Superior vena cava

At a glance

English

Superior vena cava

Latin (TA2)

Vena cava superior

System

Vein

Region

Trunk

Side

Single, on the midline

About the superior vena cava

This vessel is one of the two great veins that bring systemic blood back to the heart. It collects everything returning from the body above the diaphragm, while the inferior vena cava handles the lower half. It is a broad vessel, roughly two and a half centimetres across, yet only a few centimetres long, and it lies to the right of the ascending aorta in the anterior part of the superior mediastinum.

It begins behind the first right costal cartilage, near its lower edge, where the right and left brachiocephalic veins come together. From there it descends almost straight, behind the first intercostal space. Shortly before it enters the fibrous pericardium, opposite the second right costal cartilage, the azygos vein arches forwards over the root of the right lung and opens into its back. Its lower half therefore lies inside the pericardial sac. It opens into the smooth-walled sinus venarum at the upper, posterior part of the right atrium. There is no valve at this opening, so pressure changes in the right side of the heart pass freely back up into the great veins of the neck.

The wall has the usual three coats: an endothelial intima, a thin media of smooth muscle, and a thick adventitia of collagen and elastic tissue that lets the vessel stretch. Compared with the inferior vena cava, the adventitia holds far less longitudinal smooth muscle. The commonest variant is a left-sided superior vena cava that persists from embryonic life, which usually drains into the coronary sinus; it is seen more often in people with congenital heart disease, and the right vessel may then be normal, small or missing.

Clinically the vein matters in two ways. The tip of a central line, whether placed in the neck or threaded up from the arm, is normally parked in it. It can also be compressed or invaded, most often by lung cancer, secondary deposits or lymphoma, giving superior vena cava obstruction: swollen veins over the face, neck and upper chest, breathlessness, cough and trouble swallowing. Raising both arms may bring on facial flushing (Pemberton's sign). Because no valve guards it, the jugular venous pressure seen in the neck reflects right atrial pressure, and the waves become very prominent in tricuspid regurgitation.

Course and drainage

Begins at

Formed by the right and left brachiocephalic veins joining behind the first right costal cartilage.

Drains into

Opens, without a valve, into the sinus venarum, the smooth upper back part of the right atrium, level with the third right costal cartilage.

Drains

Drains the head, neck, upper limbs and the walls of the thorax (through the azygos vein) into the right atrium.