What would a CT (Computed Tomography) angiogram show in a patient with Budd-Chiari syndrome, particularly one with Paroxysmal Nocturnal Hemoglobinuria (PNH) and a history of hepatic vein thrombosis?

CT Angiogram Findings in Budd-Chiari Syndrome

A CT angiogram in Budd-Chiari syndrome will show failure to visualize or non-opacification of the hepatic veins, caudate lobe hypertrophy (in approximately 75% of cases), and a characteristic heterogeneous enhancement pattern with early central enhancement and delayed patchy peripheral enhancement. 1, 2

Primary Vascular Findings

Hepatic Vein Abnormalities

• Non-visualization or non-opacification of hepatic veins is the hallmark finding, though CT has limitations with false positive and indeterminate results in approximately 50% of cases 1
• The hepatic veins may appear as hyperechoic cords replacing normal veins, or show complete absence of normal venous structures 1
• A "spider-web" appearance may be visible near the hepatic vein ostia, representing collateral networks 1

Inferior Vena Cava Changes

• Narrowing of the intrahepatic portion of the IVC occurs due to compression by the hypertrophied caudate lobe 3, 2, 4
• The IVC may show thrombosis or obstruction, particularly in Asian populations where combined IVC/hepatic vein involvement predominates 1

Parenchymal Enhancement Pattern

Characteristic Perfusion Abnormalities

• Early homogeneous central enhancement, particularly at the caudate lobe level, is pathognomonic 1, 2
• Delayed patchy peripheral enhancement with prolonged contrast retention in the liver periphery reflects uneven portal perfusion 1
• This heterogeneous enhancement pattern results from compromised portal venous perfusion and compensatory arterial flow 1

Caudate Lobe Hypertrophy

• Caudate lobe enlargement is found in approximately 75% of patients with Budd-Chiari syndrome 1, 3, 2
• This occurs because the caudate lobe has separate venous drainage directly into the IVC through multiple short hepatic veins, allowing outflow sparing and compensatory hypertrophy when other hepatic veins are obstructed 3, 2

Collateral Vessel Formation

Intrahepatic Collaterals

• Large intrahepatic or subcapsular collateral vessels are present in more than 80% of cases, though CT is less effective than ultrasound in demonstrating these 1
• These collaterals connect hepatic veins to diaphragmatic or intercostal veins with continuous flow 1

Chronic Changes in Longstanding Disease

Nodular Changes

• Macroregenerative nodules that enhance during the arterial phase are common in longstanding Budd-Chiari syndrome 1
• These nodules result from intrahepatic portal vein branch obstruction and increased arterial inflow 1

Special Considerations for PNH-Associated Budd-Chiari

Clinical Context

• In patients with paroxysmal nocturnal hemoglobinuria (PNH), the CT findings remain the same, but the clinical significance differs as these patients require indefinite anticoagulation and may benefit from eculizumab therapy 1
• PNH-associated Budd-Chiari carries high risk of recurrence even after liver transplantation if anticoagulation is discontinued 5
• These patients may develop thrombosis in atypical locations including cerebral and mesenteric veins in addition to hepatic veins 6, 5, 7

Critical Diagnostic Pitfalls

Limitations of CT Angiography

• CT has approximately 50% false positive and indeterminate results when assessing hepatic veins, making it less reliable than Doppler ultrasound for initial diagnosis 1
• Iodinated contrast carries renal toxicity risk and radiation exposure is a concern 1
• CT may miss small hepatic vein thrombosis when large veins appear patent 1

When CT Findings Are Indeterminate

• If CT suggests but does not confirm Budd-Chiari syndrome, Doppler ultrasound by an experienced operator should be used for confirmation and detailed characterization 1
• Direct venography is needed for difficult cases and precise delineation before planning interventional treatment 1