The oesophagus

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 w i th the right brachiocephalic vein to form the superior vena cava behind the junction of the first right costal cartilage w i th 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 w i th 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.

THE THORAX 1 37

Fig. 4.33 Barium-swallow technique showing the oesophagus: (a) upper oesophagus and oropharynx, lateral view; (b) midoesophagus, right anterior oblique view; (c) distal oesophagus; (d) distal oesophagus in another patient with prominent Schatzki ring.

1. Hyoid bone 2. Cricoid cartilage 3. Cricoid impression 4. Cricopharyngeus muscle impression 5. Postcricoid venous plexus 6. Oesophagus

7. Impression caused by osteophytes

(b) 1. Impression of aortic arch 2. Impression of left main bronchus

(c) 1. Cardiac impression (mainly left atrium) 2. A ring: upper limit of ampulla (vestibule) 3. B ring (Schatzki ring): lower limit of ampulla 4. Ampulla (oesophageal vestibule) 5. Diaphragmatic hiatus 6. Oesophageal mucosal folds 7. Oesophagogastric junction (Z-line) 8. Diaphragm

9. Air in fundus of stomach

(d) 1. Schatzki ring 2 . Gastro-oesophageal junction

Blood supply

The blood supply is organized in thirds (with free anastomosis between each third) as follows: • Branches of the inferior thyroid artery supply the upper third; • Branches from the descending aorta supply the middle third; and • Branches from the left gastric artery supply the lower third.

Venous drainage is also found in thirds: to the inferior thyroid veins, the azygos system, and to the portal system via the left gastric vein. Thus there is communication of the systemic and portal venous systems in the oesophagus.

Lymph drainage

This is via a rich paraoesophageal plexus to posterior mediastinal nodes, draining from here to supraclavicular nodes. The lower part drains to left gastric and coeliac nodes.

Radiology of the oesophagus (Fig. 4.33)

Plain films

The right wall of the oesophagus and the azygos vein are outlined by lung, which may be seen on the frontal film as the azygo-oesophageal line. Above the level of the arch of the azygos (at T4 level) the right wall is sometimes seen as the pleuro-oesophageal line. If the oesophagus contains air, the posterior aspect of the anterior oesophageal wall may be seen on the lateral f i l m, behind the trachea. This is known as the 'posterior tracheal stripe'.

Barium studies

The main radiological method of assessing the oesophagus is the barium-swallow technique, where the oesophagus is outlined by barium. Gas is usually swallowed in addition to give a double-contrast examination and to distend the oesophagus. The use of a paralysing agent such as intravenous hyoscine butylbromide (Buscopan) stops intrinsic oesophageal contraction, allowing a better appreciation of oesophageal anatomy.

On the frontal view, the oropharynx may be examined. The piriform fossae are outlined by barium and the epiglottis and base of the tongue show as filling defects in the midline. The cervical oesophagus is seen to curve slightly to the left.

On the lateral view the tongue base and epiglottis are seen from the side, w i th the vallecula between. A posterior indentation caused by the contraction of cricopharyngeus muscle to initiate deglutition indicates the commencement of the oesophagus proper. Just below this, on the anterior wall of the oesophagus, a small impression may be made by a submucosal plexus of veins. The cervical oesophagus is seen to lie on the anterior surface of the vertebral bodies of the cervical spine.

In the chest, the oesophagus is best demonstrated w i th the subject rotated slightly off lateral - usually in the right anterior oblique position. Three major impressions are seen anteriorly. These are made by the aortic arch, the left main bronchus and the left heart chambers (mainly left atrium) from above down. In this position the oesophagus can be seen to curve anteriorly in its distal part to enter the stomach.

On the frontal view, the oesophagus has a left-sided indentation from the aortic arch. The left main bronchus also makes an impression on its left side and may make a linear impression as it indents the anterior wall. The lower oesophagus curves to the left to enter the stomach. In elderly people the course of the oesophagus may be altered by unfolding of the aorta.

The lower end of the oesophagus has a fusiform dilatation just above the oesophagogastric junction. This is called the oesophageal vestibule. On barium examination, the upper part of the vestibule is defined by a transiently contractile ring known as the 'A ring'. The lower limit of the vestibule is defined by another transiently contractile ring known as the 'B ring', 'Schatzki ring' or 'transverse mucosal fold'. The vestibule corresponds to the mano¬ metrically measurable zone of increased pressure that is felt to represent the lower oesophageal sphincter. The upper oesophageal sphincter is formed by cricopharyngeus. In young people the vestibule may span the diaphragm. In this case only the upper ring may be identified radiolog¬ ically. As the oesophagus passes through the diaphragm the latter makes an indentation on it.

The oesophageal mucosa is arranged in longitudinal folds that are best seen when the oesophagus is not distended. These measure approximately 3 mm in w i d t h. The thicker folds of the stomach are seen distally, indicating the oesophagogastric junction. In normal people this may rise into the thorax on swallowing.

Cross-sectional imaging The oesophagus may also be imaged by CT and MRI. On cross-section its relationship to the other structures of the thorax is appreciated (see Figs 4.40 and 4.42-4.44). Its visualization is improved if it contains air. When collapsed it is seen as a narrow, thin-walled structure in the posterior mediastinum. Appreciation of the areas in which aircontaining lung is adjacent to the oesophagus provides an understanding of the mediastinal lines seen on the frontal chest radiograph.