What is the difference between interrupted Inferior Vena Cava (IVC) with azygous continuation and hemiazygous continuation?

Difference Between Interrupted IVC with Azygous and Hemiazygous Continuation

Interrupted inferior vena cava (IVC) with azygous continuation differs from hemiazygous continuation primarily in the anatomical pathway through which venous blood returns to the heart - azygous continuation routes blood through the right-sided azygous vein system, while hemiazygous continuation routes blood through the left-sided hemiazygous venous system.

Anatomical Differences

Azygous Continuation

• Blood from the lower body flows into the azygous vein system on the right side of the vertebral column
• The azygous vein ascends along the right side of the thoracic spine
• It eventually arches forward over the right main bronchus to join the superior vena cava (SVC)
• This creates a characteristic "hook" appearance on imaging at the azygous arch
• The dilated azygous vein may be mistaken for a right paratracheal mass 1

Hemiazygous Continuation

• Blood from the lower body flows into the hemiazygous system on the left side of the vertebral column
• The hemiazygous vein ascends along the left side of the thoracic spine
• It typically crosses midline at the level of T8-T9 to join the azygous vein
• The hemiazygous vein may also connect with the left brachiocephalic vein
• This creates a more complex venous drainage pattern with left-to-right crossover

Clinical Implications

Both variants represent developmental anomalies where the infrahepatic portion of the IVC fails to form properly. In both cases:

• The hepatic segment of the IVC is typically absent
• Hepatic veins drain directly into the right atrium
• The condition is usually asymptomatic and discovered incidentally 2, 3
• Both variants occur in approximately 1 in 5000 people 4

However, important clinical considerations include:

1. Procedural challenges: Transfemoral access to the right heart can be difficult with either variant, requiring alternative approaches for procedures like temporary pacing 5

2. Imaging misinterpretation: Both variants can be misdiagnosed as pathology:

   • Azygous continuation may mimic right paratracheal masses
   • Hemiazygous continuation may be confused with left-sided mediastinal adenopathy
   • Both can be mistaken for aortic pathology on transesophageal echocardiography 1

3. Thrombosis risk: Both variants are associated with increased risk of deep vein thrombosis and pulmonary embolism due to altered venous flow dynamics 2

4. Surgical considerations: Special attention is required during right thoracotomy procedures due to the enlarged azygous or hemiazygous vessels 4

Diagnostic Features

The diagnosis is typically made through cross-sectional imaging:

• CT or MRI showing absence of the intrahepatic IVC
• Dilated azygous or hemiazygous veins
• Direct drainage of hepatic veins into the right atrium
• Venacavography can confirm the diagnosis 3

Clinical Management

No specific treatment is required for the anatomical variant itself, but awareness is crucial for:

• Planning vascular interventions
• Interpreting imaging studies correctly
• Surgical planning, especially for right thoracotomy 4
• Considering alternative access routes for procedures requiring IVC access 5

These anatomical variants should be recognized by clinicians to avoid misdiagnosis and to appropriately plan interventional procedures that might otherwise be complicated by the unusual venous anatomy.