What are the typical presentation, diagnostic work‑up, classification, and management (including indications for liver transplantation versus shunt closure) of congenital extra‑hepatic portosystemic shunt (Abernethy malformation) in children and young adults?

Congenital Extrahepatic Portosystemic Shunt (Abernethy Malformation)

Classification and Pathophysiology

Congenital extrahepatic portosystemic shunts are classified into two distinct types based on portal vein anatomy: Type I (complete shunt with absent intrahepatic portal venous supply) and Type II (partial shunt with preserved intrahepatic portal flow). 1

• Type I involves side-to-end anastomosis with congenital absence of the portal vein, predominantly affects females, and associates with multiple congenital anomalies including polysplenia, cardiac defects, and malrotation 2, 3
• Type II involves side-to-side anastomosis with partially preserved portal venous supply, shows no gender preference, and has fewer associated malformations 2, 3
• The shunt bypasses hepatic metabolism of ammonia and other toxins, leading to hyperammonemia and its sequelae 1

Clinical Presentation

The clinical presentation varies dramatically based on shunt size and type, ranging from incidental discovery to severe neurological and cardiopulmonary complications. 4

Neurological Manifestations

• Hepatic encephalopathy with hyperammonemia, cognitive deficits, fatigue, and mental retardation—particularly with large shunts present from childhood 4
• Symptoms may appear early in life or remain asymptomatic until the sixth or seventh decades 1
• Large shunts cause persistent manifestations starting from childhood, while small shunts lead to recurrent encephalopathy episodes beginning in adulthood 1
• Mental retardation results from hyperammonemia during critical brain development periods 1

Cardiopulmonary Complications

• Hepatopulmonary syndrome manifesting as dyspnea on exertion, orthodeoxia, and hypoxia from intrapulmonary vascular dilatations 4
• High-output heart failure from hyperdynamic circulatory state 5
• Portopulmonary hypertension 6, 7

Hepatic and Other Manifestations

• Portal hypertension with splenomegaly, hypersplenism, and variceal hemorrhage 1, 8, 2
• Regenerative hepatic nodules that can mimic malignancy 2, 3
• Nephrolithiasis from chronic hyperammonemia 1
• Liver dysfunction with elevated transaminases 2
• Many cases are discovered incidentally during imaging for unrelated conditions 1, 8, 6

Diagnostic Work-Up

MRI with portal venous phase contrast is the gold standard for diagnosis and classification, accurately delineating vascular anatomy and shunt configuration. 4

Imaging Algorithm

• Doppler ultrasonography as first-line screening tool to detect abnormal portal flow patterns 4, 8, 3
• Contrast-enhanced MRI or CT to visualize portal vein anatomy, identify shunt type (I vs II), and assess hepatic perfusion 4, 3
• Conventional angiography with balloon occlusion testing is highly recommended preoperatively to assess portal vein patency, measure portal pressures before and after test occlusion, and determine feasibility of shunt closure 1, 8, 3

Laboratory and Functional Assessment

• Ammonia levels to evaluate degree of portosystemic shunting 4
• Neuropsychological testing to detect cognitive deficits similar to minimal hepatic encephalopathy 1, 4
• Complete metabolic panel including liver function tests, coagulation studies, and renal function 9, 2
• Room air pulse oximetry in upright position for screening hepatopulmonary syndrome 4

Key Diagnostic Recommendation

• Investigate congenital portosystemic shunting in any patient with unexplained hyperammonemia, mental retardation, or clinical picture compatible with hepatic encephalopathy in the absence of cirrhosis 1, 9

Management Strategy

Management depends critically on shunt type, presence of complications, and technical feasibility of shunt closure—with Type I requiring liver transplantation and Type II amenable to shunt closure. 4

Type II Malformations (Partial Shunt)

• Shunt closure is the primary alternative to liver transplantation and should be considered first 4
• Endovascular occlusion using devices placed by interventional radiology is preferred when technically feasible 4
• Surgical or laparoscopic ligation is an alternative approach 1
• Success rates for radiological embolization or surgical ligation range from 46-100% in selected patients 9
• Preoperative balloon occlusion testing is crucial to confirm portal vein tolerance and predict outcomes 1, 8

Type I Malformations (Complete Shunt/Absent Portal Vein)

• Liver transplantation is the only curative treatment and definitive option 1, 4, 3
• Shunt closure is not feasible due to absent intrahepatic portal venous supply 3

Indications for Liver Transplantation

• Type I malformation (absent portal vein) 1, 4, 3
• Intractable portosystemic encephalopathy refractory to medical therapy 1, 4, 9
• Failed shunt closure attempts in Type II 1
• Disabling symptoms unresponsive to drug and non-drug treatments 9

Management of Specific Complications

Hepatopulmonary Syndrome

• Supplemental oxygen during physical activity for symptomatic relief 4
• Shunt closure should be attempted first in Type II malformations as hepatopulmonary syndrome is generally reversible after restoring normal portal flow 4
• Liver transplantation indicated when shunt closure is not feasible or in Type I malformations 4

Portosystemic Encephalopathy

• Lactulose as first-line medical therapy 9
• Rifaximin as add-on therapy when lactulose alone is insufficient 4, 9
• Avoid benzodiazepines and sedatives that worsen symptoms 9
• Rule out precipitating factors including hyponatremia and sepsis 9

Portal Hypertension and Variceal Bleeding

• Standard medical management for heart failure and portal hypertension 1
• Vasoactive drugs such as octreotide should be started immediately when variceal bleeding is suspected 4

Surveillance and Monitoring

All patients with portosystemic shunting require lifelong surveillance even if asymptomatic at diagnosis. 4

• Regular screening with room air pulse oximetry in upright position for hepatopulmonary syndrome 4
• Serial neuropsychological testing to monitor cognitive function 4
• Monitoring for nephrolithiasis as complication of chronic hyperammonemia 4
• Periodic imaging to assess for development of hepatic nodules 2, 3

Critical Pitfalls to Avoid

• Do not perform liver biopsy in suspected cases—diagnosis depends on imaging and portal venography 6
• Do not delay diagnosis in pediatric patients with unexplained portal hypertension or splenomegaly 8
• Do not attempt shunt closure without preoperative balloon occlusion testing to confirm portal vein tolerance 1, 8
• Do not misdiagnose regenerative hepatic nodules as malignancy—these are common in Abernethy malformation 2, 3
• Do not overlook associated congenital anomalies, particularly cardiac defects and polysplenia in Type I 2, 3