The superior mediastinum

Abstract 

The mediastinum is the area of the thorax that lies between the two pleural sacs. It is further divided by an imaginary line passing from the manubriosternal junction (angle of Louis) in front and the T4/T5 vertebral junction behind into a superior and inferior compartment. The inferior mediastinum contains the heart, within its pericardial sac, together with the descending aorta and lower oesophagus. The contents of the superior mediastinum comprise the retrosternal structures, the remnant of thymus and the great veins. These are made up as follows: the right and left brachiocephalic veins form from the internal jugular/subclavian junction behind each sternoclavicular joint. The right passes directly downwards; the left passes obliquely to join the right at the level of the first right costomanubrial junction to form the superior vena cava. This is joined by the vena azygos and drains into the right atrium. Posteriorly, the superior mediastinum contains the trachea (the right vagus descends on its right border). The trachea itself lies immediately in front of the oesophagus, which lies on the bodies of T1–T4. The left recurrent laryngeal nerve lies in the tracheo-oesophageal groove on its left side, while the thoracic duct lies on the left of the oesophagus. The aortic arch commences from the ascending aorta and arches posterolaterally to the left over the pulmonary trunk and left pulmonary artery. It is crossed by the left phrenic nerve and the left vagus nerve. The latter gives off the left recurrent laryngeal nerve. The aortic arch gives off from its upper margin the brachiocephalic, left common carotid and left subclavian arteries. These do not give off branches until they have left the thorax.

Keywords: aortic arch, brachiocephalic artery, left and right brachiocephalic veins, left common carotid artery, left subclavian artery