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ANATOMY FOR DIAGNOSTIC IMAGING
Great veins (see Figs 4.10 and 1.44) The brachiocephalic veins are formed by the union of the internal jugular and subclavian veins at either side, behind the medial end of the clavicles. On the right, the brachiocephalic vein runs inferiorly behind the right border of the manubrium, anterolateral to the brachiocephalic artery. The left brachiocephalic vein is longer. It descends obliquely behind the manubrium, crossing the origins of the left common carotid and subclavian arteries. It joints with the right brachiocephalic vein to form the superior vena cava behind the junction of the first right costal cartilage with the manubrium. The superior vena cava runs inferiorly behind the right border of the manubrium to enter the right atrium at the level of the third costal cartilage. Its only tributary is the azygos vein, which enters its posterior aspect just above the upper limit of its covering sheath of pericardium. Tributaries of the brachiocephalic veins These are as follows: • Internal thoracic (mammary) veins, which drain into the inferior aspect of the brachiocephalic veins; • Inferior thyroid veins, which arise in the thyroid gland and form a plexus anterior to the trachea. From here, left and right veins drain into the corresponding brachiocephalic vein, close to their confluence; and • Left superior intercostal vein, which drains the left second and third posterior intercostal veins and passes obliquely down anterior to the aortic arch to drain into the left brachiocephalic vein. Radiology of the great vessels The great vessels may be imaged by two-dimensional echocardiography, angiography, CT or MRI. Using MRI one can image in any plane without the need for contrast. A sagittal oblique plane is particularly useful for imaging the thoracic aorta. With two-dimensional echocardiography the aortic root and sinuses, ascending and descending aorta may be visualized using an anterior approach. The arch of the aorta and its branches are occasionally well visualized from a suprasternal approach. THE OESOPHAGUS (Figs 4. 32 and 4. 33 and Figs 4. 45-4. 49) This begins at the level of C5/C6 or the lower border of the cricoid cartilage as the continuation of the oropharynx (see also Chapter 1). Its upper limit is defined by the crico¬ pharyngeus muscle, which encircles it from front to back. It descends behind the trachea and thyroid, lying in front of
the lower cervical vertebrae. It then inclines slightly to the left in the neck and upper mediastinum before returning to the midline at the level of T5, from where it passes to the left again before sweeping forward to pass through the diaphragm. In the chest it passes behind the trachea, left main bronchus, left atrium and upper part of the left ventricle from above downward; it then passes behind the posterior sloping part of the diaphragm before traversing this at the level of T10. The oesophageal hiatus in the diaphragm is surrounded by a sling of fibres from the right cms of the diaphragm. On its left side, where is found the origin of the left subclavian artery, it is grooved by the arch of the aorta. Below this level, its left side lies on left lung and pleural tissue. On its right side it is crossed by the termination of the azygos vein at the level of T4. Below this, the azygos vein lies behind and to its right and it is in contact with right lung and pleura. Posteriorly are the thoracic vertebrae and thoracic duct, the azygos vein and tributaries, and the right posterior intercostal arteries as these cross the vertebral column from the descending aorta. The descending aorta lies to its left side initially. Then, as the oesophagus passes forwards and to the left, it becomes anterior to this vessel in the mid thorax and anterior and to its left as it passes through the diaphragm. In its terminal part in the abdomen it is retroperitoneal and grooves the posterior aspect of the liver. It enters the stomach at the oesophago¬ gastric junction.
