What are the clinical presentation, diagnostic work‑up, and management options for Abernethy syndrome (congenital extra‑hepatic portosystemic shunt)?

Abernethy Syndrome: Clinical Presentation, Diagnosis, and Management

Classification and Pathophysiology

Abernethy syndrome is classified into Type I (complete shunt with absent intrahepatic portal venous supply requiring liver transplantation) and Type II (partial shunt with preserved intrahepatic portal flow amenable to shunt closure). 1

• The malformation diverts splanchnic venous blood directly into systemic circulation, bypassing hepatic metabolism of ammonia and other toxins 1
• Type I malformations have complete absence of the intrahepatic portal venous tree, making shunt closure impossible 1
• Type II malformations retain some intrahepatic portal flow, allowing for potential shunt closure 1

Clinical Presentation

Neurological Manifestations

• Large shunts cause persistent encephalopathic signs from childhood, whereas small shunts produce recurrent episodes of encephalopathy beginning in adulthood 1
• Symptoms range from subtle cognitive deficits and fatigue to overt encephalopathy with temporal disorientation 1, 2
• Hyperammonemia during critical developmental periods leads to permanent cognitive impairment (mental retardation) 1
• Many cases remain asymptomatic until the sixth or seventh decade of life 1, 2

Hepatic and Systemic Complications

• Portal hypertension develops with splenomegaly, hypersplenism, and variceal hemorrhage 1
• Hepatopulmonary syndrome manifests as exertional dyspnea, orthodeoxia, and hypoxemia from intrapulmonary vascular dilatations 1
• Chronic hyperammonemia predisposes to nephrolithiasis 1
• Type I malformations carry increased risk for hepatocellular carcinoma development, even without cirrhosis 3, 4
• Benign liver lesions (focal nodular hyperplasia, hepatic adenomas) may develop and potentially transform to malignancy 4

Diagnostic Work-Up

Essential Imaging

• Contrast-enhanced MRI or CT with portal venous phase is the gold standard for diagnosis, accurately delineating vascular anatomy and shunt configuration 1, 5
• Imaging must identify: (1) shunt type and location, (2) portal vein patency and caliber, (3) presence/absence of intrahepatic portal radicles, (4) associated liver lesions 5

Pre-Operative Assessment

• Conventional angiography with balloon occlusion testing is mandatory before any shunt closure attempt to measure portal pressures during temporary occlusion and determine feasibility of closure 1
• Failure to perform balloon occlusion testing before closure risks catastrophic portal hypertension 1

Laboratory and Functional Testing

• Measure serum ammonia levels to quantify degree of portosystemic shunting 2
• Neuropsychological testing must be performed to detect subtle cognitive deficits comparable to minimal hepatic encephalopathy 1, 2
• Upright room-air pulse oximetry screens for hepatopulmonary syndrome in all patients with portosystemic shunting 1
• Contrast-enhanced transthoracic echocardiography or technetium-labeled macro-aggregated albumin scan confirms hepatopulmonary syndrome when shunt fraction exceeds 6% 1

Diagnostic Rule

• In any patient with unexplained hyperammonemia, unexplained cognitive impairment, or hepatic encephalopathy without cirrhosis, congenital portosystemic shunting must be investigated 1, 2

Management Algorithm

Type II (Partial) Shunts

Shunt closure via endovascular embolization or surgical/laparoscopic ligation is the primary treatment and should be pursued before considering transplantation. 1

Step 1: Pre-Operative Balloon Occlusion Testing

• Perform angiography with temporary balloon occlusion to confirm portal vein tolerance 1
• Measure portal pressures before and after occlusion 1
• Proceed only if testing demonstrates adequate portal system capacity 1

Step 2: Shunt Closure Method Selection

• Endovascular embolization using occlusion devices (e.g., Amplatzer vascular plugs) is preferred when technically feasible 1, 6
• Surgical or laparoscopic ligation provides effective alternative when endovascular approach is unsuitable 1
• Multiple shunts can be treated simultaneously with multiple occlusion devices 6

Step 3: Post-Closure Outcomes

• Successful closure reverses hepatopulmonary syndrome by restoring normal portal blood flow 1
• Liver volume increases from restored trophic portal flow (documented increase from 843 cm³ to 1191 cm³ in one case) 6
• Recovery from hepatic encephalopathy occurs in 46-100% of selected cases 2

Type I (Complete) Shunts

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

Indications for Liver Transplantation (All Types)

• Presence of Type I malformation with absent portal vein 1, 2
• Intractable portosystemic encephalopathy refractory to optimal medical therapy 1, 2
• Failure of shunt-closure attempts in Type II malformation 1
• Hepatopulmonary syndrome in patients not candidates for shunt closure 1
• Development of hepatocellular carcinoma 3, 4

Medical Management of Complications

Hepatic Encephalopathy

• Rifaximin as add-on therapy when lactulose alone is insufficient 2
• Avoid benzodiazepines and sedatives that worsen encephalopathy 2
• Rule out precipitating factors (hyponatremia, sepsis, gastrointestinal bleeding) 2

Variceal Bleeding

• Initiate octreotide immediately when variceal bleeding is suspected 1
• Standard portal hypertension management applies 1

Hepatopulmonary Syndrome

• Supplemental oxygen during physical activity provides symptomatic relief 1
• Shunt closure is definitive treatment for Type II malformations 1

Surveillance Protocol

Ongoing Monitoring

• Serial neuropsychological testing to monitor cognitive function 1
• Periodic upright pulse-oximetry screening to detect early hepatopulmonary syndrome 1
• Monitor for nephrolithiasis as complication of chronic hyperammonemia 1
• Hepatocellular carcinoma surveillance with semi-annual ultrasound ± AFP in Type I malformations, given increased malignancy risk even without cirrhosis 3, 4

Critical Pitfalls to Avoid

• Never attempt shunt closure without pre-operative balloon occlusion testing—this risks catastrophic portal hypertension 1
• Do not assume absence of symptoms means absence of complications—many patients have subclinical cognitive deficits requiring formal testing 1, 2
• Do not overlook hepatocellular carcinoma risk in Type I malformations, even in young patients without cirrhosis 3, 4
• Recognize that hepatopulmonary syndrome can occur with portosystemic shunting even without underlying liver dysfunction 1
• Do not use MELD score alone for transplant decisions—neurological complications and quality of life are equally important 2