Deep Neck and Prevertebral Region Structures

Trachea

• Begins at the inferior border of the cricoid cartilage (C6).
• Has 16 to 20 incomplete hyaline cartilaginous rings that open posteriorly to prevent the trachea from collapsing.

Esophagus

• Begins at the lower border of the pharynx at the level of the cricoid cartilage (C6) and descends between the trachea and the vertebral column.
• The cricopharyngeus muscle, the sphincter of the upper esophageal opening, remains closed except during deglutition (swallowing) and emesis (vomiting).
• Is innervated by the recurrent laryngeal nerves and the sympathetic trunks and receives blood from branches of the inferior thyroid arteries.

Thyroid gland

• Is an endocrine gland that produces thyroxine and thyrocalcitonin , which are essential for metabolism and growth. The thyroid takes iodine from food to produce thyroid hormones.
• Consists of right and left lobes connected by the isthmus , which usually crosses the second and third (or second, third, and fourth) tracheal rings. An inconstant pyramidal lobe extends upward from the isthmus, usually to the left of the midline, and may be anchored to the hyoid bone by a fibrous or muscular band known as the levator glandulae thyroideae.
• Is supplied by the superior and inferior thyroid arteries and sometimes the thyroid ima artery , an inconsistent branch from the brachiocephalic trunk.
• Drains via the superior and middle thyroid veins to the internal jugular vein and via the inferior thyroid vein to the brachiocephalic vein.

Parathyroid glands

• Are endocrine glands that play a vital role in the regulation of calcium and phosphorus metabolism.
• Secrete parathyroid hormone, which is essential to life because low calcium levels lead to lethal neuromuscular disorders.
• Usually consist of four (two to six) small ovoid bodies that lie against the dorsum of the thyroid under its sheath but with their own capsule.
• Are supplied chiefly by the inferior thyroid artery.

Thyroid cartilage

• Is a hyaline cartilage that forms a laryngeal prominence known as the Adam's apple , which is particularly apparent in males.
• Has a superior horn that is joined to the tip of the greater horn of the hyoid bone by the lateral thyroid ligament and an inferior horn that articulates with the cricoid cartilage.

Vagus nerve

• Runs through the jugular foramen and gives rise to the superior laryngeal nerve, which is divided into the external and internal laryngeal nerves.

1) External laryngeal nerve

• Runs along with the superior thyroid artery.
• Supplies the cricothyroid and inferior pharyngeal constrictor muscles.

2) Internal laryngeal nerve

• Accompanies the superior laryngeal artery.
• Supplies the sensory fibers to the larynx above the vocal cord and taste fibers to the epiglottis.

Sympathetic trunk

• Is covered by the prevertebral fascia (the prevertebral fascia splits to enclose the sympathetic trunk).
• Runs behind the carotid sheath and in front of the longus colli and longus capitis muscles.
• Contains preganglionic and postganglionic sympathetic fibers, cell bodies of the postganglionic sympathetic fibers, and visceral afferent fibers with cell bodies in the upper thoracic dorsal root ganglia.
• Receives gray rami communicantes but no white rami communicantes in the cervical region.
• Bears the following cervical ganglia:

1) Superior cervical ganglion

• Lies in front of the transverse processes of vertebrae C1 to C2, posterior to the internal carotid artery and anterior to the longus capitis.
• Contains cell bodies of postganglionic sympathetic fibers that pass to the visceral structures of the head and neck.
• Gives rise to the internal carotid nerve to form the internal carotid plexus; the external carotid nerve to form the external carotid plexus; the pharyngeal branches that join the pharyngeal branches of the glossopharyngeal and vagus nerves to form the pharyngeal plexus; and the superior cervical cardiac nerve to the heart.

2) Middle cervical ganglion

• Lies at the level of the cricoid cartilage (vertebra C6).
• Gives rise to a middle cervical cardiac nerve , which is the largest of the three cervical sympathetic cardiac nerves.

3) Inferior cervical ganglion

• Fuses with the first thoracic ganglion to become the cervicothoracic (stellate) ganglion.
• Lies in front of the neck of the first rib and the transverse process of vertebra C7 and behind the dome of the pleura and the vertebral artery.
• Gives rise to the inferior cervical cardiac nerve.

4) Ansa subclavia

• Is the cord connecting the middle and inferior cervical sympathetic ganglia, forming a loop around the first part of the subclavian artery.

Thoracic duct

• Ascends through the posterior mediastinum between the aorta and azygos vein.
• Arches laterally over the apex of the left pleura, posterior to the left carotid sheath, and anterior to the sympathetic trunk and vertebral and subclavian arteries; runs behind the left internal jugular vein; and then usually empties into the left brachiocephalic vein at the junction of the left internal jugular and subclavian veins.