Wednesday, November 17, 2010

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.

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