Page 57 - Clinical Anatomy

ECA1 7/18/06 6:31 PM Page 42

42 The Thorax

lower parts of the body; often there are multiple other defects and fre-
quently infants so afflicted die at an early age. More commonly there is a
short segment involved in the region of the ligamentum arteriosum or still
patent ductus. In these cases, circulation to the lower limb is maintained via
collateral arteries around the scapula anastomosing with the intercostal
arteries, and via the link-up between the internal thoracic and inferior epi-
gastric arteries.
Clinically, this circulation may be manifest by enlarged vessels being
palpable around the scapular margins; radiologically, dilatation of the
engorged intercostal arteries results in notching of the inferior borders of
the ribs.
Abnormal development of the primitive aortic arches may result in the
aortic arch being on the right or actually being double. An abnormal right
subclavian artery may arise from the dorsal aorta and pass behind the
oesophagus—a rare cause of difficulty in swallowing (dysphagia lusoria).
Rarely, the division of the truncus into aorta and pulmonary artery is
incomplete, leaving an aorta–pulmonary window, the most unusual congeni-
tal fistula between the two sides of the heart.

The superior mediastinum

This is bounded in front by the manubrium sterni and behind the first four
thoracic vertebrae (Fig. 22). Above, it is in direct continuity with the root of
the neck and below it is continuous with the three compartments of the
inferior mediastinum. Its principal contents are: the great vessels, trachea,
oesophagus, thymus—mainly replaced by fatty tissue in the adult, thoracic
duct, vagi, left recurrent laryngeal nerve and the phrenic nerves (Fig. 17).
The arch of the aorta is directed anteroposteriorly, its three great
branches, the brachiocephalic, left carotid and left subclavian arteries, ascend to
the thoracic inlet, the first two forming a V around the trachea. The brachio-
cephalic veins lie in front of the arteries, the left running almost horizontally
across the superior mediastinum and the right vertically downwards; the
two unite to form the superior vena cava. Posteriorly lies the trachea with the
oesophagus immediately behind it lying against the vertebral column.

The oesophagus

The oesophagus, which is 10in (25cm) long, extends from the level of the
lower border of the cricoid cartilage at the level of the 6 th cervical vertebra
to the cardiac orifice of the stomach (Fig. 35).

Course and relations
Cervical
In the neck it commences in the median plane and deviates slightly to the
left as it approaches the thoracic inlet. The trachea and the thyroid gland are
its immediate anterior relations, the 6 th and 7 th cervical vertebrae and pre-