The superior vena cava (SVC) is the second largest vein of the body. It collects blood from the upper half of the body — head and neck, upper limbs, thoracic wall, and upper abdomen — and drains it into the right atrium.
Dimensions
- Length: ~7 cm
- Diameter: ~1.25 cm
Formation
Formed at the lower border of the right 1st costal cartilage by the union of the right and left brachiocephalic (innominate) veins.
Course
Passes vertically downwards behind the right border of the sternum.
- Pierces the fibrous pericardium at the level of the right 2nd costal cartilage
- Terminates by opening into the upper part of the right atrium at the lower border of the right 3rd costal cartilage
Subdivisions
| Part | Location |
|---|---|
| Extrapericardial part | Superior mediastinum |
| Intrapericardial part | Middle mediastinum |
Valves
The SVC has no valves — gravity facilitates blood flow downward into the right atrium.
Relations
Anterior
- Right internal thoracic vessels
- Margin of right lung and pleura
- Chest wall
Posterior
- Trachea (posteromedial)
- Right pulmonary artery
- Right principal bronchus
To the Left
- Ascending aorta (anteromedial)
- Brachiocephalic artery
To the Right
- Right phrenic nerve and pericardiophrenic vessels
- Right lung and pleura
Tributaries
- Right and left brachiocephalic veins (form the SVC)
- Azygos vein — arches over the root of the right lung; opens into SVC just before it pierces the fibrous pericardium
- Mediastinal and pericardial veins
Contribution to Cardiac Shadow (X-ray PA view)
The SVC forms the upper part of the right border of the cardiac shadow (mediastinal shadow) in the PA chest radiograph.
Clinical Correlation
Mediastinal syndrome: Signs of SVC obstruction are the first to appear in mediastinal syndrome, making the SVC an important vascular landmark in chest radiological assessment.
No valves: The absence of valves in the SVC means venous pressure waves can be transmitted directly to the neck veins — the basis of JVP assessment in clinical practice.