Superior Vena- Cava

SUPERIOR VENA- CAVA 

• SVC collects blood friom the upper half of the body & drains into the right atrium.
• It is formed by the union of two brachiocephalic veins at the level of lower border of 1st right costal cartilage.
• It passes vertically downwards behind the right border of sternum & piercing the pericardium at the level of the second costal cartilage,enters the upper border of the right atrium to end in the upper & posterior part of sinus venorum at the lower border of third right costal cartilage (opposite T5 vertebra).
• Behind the sternal angle (T4 vertebral level), SVC receives the azygous vein.
• SVC is divided into 2 parts-

i.  Upper half (Extrapericardial):

• It lies in the superior mediastinum & azygous vein open into it. 
• It develops from caudal part of right anterior cardinal vein.

ii.  Lower half (Intrapericardinal):

• It lies in midddle mediastinum & is covered by visceral pericardium.
• It develops from right common cardinal vein (Duct of cuvier).

        

DEVELOPMENTAL ANAMOLIES:

1. Left superior vena cava

• This is due to persistence of left anterior cardinal vein & obliteration of anterior cardinal & common cardinal veins on the right side (which normally develop into SVC).
• The left SVC open into right atrium by way of coronary sinus.

2. Double superior vena cava:

• It is due to persistence of left anterior cardinal vein & failure of the left brachiocephalic vein to form.
• The persistant left anterior cardinal vein which is called the left SVC drains into the right atrium by way of coronary sinus.