MEDIASTINUM(^4) Neruses: (i) Phrenic, (ii) deep cardiac plexus.
5 Lymph nodes: Tracheobronchial nodes.
6 Tubes: (i) Bifurcation of trachea, (ii) the right and left
principal bronchi.
Poslefior Mediostinum
ff*um s
Anteriorly: (i) Pericardium, (ii) bifurcation of trachea,
(iii) pulmonary vessels, and (iv) posterior part of the
upper surface of the diaphragm.
Posteriorlq; Lower eight thoracic vertebrae and
intervening discs.
On each side:Mediastinal pleura.
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7 Oesophagus (Fig. 77.4).
2 Arteries: Descending thoracic aorta and its branches.
3 Veins: (i) Azygos vein, (ii) hemiazygos vein,
and (iii) accessory hemiazygos vein.
4 Nentes: (i) Vagi, (ii) splanchnic nerves, greater, lesser
and least, arising from the lower eight thoracic
ganglia of the sympathetic chain (see Fig. 15.1).
5 Lymph nocles and lym:phatics:
a. Posterior mediastinal lymph nodes lying along-
side the aorta.
b. The thoracic duct (Fig. 17.4).
Thoracrc ducl
Oesophagus
Trachea
Arch of aoda
Descending thoracic aorta
Thoracic duct
Oesophagus
Azygos vein
Fig. 17.4: Structures in the posterior part of the superior media-
stinum, and their continuation into the posterior mediastinum.
Note the relationship of the arch of the aorta to the left bronchus,
and that of the azygos vein to the right bronchus
The prevertebral layer of the deep cervical fascia
extends to the superior mediastinum, and is
attached to the fourth thoracic vertebra. An
infection present in the neckbehind this fascia can
pass down into the superior mediastinum but not
lower down.
The pretracheal fascia of the neck also extends to
the superior mediastinum, where it blends with
the arch of the aorta. Neck infections between the
pretracheal and prevertebral fasciae can spread
into the superior mediastinum, and through it into
the posterior mediastinum. Thus mediastinitis can
result from infections in the neck (see Chapter (^3) of
Volume 3).
There is very little loose connective tissue between
the mobile organs of the mediastinum. Therefore,
the space can be rgadily dilated by inflammatory
fluids, neoplasms, etc.
In the superior mediastinum, all large veins
are on the right side and the arteries on the left
side. During increased blood flow veins expand
enormously, while the large arteries do not expand
at all. Thus there is much 'dead space' on the
right side and it is into this space that tumour
or fluids of the mediastinum tend to project
(Fig. 17.5).
Compression of mediastinal structures by any
tnmour gives rise to a group of symptoms knerwn
as medinstinal syndrome. The common symptoms
are as follows.
a Obstruction of superior vena cava gives rise to
engorgement of veins in the upper half of the
body.
b. Pressure over the trachea causes dyspnoea, and
cough.
c. Pressure on oesophagus calrses dysphagia.
d. Pressure or the left recurrent laryngeal nerve
6;ives rise to hoarseness of voice (dysphonia).
e. Pressure on the phrenic nerve causes paralysis
of the diaphragm on that side.
f. Pressure on the intercostal nerves gives rise to
pain in the area supplied by them. It is called
i ntercostal neuralgia.
g. Pressure on the vertebral column may cause
erosion of the vertebral bodies.
The common causes of mediastinal syndrome are
bronchogenic carcinoma, Hodgkin's disease causing
enlarg5ement of the mediastinal lymph nodes,
aneurysm or dilatation of the aorta, etc.
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