What is the management approach for Abernathy syndrome, or congenital absence of the portal vein?

Abernathy Syndrome: Comprehensive Overview

Definition and Pathophysiology

Abernathy syndrome (also called congenital extrahepatic portosystemic shunt) is a rare congenital vascular malformation characterized by agenesis or hypoplasia of the portal vein, causing splanchnic venous blood to bypass the liver and drain directly into the systemic circulation. 1, 2

• Two main types exist: Type I involves complete absence of the portal vein with all splanchnic blood shunting systemically, while Type II involves a hypoplastic but patent portal vein with partial shunting 2
• Type I is further subdivided into Ia (shunt to inferior vena cava) and Ib (shunt to other systemic veins) 3
• Type II includes subtypes based on shunt location and configuration 4, 2

Clinical Manifestations

The syndrome presents with highly variable clinical features, ranging from asymptomatic incidental findings to life-threatening complications 1, 5:

Common Presentations

• Hepatic encephalopathy with hyperammonemia, cognitive deficits, fatigue, and mental retardation (particularly when large shunts are present from childhood) 6, 7
• Hepatopulmonary syndrome (HPS) manifesting as dyspnea on exertion, orthodeoxia, and hypoxia from intrapulmonary vascular dilatations 6, 3
• Portopulmonary hypertension presenting with dyspnea, cough, or syncope 6
• Portal hypertension complications including variceal bleeding, though this is less common in pure portosystemic shunts 4
• Hepatic tumors including hepatocellular carcinoma and adenomas from altered hepatic perfusion 5

Key Diagnostic Clues

• Unexplained hyperammonemia in the absence of cirrhosis should trigger investigation for congenital portosystemic shunting 6, 7
• Symptoms may appear early in life with large shunts or remain dormant until the sixth or seventh decade with smaller shunts 6, 7
• Normal liver enzymes with massive varices and splenomegaly are pathognomonic for extrahepatic portal vein obstruction 8

Diagnostic Approach

MRI with portal venous phase contrast is the gold standard for diagnosis and classification of Abernathy syndrome, as it accurately delineates vascular anatomy and shunt configuration. 6, 7, 8

Essential Diagnostic Studies

• Contrast-enhanced MRI or CT to visualize portal vein anatomy, identify shunt type, and assess hepatic perfusion 6, 7
• Doppler ultrasound as initial screening but insufficient alone for definitive diagnosis 8
• Neuropsychological testing to detect cognitive deficits similar to minimal hepatic encephalopathy 6, 7
• Ammonia levels to assess degree of portosystemic shunting 6, 7

Screening for Complications

• Room air pulse oximetry in upright position to screen for hepatopulmonary syndrome in all patients with portosystemic shunting 6
• Contrast-enhanced transthoracic echocardiography or technetium-labeled macro-aggregated albumin scan (shunt fraction >6%) to confirm HPS 6
• Transthoracic echocardiogram to screen for portopulmonary hypertension (pulmonary artery systolic pressure >40 mmHg) 6
• Cardiac catheterization when echocardiography suggests severe pulmonary hypertension to measure mean pulmonary artery pressure 6

Management Strategy

Primary Treatment Algorithm

The management approach depends critically on shunt type, presence of complications, and feasibility of shunt closure:

For Type II (Partial Shunt with Patent Portal Vein)

Closure of the congenital portosystemic shunt should be considered as the primary alternative to liver transplantation. 6

• Endovascular treatment using occlusion devices placed by interventional radiology is preferred when technically feasible 6
• Surgical ligation of the shunt is an alternative approach 6
• Preoperative evaluation must include portal vein patency assessment, portal pressure measurement before and after test occlusion, and complete angiographic characterization 6
• Shunt closure results in recovery in 46-100% of selected cases with hepatic encephalopathy 7
• MELD score ≥11 predicts higher risk of hepatic encephalopathy recurrence and should guide patient selection for shunt closure versus transplantation 7

For Type I (Complete Absence of Portal Vein)

Liver transplantation is the only curative treatment option when there is absent portal vein or intractable portosystemic encephalopathy. 6, 7

• Auxiliary partial orthotopic liver transplantation (APOLT) is feasible and redirects blood flow to liver segments with normal portal anatomy 3
• Standard orthotopic liver transplantation remains the definitive option 2
• Critical surgical consideration: Absence of portal-systemic pressure differential means no collateral vessels pre-transplant, leading to severe mesenteric edema when the allograft is implanted due to sudden increase in portal pressure 2
• Careful management of mesenteric congestion is crucial to surgical success 2

Management of Specific Complications

Hepatopulmonary Syndrome

• Supplemental oxygen during periods of increased physical activity provides symptomatic relief 6
• Shunt closure should be attempted first in Type II malformations as HPS is generally reversible after restoring normal portal flow 6
• Liver transplantation is indicated when shunt closure is not feasible or in Type I malformations with HPS 6, 3
• HPS resolves within 2 months after successful transplantation 3

Portosystemic Encephalopathy

• Rifaximin as add-on therapy when lactulose alone is insufficient 7
• Avoid benzodiazepines and sedatives that worsen encephalopathy 7
• Rule out precipitating factors including hyponatremia and sepsis 7
• Shunt closure or transplantation for definitive treatment based on anatomy 6, 7

Portal Hypertension and Variceal Bleeding

• Vasoactive drugs (octreotide 50 mcg IV bolus, then 50 mcg/h infusion) should be started immediately when variceal bleeding is suspected 9, 8
• Prophylactic antibiotics (ceftriaxone 1g IV daily for maximum 7 days) reduce mortality and rebleeding 9, 8
• Restrictive transfusion strategy targeting hemoglobin 7-9 g/dL to avoid increasing portal pressure 9, 8
• Endoscopic variceal ligation for esophageal varices 8, 4
• Non-selective beta-blockers for secondary prophylaxis 8, 4
• BRTO or TIPS may be considered based on vascular anatomy and multidisciplinary discussion 9

Portopulmonary Hypertension

• Medical therapy with endothelin receptor antagonists, prostanoids, or sildenafil can stabilize and improve pulmonary pressures 6
• Liver transplantation is indicated for severe PPH after medical optimization, with subsequent resolution of PPH 6

Surveillance and Monitoring

• Regular screening with room air pulse oximetry in upright position for all patients with portosystemic shunting 6
• Serial neuropsychological testing to monitor cognitive function 6, 7
• Periodic imaging to assess for hepatic tumors given increased risk 5
• Monitoring for nephrolithiasis as a complication of chronic hyperammonemia 6

Critical Pitfalls to Avoid

• Do not perform systematic shunt ligation without careful case-by-case evaluation of portal vein patency and pressure gradients 7
• Do not over-transfuse during variceal bleeding as this increases portal pressure and worsens hemorrhage 9, 8
• Do not underestimate mesenteric congestion risk during liver transplantation in Type I malformations due to sudden portal pressure increase 2
• Do not delay transplant evaluation in patients with severe HPS (PaO2 <50 mmHg) as median survival without transplant is less than 12 months in adults 6
• Do not attribute all encephalopathy to portosystemic shunting without excluding other causes including infection, electrolyte abnormalities, and medications 7