Page 62 - Clinical Anatomy

ECA1 7/18/06 6:31 PM Page 47

The mediastinum 47

The thoracic duct thus usually drains the whole lymphatic field below
the diaphragm and the left half of the lymphatics above it.
On the right side, the right subclavian, jugular and mediastinal trunks
may open independently into the great veins. Usually the subclavian and
jugular trunks first join into a right lymphatic duct and this may be joined by
the mediastinal trunk so that all three then have a common opening into the
origin of the right brachiocephalic vein.

Clinical features

1◊◊The lymphatics may become blocked by infection and fibrosis due to
the Microfilaria bancrofti. This usually results in lymphoedema of the legs
and scrotum but occasional involvement of the main channels of the trunk
and thorax is followed by chylous ascites, chyluria and chylous pleural
effusion.
2◊◊The thoracic duct may be damaged during block dissection of the neck.
If noticed at operation, the injured duct should be ligated; lymph then finds
its way into the venous system by anastomosing channels. If the accident is
missed, there follows an unpleasant chylous fistula in the neck.
3◊◊Tears of the thoracic duct have also been reported as a complication of
fractures of the thoracic vertebrae to which, in its lower part, the duct is
closely related. Such injuries are followed by a chylothorax.

The thoracic sympathetic trunk (Fig. 38)
The sympathetic chain lies immediately lateral to the mediastinum behind
the parietal pleura.
Descending from the cervical chain, it crosses:
•◊◊the neck of the first rib;
•◊◊the heads of the 2nd to 10th ribs;
•◊◊the bodies of the 11th and 12th thoracic vertebrae.
It then passes behind the medial arcuate ligament of the diaphragm to
continue as the lumbar sympathetic trunk.
The thoracic chain bears a ganglion for each spinal nerve; the first fre-
quently joins the inferior cervical ganglion to form the stellate ganglion. Each
ganglion receives a white ramus communicans containing preganglionic
fibres from its corresponding spinal nerve and donates back a grey ramus,
bearing postganglionic fibres.

Branches
1◊◊Sympathetic fibres are distributed to the skin with each of the thoracic
spinal nerves.
2◊◊Postganglionic fibres from T1–5 are distributed to the thoracic viscera—
the heart and great vessels, the lungs and the oesophagus.
3◊◊Mainly preganglionic fibres from T5–12 form the splanchnic nerves,
which pierce the crura of the diaphragm and pass to the coeliac, superior