Page 279 - Clinical Anatomy

ECA5 7/18/06 6:50 PM Page 264

264 The head and neck

to its margins, air is sucked into the vein lumen during inspiration and a
fatal air embolism may ensue.
2◊◊The prevertebral fascia passes across the vertebrae and prevertebral
muscles behind the oesophagus, the pharynx and the great vessels. Above
it is attached to the base of the skull. Laterally, the fascia covers the scalene
muscles together with the phrenic nerve, as this lies on scalenus anterior,
and the emerging brachial plexus and subclavian artery. These structures
carry with them a sheath formed from the prevertebral fascia, which
becomes the axillary sheath.
Inferiorly, the fascia blends with the anterior longitudinal ligament of
the upper thoracic vertebrae in the posterior mediastinum.
Pus from a tuberculous cervical vertebra bulges behind this dense
fascial layer and may form a midline swelling in the posterior wall of the
pharynx. The abscess may then track laterally, deep to the prevertebral
fascia, to a point behind the sternocleidomastoid. Rarely, pus has tracked
down along the axillary sheath into the arm.
3◊◊The pretracheal fascia encloses the ‘visceral compartment of the neck’.
Extending from the hyoid above to the fibrous pericardium below, it
encloses larynx and trachea, pharynx and oesophagus and the thyroid
gland. A separate tube of fascia forms the carotid sheath, containing carotid,
internal jugular and vagus nerve and bearing the cervical sympathetic
chain in its posterior wall. (Some points of clinical significance concerning
this fascia are to be found under ‘The thyroid’, page 267.)

The thyroid gland

The thyroid is made up of (Fig. 189):
1◊◊the isthmus—overlying the 2nd and 3rd rings of the trachea;
2◊◊the lateral lobes — each extending from the side of the thyroid cartilage
downwards to the 6th tracheal ring;
3◊◊an inconstant pyramidal lobe projecting upwards from the isthmus,
usually on the left side, which represents a remnant of the embryological
descent of the thyroid.

Relations (Fig. 188)

The gland is enclosed in the pretracheal fascia, covered by the strap muscles
and overlapped by the sternocleidomastoids. The anterior jugular veins
course over the isthmus. When the thyroid enlarges, the strap muscles
stretch and adhere to the gland so that, at operation, they often appear to be
thin layers of fascia.
On the deep aspect of the thyroid lie the larynx and trachea, with the
pharynx and oesophagus behind and the carotid sheath on either side. Two
nerves lie in close relationship to the gland; in the groove between the
trachea and oesophagus lies the recurrent laryngeal nerve and deep to the