Portosystemic Shunt (Congenital) in Maltese — Management Guide

Comprehensive, practical guide to recognizing, diagnosing and managing congenital portosystemic shunts in Maltese dogs — signs, tests (bile acids, CT angiography), medical care, ameroid constrictor surgery and prognosis.

Quick Overview

• What it is: A congenital portosystemic shunt (PSS) is an abnormal blood vessel that bypasses the liver, allowing portal blood (nutrients and toxins from the gut) to go directly into the systemic circulation without passing through the liver for detoxification and metabolism.
• Who’s at risk: Small breed dogs are overrepresented; Maltese are among the small/toy breeds predisposed to extrahepatic congenital PSS.
• Prognosis: With appropriate care, many dogs do well. Medical management can control clinical signs; surgical attenuation (most commonly with an ameroid constrictor or cellophane band) offers the best chance for long-term resolution. Surgical success for extrahepatic shunts is commonly reported in the range of ~70–90% improvement in clinical signs; perioperative risks include portal hypertension and neurologic complications.

Why this matters for Maltese

Maltese are a small-breed dog species in which congenital extrahepatic portosystemic shunts are reported more often than in large-breed dogs. Early recognition and referral for imaging and possible surgery improves outcomes and reduces long-term liver damage.

Pathophysiology — explained simply

Normally blood from the intestines flows to the liver through the portal vein. The liver removes toxins (especially ammonia), metabolizes nutrients and produces proteins. A congenital PSS is an abnormal vessel or network of vessels that diverts portal blood around — rather than through — the liver. The result is accumulation of neurotoxins (notably ammonia), poor liver development (hypoplasia), and metabolic abnormalities that cause clinical signs collectively called hepatic encephalopathy (HE).

Breed-specific risk factors and prevalence

• Extrahepatic congenital PSS are most common in toy and small-breed dogs: Maltese, Yorkshire Terriers, Miniature Schnauzers, Shih Tzu, and others.
• Exact prevalence is low overall but relatively higher in these breeds; many cases are identified in puppies or young adults.
• Genetic predisposition is likely; breeders should avoid breeding affected animals.

Clinical signs vary with age and severity. Common features:

• Gastrointestinal: intermittent vomiting, diarrhea, poor growth, weight loss, decreased appetite.
• Neurologic (hepatic encephalopathy): subtle disorientation or pacing that waxes and wanes; lethargy; excessive salivation (ptyalism); aimless wandering; head-pressing; ataxia; behavior changes; seizures; coma in severe cases.
• Urinary: ammonium biurate crystals or urolithiasis may occur.
• Other: stunted growth in puppies, poor haircoat.

• Grade 1 (Mild): Subtle behavioral changes, mild lethargy, reduced attention.
• Grade 2 (Moderate): Disorientation, circling, intermittent tremors, ptyalism.
• Grade 3 (Severe): Marked ataxia, stupor, recurrent vomiting, pronounced behavior change.
• Grade 4 (Life-threatening): Seizures, coma, unresponsive.

1) Baseline bloodwork

• CBC: microcytosis is possible.
• Serum chemistry: low blood urea nitrogen (BUN), low cholesterol, hypoalbuminemia (variable), elevated liver enzymes (variable).
• Ammonia: may be elevated during HE but can be variable; sample handling (on ice, rapid processing) is critical.

• Protocol: fasting serum bile acids (fasted sample) and post-prandial bile acids (sample 2 hours after feeding).
• Interpretation: Elevated fasting or post-prandial bile acids suggest hepatic dysfunction or shunting. Bile acids are sensitive but not 100% specific — they are a standard screening test for PSS.
• Practical note: In young dogs with clinical signs, a markedly elevated post-prandial bile acid test supports a diagnosis and should prompt imaging referral.

• Look for ammonium biurate crystals or urate stones (supportive evidence of shunting).

• Abdominal ultrasound: can identify abnormal vessels in experienced hands; often used as first-line imaging but operator dependent.
• CT angiography (CTA): the current gold standard for preoperative anatomic mapping in many centers. CTA provides high-resolution, 3D views of the shunt, its origin and termination, and portal vasculature. It is essential for surgical planning and helps predict whether complete ligation is safe.
• Traditional angiography: used in some centers but CTA has largely replaced it for non-invasive vascular mapping.

• Strongly consider referral to a board-certified veterinary internal medicine specialist and/or a board-certified veterinary surgeon experienced in hepatic surgery for interpretation of imaging and surgical planning.

Goal: reduce clinical signs (especially HE), support liver function, and when feasible, correct the abnormal blood flow surgically.

A) Medical management (initial and long-term for non-surgical candidates)

Medical therapy can control HE and is also used pre-operatively to stabilize patients before surgery.

• Dietary management: highly digestible, moderate-quality protein; avoid abrupt protein restriction that can cause muscle loss. Many clinicians recommend a therapeutic hepatic diet with moderate protein from high-quality sources, divided into small, frequent meals. Exact protein content should be tailored by your veterinarian or veterinary nutritionist.
• Lactulose: osmotic laxative that reduces ammonia absorption by acidifying colonic contents and trapping ammonium. Typical starting dose: lactulose syrup 0.5–1 mL/kg PO every 8–12 hours, titrated to produce 1–2 soft stools per day. (Dose must be individualized.)
• Antibiotics to reduce intestinal ammoniagenic bacteria: commonly metronidazole 10–15 mg/kg PO every 12 hours for short-term control; historically neomycin or ampicillin have been used but have risks and are less favored. Long-term antibiotic use should be guided by your clinician.
• Hepatoprotectants/nutraceuticals: SAMe (S-adenosylmethionine) often 10–20 mg/kg PO once daily (product-dependent), and silybin (milk thistle extract) may be used; ursodeoxycholic acid (ursodiol) 5–10 mg/kg PO every 12–24 hours can be used if cholestasis or biliary sludge is suspected. Evidence is variable; these are adjuncts.
• Supportive care: IV fluids, correction of electrolyte abnormalities, anti-seizure medications if needed (levetiracetam is increasingly used because of favorable safety; dosing commonly 20 mg/kg IV/PO q8–12h as a starting guideline in acute settings — treat under veterinary direction).

B) Surgical options (definitive therapy when feasible)

Surgery aims to attenuate (close gradually) or, rarely, completely ligate the aberrant vessel, allowing portal flow into the liver.

• Gradual attenuation methods (preferred for extrahepatic shunts in small dogs): ameroid constrictor placement or cellophane banding. These devices gradually reduce shunt flow over days to weeks, allowing the portal system to adapt and lowering the risk of postoperative portal hypertension.

• Complete or partial suture ligation: sometimes possible if intraoperative monitoring shows the patient tolerates it; rapid ligation has a higher risk of portal hypertension.

• Reported improvement or resolution of clinical signs after surgical attenuation of extrahepatic shunts is commonly 70–90%, depending on the series and the severity of pre-op hepatic disease.
• Perioperative mortality varies; many recent series report overall mortality in the 5–20% range, with neurologic complications (post-op seizures) among the most serious.
• Post-op monitoring for portal hypertension (vomiting, diarrhea, abdominal pain, ascites), persistent HE, and seizures is critical.

CTA gives a complete vascular map so surgeons know exact shunt anatomy, whether there are multiple shunts, and how portal branches look — this information determines whether gradual attenuation (ameroid/cellophane) is possible and safe.

Long-term management and monitoring

• Rechecks: Bloodwork (CBC, chemistry including bile acids) is commonly rechecked 4–12 weeks after surgery and then periodically (e.g., every 3–6 months initially) to assess liver function and detect persistent shunting or complications.
• Post-op bile acids: normalization or marked improvement in bile acids after attenuation supports successful redirection of portal flow; however, persistently abnormal bile acids do not always correlate with clinical status and require interpretation by your clinician.
• Imaging: If clinical signs persist or bile acids remain abnormal, repeat imaging (CTA or ultrasound) may be needed.
• Lifelong precautions: Even after successful surgery, some dogs have residual hepatic insufficiency and may need long-term dietary management or occasional medical therapy.

• Dogs that undergo successful gradual surgical attenuation (ameroid constrictor or cellophane) commonly experience major improvement in clinical signs and quality of life. Long-term survival is often excellent when surgery is done early before severe hepatic fibrosis develops.
• Medical therapy alone can control signs in many dogs but rarely restores normal hepatic development; long-term medication, dietary management, and monitoring are usually required.
• Factors that worsen prognosis: severe pre-operative HE (especially seizures), advanced hepatic microhepatica (small, poorly functional liver), presence of multiple shunts, and postoperative complications such as seizures or portal hypertension.

• Diet: feed a veterinarian-recommended hepatic diet or a diet formulated for high digestibility and controlled protein. Divide daily food into 2–3 small meals to reduce post-prandial toxin load.
• Medications: give lactulose and antibiotics exactly as prescribed; never stop abruptly without consulting your vet.
• Avoid sedatives and tranquilizers that can worsen HE unless prescribed by your vet.
• Monitoring at home: watch for subtle behavioral changes (confusion, staring, head-pressing), recurring vomiting/diarrhea, or urinary changes; keep a log of episodes and medications.
• Dental and general care: maintain dental health and avoid medications that are hepatotoxic (ask your vet before giving any new medication).
• Breeding: affected dogs should not be bred.

Seek immediate veterinary attention if your Maltese shows any of the following:

• New or worsening neurologic signs: seizures, collapse, coma, persistent unresponsiveness.
• Severe or persistent vomiting and diarrhea with lethargy.
• Signs of abdominal pain, distension (possible portal hypertension/ascites).
• Inability to keep oral medications down or signs of severe dehydration.

• Bile acid testing and interpretation, clinical use: Merck Veterinary Manual — Portosystemic Shunts in Small Animals.
• CTA as gold-standard preoperative imaging and surgical outcomes: multiple peer-reviewed surgical series and veterinary surgical reviews (see representative sources below).
• Medical management recommendations (lactulose, antibiotics, nutritional support) are consistent with consensus clinical practice among veterinary internists and surgical specialists.

• Merck Veterinary Manual — Portosystemic Shunts in Small Animals: https://www.merckvetmanual.com/digestive-system/hepatic-disease-in-small-animals/portosystemic-shunts
• Selected peer-reviewed surgical and internal medicine literature (review articles and case series in Veterinary Surgery and Journal of Veterinary Internal Medicine) and specialty college guidance. For a detailed surgical outcome perspective see multiple published series evaluating ameroid constrictor attenuation of extrahepatic PSS.

• In Maltese puppies and young dogs with poor growth, neurologic episodes, intermittent vomiting or urinary crystals, think of a congenital PSS.
• Bile acids (fasted and post-prandial) are a critical screening test; CTA is usually required for surgical planning.
• Medical therapy (lactulose, antibiotics, dietary management, hepatoprotectants) stabilizes many dogs but does not correct the shunt.
• Surgical gradual attenuation (ameroid constrictor or cellophane band) gives the best chance for long-term resolution; success rates are high when performed and planned appropriately, but perioperative risks exist.

Frequently Asked Questions