Overview

• Acquired portosystemic shunts (APSS): develop subsequent to portal hypertension (PH).
• Prehepatic PH: abdominal portion of portal vein causes.
• Intrahepatic PH: presinusoidal, sinusoidal, postsinusoidal causes.
• Posthepatic PH: rostral to hepatic vein causes (includes cardiac, pericardial, major veins).

Signalment

• Most common-dogs with chronic necroinflammatory liver disease.
• Less common-dogs with ductal plate malformations (congenital hepatic fibrosis phenotype), non-cirrhotic portal hypertension, recovery from panlobular necrosis, dogs with PSVA intolerant to ligation (portal atresia).
• Cats-ductal plate malformations (DPM, congenital hepatic fibrosis [CHF] phenotype), severe CCHS (rare), or PSVA intolerant to ligation (portal atresia).
• Extrahepatic bile duct obstruction (EHBDO) >6 weeks.
• Certain disorders-have age or breed incidence (see Ductal Plate Malformations (Congenital Hepatic Fibrosis); Cirrhosis and Fibrosis of the Liver; Chronic Hepatitis).
• Breeds: DPM more common in Persians and Himalayan cat, and Boxer dogs.

Signs

• Clinical signs represent sequelae of impaired hepatic perfusion; or reduced hepatic function in chronic liver disease.
• Episodic HE-major sign, may include neurobehavioral abnormalities, blindness, PU/PD, anorexia, lethargy, vomiting; neurologic signs may localize to cerebrum, brainstem, or suggest transverse myelopathy; signs often improve with fluid therapy (e.g., dextrose and potassium supplements), broad-spectrum antibiotics, lactulose, and dietary protein restriction (see Hepatic Encephalopathy).
• Ascites-common but variable; may fluctuate.
• Hypertensive splanchnic vasculopathy-causes gastroduodenal bleeding/ulceration; may progress to perforation and septic peritonitis, life-endangering blood loss if coexistent coagulopathy; can provoke severe HE due to potent encephalogenic effect of enteric blood; causes anorexia, vomiting, diarrhea, abdominal pain, anemia, and sometimes iron deficiency.
• Urogenital-obstructive uropathy due to ammonium biurate urolithiasis: gross or microscopic hematuria; pollakiuria; dysuria.

Causes & Risk Factors

• Multiple tortuous vessels-represent vasculature interconnecting portal splanchnic and systemic venous circulations.
• Lack of valves in the portal vein-allows blood to follow “a path of least resistance.”
• Portal hypertension-results from many disease processes: importantly, diffuse hepatic fibrosis with or without cirrhosis; chronic unresolved EHBDO (>6 weeks); other causes, include portal venous thromboembolism (TE), idiopathic portal hypertension, non-cirrhotic PH (obliteration of tertiary portal venules), and hepatic sinusoidal occlusion syndrome (zone 3, level of hepatic venules, veins, or vena cava); less common, disorders impair abdominal portal venous (splanchnic segment): TE, stricture, strangulation, rare portal vein atresia (congenital malformation) and congenital or acquired hepatic AV malformation (arterialized portal circulation); see Hypertension, Portal).
• Episodic HE coincidental with meal ingestion (high protein), enteric hemorrhage (bleeding tendencies, portal vasculopathy), azotemia, alkalemia, electrolyte disturbances, blood transfusion or hemolysis, infections, and administration of certain drugs.
• Hyperammonemia and impaired metabolism of uric acid to water-soluble allantoin causes ammonium urate urolithiasis.

Differential Diagnosis

• CNS signs-infectious disorders (e.g., FIP, canine distemper, toxoplasmosis, FeLV- or FIV-related infections); toxicities (e.g., lead, mushrooms, drugs, acute hepatic failure); hydrocephalus; idiopathic epilepsy; metabolic disorders (e.g., severe hypoglycemia, hypo- or hyperkalemia, hypocalcemia, severe hypophosphatemia).
• Gastrointestinal signs-bowel obstruction; dietary indiscretion; foreign body ingestion; inflammatory bowel disease.
• Urinary tract signs-bacterial urinary tract infection; urolithiasis.
• PU/PD-disorders of urine concentration (e.g., diabetes insipidus, abnormal adrenal function, hypercalcemia, primary polydipsia, congenital or acquired renal disease).
• Causes of abdominal effusion-cardiopulmonary disorders causing right-sided heart failure; pericardial disease; primary inflammatory hepatopathies; infiltrative hepatic disease (e.g., neoplasia, amyloid); non-hepatic abdominal disorders associated with effusions (e.g., splenic torsion, visceral neoplasia, carcinomatosis); or peritonitis: chemical (e.g., bile, urine, chyle) or sepsis.

CBC/Biochemistry/Urinalysis

• CBC-microcytosis (reflects PSS or iron deficiency); mild nonregenerative anemia common; poikilocytes (cats); target cells (dogs).
• Biochemistry-low BUN, low to low normal creatinine, glucose, albumin, and cholesterol are common; variable liver enzyme activity (ALP usually high in young animals [bone isoenzyme]) and bilirubin variable; findings depend on underlying cause.
• Urinalysis-variable urine concentration; ammonium biurate crystalluria, hematuria, pyuria, and proteinuria reflect urolithiasis (mechanical trauma, inflammation or infection).

Other Laboratory Tests

• TSBA-sensitive indicator of PSS; variable pre-meal and markedly increased postprandial values (>100 µmol/L) = “shunting pattern.”
• Blood ammonia values-sensitive but inconsistent indicator of HE; samples cannot be frozen or mailed for later analysis (ammonia lability); ammonium biurate crystalluria infers high blood ammonia (evaluate 3 urine specimens, 4–8 h after eating); ammonia tolerance testing-(ammonium chloride solution) most reliable test for ammonia intolerance; caution: may induce HE.
• Coagulation tests-prolonged PT, APTT, and PIVKA reflect severity of liver dysfunction, synthetic failure, DIC, or vitamin K₁ adequacy; PIVKA useful in deciding need for supplemental vitamin K₁ treatment. Low protein C activity reflects PSS (PSVA, APSS).
• Abdominal effusion-usually pure or modified transudate; high serum:effusion albumin ratio (>1.1) substantiates provocative role of PH in effusion formation.

Imaging

Diagnostic Procedures

Pathologic Findings

• Gross-small, irregularly contoured liver with chronic liver disease (cirrhosis, fibrosis).
• Normal to large size in early venous outflow obstruction (Budd-Chiari, sinusoidal obstruction syndrome).
• Large liver lobe (remainder of liver normal to small) with intrahepatic AV malformation.
• Normal to small-DPM (CHF phenotype), non-cirrhotic PH, portal TE.
• Small liver if congenital portal atresia.
• Normal to large liver in cats with polycystic liver disease: may only have microscopic cystic structures inapparent on US; characterized microscopically as DPM.

Appropriate Health Care

Inpatient-severe signs of HE; critical care

Nursing Care

See Hepatic Encephalopathy

Diet

• Nutritional support-essential to maintain body condition for optimal management of HE; balanced, restricted-protein diet important; but diet should be optimized for that patient's tolerance-(see Hepatic Encephalopathy).
• Protein allocation titrated to response in combination with treatments ameliorating HE (see Hepatic Encephalopathy); use commercial diets formulated for liver disease or moderate renal insufficiency as diet baseline.
• Dogs: baseline diet provides 2.2–2.5 g protein/kg body weight when fed to meet energy requirements; titrate protein using 0.5 g/kg allocation additions (dairy protein or soy sources), q5–7 days until optimum level established: dairy and soy protein are best sources.
• Cats being pure carnivores require meat-derived protein.
• Parenteral nutrition-see Hepatic Encephalopathy.

Client Education

• Depends on underlying cause.
• Educate client about signs of HE and potential for ammonium biurate obstructive uropathy in males; male dogs may require pre-scrotal urethrostomy.
• Educate client how to adjust diuretics (as-needed basis) to mobilize abdominal effusion.
• Educate client how to adjust oral medications and enemas (as-needed basis) to ameliorate HE (see Hepatic Encephalopathy).

Drug(s)

• Enteric hemorrhage-associated with hypertensive splanchnic vasculopathy (diapedesis and gastroduodenal ulceration) and coagulopathy; some clinicians use prophylactic acid blockers or gastroprotectants to reduce risk; treat symptomatic animal with H₂blocker or HCl pump inhibitor (omeprazole) and sucralfate; may require blood components or DDAVP (see Coagulopathy of Liver Disease).
• Abdominal effusion-sequentially measure weight, girth, body condition; initially exercise restrict (improves renal perfusion, sodium and water elimination), dietary sodium restriction.
• Conventional diuretics-combine furosemide and spironolactone; furosemide (0.5–2 mg/kg PO q12–24h) and spironolactone (0.5–2 mg/kg PO q12h, use a single doubled dose for loading one time): dose titrations based on response q4 days; adjust using incremental 25–50% dose increase. Spironolactone: potassium sparing; less potent than furosemide. Furosemide: potassium wasting, diuresis induces RAAS response. Serum:effusion albumin ratio (>1.1) may predict response to diuretics.
• Losartan and telmisartan-angiotensin receptor blockers (ARB), selectively antagonizing angiotensin-1 receptor, bypassing intermediary activation within RAAS cascade-may improve water and sodium elimination (see Portal Hypertension; Hepatic Fibrosis and Cirrhosis).
• Vasopressin V₂ antagonists (aquaretics) may assist with management of diuretic resistant ascites. Tolvaptan: see Portal Hypertension.
• Diuretic-resistant ascites-see Portal Hypertension.
• Avoid dehydration as this can lead to HE.
• Avoid hypokalemia as this can provoke HE.

Precautions

• Remain aware of altered drug metabolism related to reduced first-pass extraction (portosystemic shunting), altered hepatic metabolism/biotransformation, and reduced protein binding (if hypoalbuminemic).
• Remain vigilant for diuretic-induced dehydration and electrolyte dysregulation that may provoke HE.

Possible Interactions

Avoid metoclopramide if using spironolactone (blocks effect); avoid NSAIDs; these may inhibit furosemide-induced diuresis, potentiates renal injury, may cause sodium accumulation.

Patient Monitoring

• Reevaluate patient's at-home demeanor and appetite as a reflection of HE.
• Monitor clinical signs, appetite, body condition, weight, abdominal girth, CBC, serum biochemistry, and urine for ammonium biurate crystalluria; TSBA not useful for sequential evaluation as these are consistently increased due to PSS and ursodeoxycholic acid (drug measured in assay) administration.
• Adjust medical management to reduce episodic HE, ammonium biurate crystalluria (potential for urolith formation), and abdominal effusion.
• Inspect patient carefully for evidence of clinical bleeding; determine need for intermittent chronic vitamin K₁ administration (parenteral route).

Prevention/Avoidance

• Early treatment of acquired liver disease and EHBDO minimizes fibrosis/remodeling.
• Cautious PSVA attenuation.

Possible Complications

• Treat underlying disorders(s).
• Enteric hemorrhage associated with hypertensive vasculopathy; may require acute intensive care: to manage hypovolemia, coagulopathy, and ensuing HE; may require surgical resection of involved gut (rare).
• Dehydration, contraction alkalosis, azotemia-complications of diuretics.
• Death-from liver failure, HE complications, lethal enteric hemorrhage, or sepsis.

Expected Course and Prognosis

• Varies with underlying cause.
• Management of chronic liver disease or hepatic fibrosis seemingly extends life.
• Animals with non-cirrhotic PH and DPM (CHF phenotype) may live >8 years if managed successfully during symptomatic illness.

Associated Conditions

• Ammonium urate urolithiasis
• Ascites
• Coagulopathy
• Hepatic encephalopathy
• Enteric bleeding/ulceration
• Obstructive uropathy

Synonym

Portovascular anastomosis

See Also

• Ascites
• Cirrhosis and Fibrosis of the Liver
• Coagulopathy of Liver Disease
• Ductal Plate Malformation (Congenital Hepatic Fibrosis)
• Hepatic Encephalopathy
• Hepatitis, Chronic
• Portal Hypertension
• Portosystemic Vascular Anomaly, Congenital

Abbreviations

• APSS = acquired portosystemic shunt
• APTT = activated partial thromboplastin time
• ARB =- angiotensin receptor blocker
• AV = arteriovenous
• CCHS = cholangitis/cholangiohepatitis syndrome
• CHF = congenital hepatic fibrosis
• DPM = ductal plate malformation
• EHBDO = extrahepatic bile duct obstruction
• HE = hepatic encephalopathy
• NSAID = nonsteroidal anti-inflammatory drugs
• PD = polydipsia
• PH = portal hypertension
• PIVKA = proteins invoked by vitamin K absence or antagonism
• PSS = portosystemic shunt
• PSVA = portosystemic vascular anomaly
• PT = prothrombin time
• PU = polyuria
• TE = thromboembolism
• TSBA = total serum bile acids

Author Sharon A. Center

Consulting Editor Sharon A. Center