How is Abernethy syndrome (congenital extra‑hepatic portosystemic shunt) diagnosed and managed in children and young adults?

Abernethy Syndrome: Diagnosis and Management

Overview and Classification

Abernethy syndrome requires classification into Type I (complete shunt with absent intrahepatic portal vein) versus Type II (partial shunt with preserved intrahepatic portal flow), because this distinction determines whether shunt closure or liver transplantation is the appropriate treatment. 1

The malformation diverts splanchnic venous blood directly into systemic circulation, bypassing hepatic metabolism of ammonia and other toxins, which produces the characteristic clinical sequelae. 1

Clinical Presentation

Neurological Manifestations

• Large shunts present with persistent encephalopathic signs from childhood, including mental retardation from hyperammonemia during critical brain development periods. 1
• Small shunts remain silent until the sixth or seventh decade, manifesting as recurrent episodes of encephalopathy in adulthood. 1
• Symptoms include fatigue, cognitive deficits comparable to minimal hepatic encephalopathy, and unexplained hyperammonemia. 1, 2

Hepatic and Systemic Complications

• Portal hypertension develops with splenomegaly, hypersplenism, and variceal hemorrhage. 1
• Hepatopulmonary syndrome occurs with dyspnea on exertion, orthodeoxia, and hypoxia from intrapulmonary vascular dilatations. 3
• Chronic hyperammonemia predisposes to nephrolithiasis. 1
• Benign liver tumors (focal nodular hyperplasia) can transform into hepatocellular carcinoma. 4
• Many cases are identified incidentally during imaging for unrelated reasons. 1, 5

Diagnostic Work-Up

Essential Imaging

• MRI with portal venous phase contrast is the gold standard for diagnosis and classification, accurately delineating vascular anatomy and shunt configuration. 1
• Doppler ultrasonography serves as first-line screening to identify abnormal portosystemic communications. 6

Pre-Operative Assessment

• Conventional angiography with balloon occlusion testing is mandatory before any shunt closure attempt to: (1) evaluate portal vein patency, (2) measure portal pressures before and after temporary occlusion, and (3) determine feasibility of closure. 1
• Never attempt shunt closure without balloon occlusion testing—this prevents catastrophic portal hypertension from inadequate portal vein tolerance. 1

Laboratory and Functional Testing

• Measure serum ammonia levels to quantify the degree of portosystemic shunting. 1, 2
• Neuropsychological testing is required to detect subtle cognitive deficits comparable to minimal hepatic encephalopathy. 1, 2
• Screen for hepatopulmonary syndrome with room air pulse oximetry in upright position. 3
• Contrast-enhanced transthoracic echocardiography or technetium-labeled macro-aggregated albumin lung perfusion scan (shunt fraction >6%) confirms hepatopulmonary syndrome. 3

Management Algorithm

Type II (Partial Shunts)

Shunt closure is the primary therapeutic option and must be pursued before considering transplantation. 1

• Endovascular embolization using occlusion devices (e.g., Amplatzer vascular plugs) placed by interventional radiology is the preferred approach when technically feasible. 3, 1, 7
• Surgical or laparoscopic ligation is an effective alternative. 3, 1
• Pre-operative balloon occlusion testing confirms that the intrahepatic portal system can tolerate closure. 1
• Post-closure, expect portal vein hypertrophy and liver growth from increased trophic flow. 7

Type I (Complete Shunts)

Liver transplantation is the only curative treatment because the intrahepatic portal venous tree is absent, making shunt closure impossible. 1, 8

• Classic orthotopic liver transplantation restores normal portal circulation and resolves complications including hepatopulmonary syndrome and encephalopathy. 8

Indications for Liver Transplantation (All Types)

• Type I malformation with absent portal vein. 1, 2
• Intractable portosystemic encephalopathy refractory to optimal medical therapy. 1, 2
• Failed shunt-closure attempts in Type II malformation. 1
• Hepatopulmonary syndrome in patients not candidates for shunt closure. 3

Medical Management of Complications

Hepatic Encephalopathy

• Lactulose as first-line therapy. 2
• Rifaximin as add-on therapy when lactulose alone is insufficient. 2
• Avoid benzodiazepines and sedatives that worsen encephalopathy. 2
• Rule out precipitating factors including hyponatremia and sepsis. 2

Hepatopulmonary Syndrome

• Supplemental oxygen during periods of increased physical activity provides symptomatic relief. 3
• Shunt closure in Type II malformations reverses hepatopulmonary syndrome by restoring normal portal flow. 3

Portal Hypertension

• Standard medical management for portal hypertension complications. 1
• Octreotide should be started immediately when variceal bleeding is suspected. 1

Surveillance Protocol

• Regular screening with room air pulse oximetry in upright position for all patients with portosystemic shunting to detect hepatopulmonary syndrome. 3
• Serial neuropsychological testing to monitor cognitive function. 1
• Monitor for nephrolithiasis as a complication of chronic hyperammonemia. 1
• Avoid liver biopsy in asymptomatic patients with known vascular malformations. 6

Critical Pitfalls

• Do not perform shunt closure without balloon occlusion testing—this is the most critical error that can result in fatal portal hypertension. 1
• Recognize that hepatopulmonary syndrome can occur without liver dysfunction or cirrhosis in portosystemic shunting. 3
• Investigate congenital portosystemic shunting in any patient with unexplained hyperammonemia, unexplained cognitive impairment, or hepatic encephalopathy without cirrhosis. 1, 2
• Monitor for malignant transformation of benign liver lesions (focal nodular hyperplasia to hepatocellular carcinoma). 4