Portosystemic shunts and portal hypertension

How is Portal Hypertension anatomically classified?
Provide specific examples for each category.

• Prehepatic:

  • Congenital: Portal vein atresia, Primary Hypoplasia of Portal Vein (PVH).

  • Intraluminal obstruction: Thrombus, neoplasia, stenosis.

  • Extraluminal obstruction: Neoplasia, lymph node enlargement, granuloma.

• Intrahepatic:

  • Presinusoidal: Primary hypoplasia of portal vein, chronic cholangitis, hepatic arteriovenous fistula/malformation (HAVM), schistosomiasis, nodular hyperplasia, ductal plate abnormalities (Caroli's disease, congenital hepatic fibrosis).

  • Sinusoidal: Cirrhosis, chronic hepatitis, chronic cholangiohepatitis, lobular dissecting hepatitis.

  • Postsinusoidal: Veno-occlusive disease (sinusoidal obstruction syndrome), central vein neoplasia.

• Posthepatic:

  • Heart/Pericardium: Right heart failure, pericardial tamponade, constrictive pericarditis, intracardiac neoplasia, cor triatriatum dexter.

  • Caudal Vena Cava (CVC)/Hepatic Veins: Budd-Chiari syndrome, thrombosis, vena cava syndrome, neoplasia, abscess, CVC kinking.

Explain the step-by-step hemodynamic cascade that leads to Ascites in Portal Hypertension.

1. Mechanical Obstruction: Fibrosis, regenerative nodules, and microthrombi increase intrahepatic vascular resistance (IHVR).

2. Dynamic Obstruction: Imbalance of vasoactive substances and vascular endothelial dysfunction (decreased endothelial NO, increased endothelin, angiotensin II, norepinephrine).

3. Splanchnic Vasodilation: Local accumulation of Nitric Oxide (NO) and Glucagon drives progressive splanchnic arterial vasodilation.

4. Hyperdynamic Circulation: Compensatory increase in cardiac output and decrease in peripheral vascular resistance (PVR).

5. Compensatory Failure: Decrease in effective circulating arterial volume.

6. Neurohumoral Activation: Activation of RAAS and nonosmotic ADH release leads to avid renal sodium and water retention, culminating in Ascites and Acquired Multiple Portosystemic Shunts (MAPSS).

Contrast the anatomical patterns and typical canine breed predispositions for Extrahepatic vs. Intrahepatic Congenital Portosystemic Shunts.

• Extrahepatic Shunts (EH-CPSS):

  • Anatomy: Vessel runs outside the liver parenchyma (e.g., Porto-Caval, Porto-Azygos).

  • Breeds: Small/Toy breeds — Yorkshire Terrier, Miniature Schnauzer, Maltese, Cairn Terrier, Jack Russell Terrier, Dachshund, Havanese, Shih Tzu, Pug.

• Intrahepatic Shunts (IH-CPSS):

  • Anatomy: Vessel runs through the liver parenchyma (failure of ductus venosus closure).

  • Breeds: Large/Giant breeds — Irish Wolfhound, German Shepherd Dog, Labrador Retriever, Golden Retriever, Old English Sheepdog, Australian Cattle Dog, Deerhound.

What are the clinical signs and specific physical exam findings of Congenital Portosystemic Shunts in Cats?

• Feline Breed Predispositions: Domestic Shorthair (DSH), Siamese, Himalayan, Burmese, Persian.

• Key Clinical Signs: Small stature/stunted growth, ptyalism (hypersalivation), copper-colored irises/irides (classic finding), hepatic encephalopathy, and ammonium biurate urolithiasis.

What are the core clinical signs of CPSS across systems in dogs?

• General: Small stature, unthrifty coat, listless, quiet/dull.

• Neurologic (Hepatic Encephalopathy): Head pressing, pacing, circling, amaurotic blindness, seizures, coma (often postprandial).

• Urinary: PU/PD, stranguria/hematuria secondary to ammonium biurate urolithiasis.

• Gastrointestinal: Vomiting, diarrhea, anorexia, ptyalism.

What classic abnormalities are found on CBC, Serum Chemistry, and Urinalysis in a patient with a CPSS?

• CBC: Microcytic, normochromic non-regenerative anemia; target cells/poikilocytosis.

• Serum Chemistry: Mildly increased liver enzymes (ALT, AST, ALP, GGT). Decreased liver pseudo-function markers: Low BUN, low Albumin, low Glucose, low Cholesterol. Total Bilirubin is typically normal.

• Urinalysis: Ammonium biurate crystals ("thorn-apple" morphology); low USG / Isosthenuria due to loss of medullary wash-out from low BUN.

Evaluate the utility of Liver Function Tests in diagnosing CPSS.

• Serum Bile Acids (SBA): Paired 12-hour fasting and 2-hour postprandial testing is near $100\%$ sensitive. Usually markedly elevated

• Fasting Plasma Ammonia: Elevated due to failure of hepatic clearance.

• Protein C Activity: Reduced in patients with CPSS. (Critically, Protein C is normal in most patients with simple Portal Vein Hypoplasia without shunting).

What imaging modalities are used to confirm CPSS, and which is considered the gold standard?

• Abdominal Ultrasonography: Operator-dependent; visualizes turbulence (mosaic pattern on color Doppler) or vessel entering CVC/Azygos.

• Computed Tomographic Angiography (CTA): Gold standard. Non-invasive, non-operator dependent, provides 3D vascular mapping essential for surgical planning.

What are the components of medical management for CPSS prior to or instead of surgery?

• Hepatic Encephalopathy: Moderately protein-restricted diets (high quality, highly digestible protein), Lactulose (acidifies gut, traps NH4+), oral antibiotics (Metronidazole, Neomycin, or Beta-lactams to decrease urease-producing bacteria), Levetiracetam (anti-seizure prophylaxis).

• Gastroprotective: Proton Pump Inhibitors (e.g., Omeprazole) for GI bleeding/ulceration.

• Hepatoprotectants: SAMe, Silymarin.

What surgical and interventional radiology options exist for closing CPSS?

• Extrahepatic Shunts: Gradual occlusion using an Ameroid Constrictor or Cellophane Banding (prevents acute fatal portal hypertension).

• Intrahepatic Shunts: Interventional radiology using Percutaneous Transvenous Coil Embolization (PTCE) with a vena cava stent placement.

What are the major postoperative complications following CPSS attenuation?

1. Acute Severe Portal Hypertension: Pain, ascites, hemorrhagic diarrhea, shock, bowel necrosis.

2. Post-attenuation Seizures (PAS): Refractory seizures occurring within 42 hours post-op (Levetiracetam is often given pre-operatively as prophylaxis).

3. Persistent Hepatic Dysfunction / Persistent Shunting: Liver failure signs or abnormal liver function tests may persist if the hepatic parenchyma fails to regenerate.

What microscopic liver lesions characterize portal vein hypoperfusion on Histopathology?

• Portal Vein Hypoplasia (absence/small interlobular portal veins).

• Arteriolar Proliferation (compensatory hypertrophy of parenchymal hepatic arterioles).

• Lobular Hepatocellular Atrophy.

• Bile duct proliferation and lipid accumulation.

• Note: Presence of severe fibrosis, biliary hyperplasia, and necrosis carries a poor prognosis.

What is Portal Vein Hypoplasia (PVH), and how is it differentiated from CPSS?

• Microscopic vascular malformation (formerly Microvascular Dysplasia) causing small intrahepatic/extrahepatic portal branches and diminished hepatic perfusion without a large macroscopic shunt vessel.

• Breed Predispositions: Maltese, Yorkshire Terrier, Cairn Terrier, Poodle, Papillon.

• Key Differentiator: Protein C activity is typically NORMAL in PVH, whereas it is decreased in CPSS. CTA confirms the absence of a macroscopic shunt vessel.

• Prognosis: Generally good with normal lifespan unless the patient develops severe non-cirrhotic portal hypertension and Acquired Portosystemic Shunts (APSS).

What is a Hepatic Arteriovenous Malformation (HAVM)?

• Direct, high-pressure arterial-to-venous communication proximal to the capillary bed connecting hepatic arteries directly into the portal vein.

• Clinical Presentation: Rapidly causes severe presinusoidal intrahepatic portal hypertension, massive ascites, microhepatica, and splenomegaly.

• Prognosis & Treatment: High morbidity and mortality; requires surgical resection/lobectomy or interventional embolization.