Superior vena cava
Vena cava superior
Also known as: SVC
The superior vena cava is a large, valveless vein about 7 cm long. It returns blood from the head, neck, upper limbs and chest wall to the right atrium.
Overview
The SVC is formed behind the lower border of the right 1st costal cartilage, where the right and left brachiocephalic veins join. It runs straight down along the right side of the ascending aorta. Just before it enters the pericardium, at the level of the 2nd costal cartilage, it receives the azygos vein, which arches over the root of the right lung at T4. The SVC opens into the upper part of the right atrium at the level of the 3rd right costal cartilage. Its lower half lies inside the pericardium.
The SVC has no valves, so pressure in it reflects right atrial pressure. This is why the jugular venous pressure can be used to estimate central venous pressure.
- Location
Superior and middle mediastinum, to the right of the ascending aorta.
Anatomy
- Tributaries
The right and left brachiocephalic veins, the azygos vein and small pericardial and mediastinal veins.
- Relations
To the right: the right lung and pleura and the right phrenic nerve. To the left: the ascending aorta. Behind it: the trachea, the right vagus nerve, the right pulmonary artery and the right main bronchus.
Function
- Returns venous blood from the upper body to the right atrium (about one-third of total venous return at rest).
Clinical significance
SVC obstruction
Most SVC obstruction is caused by cancer, especially small-cell lung cancer and lymphoma. Thrombosis around central lines or pacing wires is another cause. Patients have a swollen, flushed face and arms, distended neck and chest-wall veins that do not pulsate, and breathlessness. Pemberton's sign (facial plethora when both arms are raised) may be positive. Blood finds collateral routes through the azygos, internal thoracic and epigastric veins.
Central venous catheter position
The tip of a central line should lie in the lower SVC or at the junction with the right atrium. On a chest radiograph this is roughly at the level of the carina.
Persistent left SVC
A persistent left SVC, the commonest thoracic venous anomaly, drains into the coronary sinus. It can complicate placement of pacemaker and central venous lines.
Compiled from standard anatomy and physiology references — see the Cardiovascular System sources. For education only; not medical advice.