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ANATOMY FOR DIAGNOSTIC IMAGING
Fig. 4 . 3 7 Axial CT thorax w i t h contrast to show azygos and hemiazygos system of veins: (a) contrast densely opacifies the arch of the azygos v e i n : (b) accessory hemiazygos vein drains to azygos system (arrows) at T8 level; (c) at a slightly lower level the hemiazygos vein also drains to the azygos v e i n ; (d) below this both the hemiazygos and azygos veins are visible.
IMPORTANT NERVES OF THE MEDIASTINUM The vagus nerves are the tenth cranial nerves and pass through the neck in the carotid sheath. Composed of motor and sensory fibres, the vagus nerve enters the superior mediastinum posterior to the internal jugular vein and brachiocephalic veins. It passes behind the main bronchi, forming a posterior pulmonary plexus; branches then pass to the oesophagus, forming anterior and posterior oesophageal plexuses, which continue into the abdomen through the oesophageal hiatus as anterior and posterior vagal trunks. The recurrent laryngeal nerves arise from the vagi. On the right the recurrent laryngeal nerve winds around the subclavian artery, on the left it winds around the aortic arch.
The phrenic nerves arise from the third to fifth cervical nerves and are the motor supply to the diaphragm. They enter the chest anterior to the subclavian artery and deep to the vein. The right phrenic nerve runs down in front of the superior vena cava, over the right heart border and inferior vena cava to reach the diaphragm. The left phrenic nerve runs down over the aortic arch and left superior intercostal vein, in front of the left hilum, and runs on the left heart border to reach the diaphragm. The sympathetic trunk runs inferiorly in the posterior mediastinum in the paraspinal gutters, coming to lie in front of the bodies of T11 and T12 before passing through the diaphragm behind the medial arcuate ligament to continue as the lumbar sympathetic trunk. It is distributed
