end of RR which is most consistent with a portosystemic shunt (congenital aetiology fits with the age of the patient).

• There is a mild leukocytosis (high WBC) characterised by a mild, mature (normal bands) neutrophilia (high neutrophils) and a mild lymphocytosis (high lymphocytes). The mature neutrophilia is most likely physiological due to fear (fight-flight) response. This is because it is very mild in nature and the patient is very young. Increased catecholamines results in migration of mature neutrophils from the marginal to circulating pool in blood vessels. The mild lymphocytosis is most likely due to a physiological fear/excitement response as we see with the neutrophilia. It may also be due to chronic inflammation due to Ag stimulation of T cells. This may be due to congenital portosystemic shunt which is causing Ag from the gut to bypass the liver for processing. Because more Ag enter systemic circulation, there is more Ag presentation which is causing the lymphocytosis.

  • NOT a stress leukogram as we would expect a lymphopenia

  • NOT inflammation as we would expect a left shift

• Mild increase in ALT and ALP: Likely due to hepatocellular damage. Although the parameters are only mildly increased, we cannot rule out liver disease as a potential DDx as a dysfunctional liver (eg. cirrhosis or microhepatica) would not produce enough leakage enzymes or induction enzymes to cause expected elevation. Increased ALP may also be the bone isoform that is due to a growing patient

• Low urea: Most consistent with reduced functional liver mass. Because the liver is responsible for producing urea from NH3 and protein breakdown products, when there are fewer functional hepatocytes, less urea (and more ammonia) will accumulate in circulation.

• Low creatinine: Because creatinine is proportional to muscle mass, the low creatinine is most likely due to the low muscle mass of the puppy as indicated in the history of poor growth (smaller than littermates).

• Mild hypocholesterolaemia and mild hypoalbuminaemia with a low A:G ratio: This is most likely due to reduced functional liver mass which reduces production of cholesterol and albumin.

  • Albumin has long half-life and so hypoalbuminaemia indicates chronic disease process

• Mild hypocalcaemia (low calcium) is most likely due to concurrent hypoalbuminaemia. Because ~40% of calcium is bound to albumin, we often see a decrease in calcium due to reduced albumin.

• Mild hypoglycaemia: Reduced functional liver mass is the most likely cause due to reduced glycogenolysis and gluconeogenesis capabilities of the liver.

DDx: Congenital portosystemic shunt (most likely extrahepatic given the signalment = Small breed)

Urinalysis:

1. Isosthenuria due to low urea causing medullary solute washout (lack of an osmotic gradient in the medulla which is required to concentrate urine)

2. Ammonium biurate crystalluria due to elevated levels of ammonia in blood (reduced transformation to urea by the dysfunctional liver) → Thorn-apple appearance

PM: Microhepatica but otherwise normal shape and appearance

Pathogenesis of seizures:

1. Congenital portosystemic shunt allows portal blood from the GIT to bypass the liver (including NH3 produced from bacterial breakdown in the colon)

2. Reduced functional liver mass (lack of nutrients delivered)

3. Reduced urea synthesis from NH3 (product of protein breakdown)

4. NH3 accumulates in systemic circulation as it can bypass the liver for transformation to urea

5. NH3 crosses the BBB and causes neurotoxicity to the neurons

6. Seizures due to hepatic encephalopathy

Diagnosis:

1. Bile acid serum concentration pre- and post-prandial to assess liver function (equivocal liver enzyme results) → PSS = Marked pre- AND post-prandial bile acid concentration

2. Imaging for definitive diagnosis of PSS to ID the abnormal vessels between portal and systemic circulation (eg. scintigraphy) and plan surgical treatment (ligation)