Abnormal Systemic Venous Drainage

Classification:

• Union of superior vena cava (SVC) or inferior vena cava (IVC) with the left atrium (LA).
• Persistent left SVC.
• Absent hepatic segment of IVC.

Union of SVC or IVC with LA

It is a very rare anomaly.
All cases are cyanotic.
If both SVC & IVC join LA, the right heart is hypoplastic.
Once diagnosed, surgery is indicated: An intra-atrial baffle is placed to direct the caval blood to RA.

Persistent left superior vena cava

Significance:

This anomaly is hemodynamically insignificant.
It may, however, cause difficulties during cardiac catheterization from the left arm.
It may also cause a bloody field during open heart surgery and complicate matters.

Pathology:

A persistent left SVC usually joins left innominate vein or coronary sinus.
Rarely it joins LA, in association with: asplenia, or polysplenia, or an atrial septal defect (ASD).

Mirror-image venous system:

Rarely the venous system in the neck is a mirror image of normal:
The right innominate vein crosses to the left side, joins the left vein & forms a left SVC that drains into the coronary sinus.

Absent hepatic segment of IVC

Definition and pathology:

In absent hepatic segment of IVC (also called: Continuity of IVC with the Azygos or hemi-Azygos veins, or Candy-Cane deformity), the hepatic segment of IVC is absent, the rest of IVC joins either the Azygos or the hemi-Azygos vein which then joins SVC.
The hepatic veins join together and form a trunk that joins RA in place of IVC.

Anatomy and tributaries of the inferior vena cava.

http://www.instantanatomy.net/diagrams/AB016.jpg

Inferior vena cava and Azygos and Hemi-Azygos veins.

http://veinforum.org/images/hbk/11a.jpg

Embryology:

• The hepatic (pre-renal or upper) segment of IVC is formed by the right vitelline vein.
• The renal (middle) segment of IVC is formed by the right sub-cardinal vein.
• The post-renal (lower) segment of IVC is formed by the right supra-cardinal (sacro-cardinal) vein.

Segments of the inferior vena cava.

http://download.imaging.consult.com/ic/images/S1933033207763310/gr8-midi.jpg

Chest x-ray:

• With drainage to Azygos vein: Fullness of right side of superior mediastinum.
• With drainage to hemi-Azygos vein: Fullness of left side of superior mediastinum.

Diagnosis and significance:

Leg venography is diagnostic.
The anomaly has no clinical significance but may cause difficulties during cardiac catheterization.