Page 315 - Clinical Anatomy

ECA5 7/18/06 6:50 PM Page 300

300 The head and neck

The vertebral artery
This is the most important of the branches of the subclavian artery. It
crosses the dome of the pleura, traverses the transverse foramina of the
upper six cervical vertebrae, then turns posteriorly and medially over the
posterior arch of the atlas to enter the cranial cavity at the foramen magnum
by piercing the dura mater. It then runs on the anterolateral aspect of
the medulla to join its fellow in front of the pons to form the basilar artery
(Fig. 212).
The following are the important branches of the vertebral artery:
1◊◊anterior and posterior spinal arteries;
2◊◊posterior inferior cerebellar artery.
From the basilar:
3◊◊anterior inferior cerebellar artery;
4◊◊superior cerebellar artery;
5◊◊posterior cerebral artery (supplying the occipital lobe and medial aspect
of the temporal lobe; Fig. 211).
In addition, in the neck, the vertebral artery gives off spinal branches to
the cervical spinal cord and vertebrae and muscular branches. Within the
foramina transveraria it is accomparied by vertebral veins and a sympa-
thetic plexus which, together with the carotid plexus, provides sympathetic
fibres to the cranial contents.

Clinical features

1◊◊The right subclavian artery is grafted end-to-side into the right pul-
monary artery to short-circuit the pulmonary stenosis of the tetralogy of
Fallot (Blalock’s operation) (see Fig. 33). It is important to note, therefore,
that variations occur in the origins of the right subclavian artery, which may
arise directly from the aortic arch either as its first or as its last branch. In the
latter case, the right subclavian artery passes behind the trachea and
oesophagus in the course to the neck; this vessel may then compress the
oesophagus and produce difficulty in swallowing (dysphagia lusoria). Occa-
sionally, the left subclavian artery has a common origin with the left carotid
from the aortic arch.
2◊◊An aneurysm of the subclavian artery is not rare; it never involves the
thoracic part of the subclavian and its site of election is the third part of the
artery. The close relation of the subclavian artery to the brachial plexus
accounts for the pain, weakness and numbness in the arm which accom-
pany this lesion. Oedema of the arm may result in compression of the sub-
clavian vein.
3◊◊A cervical rib may elevate the subclavian artery and render it unduly
palpable; under these circumstances it may closely simulate an aneurysm
and, in fact, there may be aneurysmal dilation of the artery distal to the
edge of the cervical rib. Vascular changes in the arm associated with a cervi-
cal rib are probably due to peripheral emboli thrown off from thrombi
forming on the walls of the compressed subclavian artery.