23 : The Anterior Triangle and Root of Neck

Thyroid Gland

Position:

• Antero- inferior part of the neck

• Isthmus is midline between second and fourth tracheal rings

• The lobes are antero-lateral between C4 and C6

• Lobes are between trachea and esophagus medially and carotid sheath laterally.

• Deep to platysma and strap muscles.

Relations:

Isthmus

Anteriorly:	Strap muscles, anterior jugular veins
Posterior	Second to fourth tracheal rings
Laterally	Continous with lobes
Superiorly	Anastomosis of superior thyroid artery
Inferiorly	Anastomosis of inferior thyroid artery

Lobes

Antero laterally	Strap muscles, anterior jugular veins
Posterior	Parathyroid glands, prevertebral muscles.
Postero-laterally	Carotid sheath and its contents (common carotid artery (4),internal jugular vein (5) ,vagus nerve (6). The sympathetic chain is nearby.
Medially	Larynx(1) pharynx and external laryngeal nerve above, trachea,oesophagus(2) and recurrent laryngeal nerve below.

Blood supply:

Arterial

• Inferior thyroid artery from the thyrocervical trunk

• Superior thyroid artery from the external carotid artery.

• Occasional (unpaired) thyroidea ima (middle thyroid) from brachiocephalic trunk .

• Several unnamed twigs from pharyngeal and tracheal vessels.

All these arteries anastomose with each other.

Venous

• Superior thyroid vein (A) – Internal jugular vein

• Middle thyroid vein (B) – Internal jugular vein

• Inferior thyroid vein (C) – Brachio cephalic vein.

The inferior thyroid veins cover the trachea inferior to the thymus. They constitute potential sources of haemorrhage in tracheostomy.

Lymphatic drainage:

• Inferior deep cervical lymph nodes [1].

• Prelaryngeal lymph nodes [2]

• Paratracheal lymph nodes [3].

• Pretracheal lymph nodes. [4]

• Parasternal lymph nodes.

Some may empty directly into the thoracic duct.

Innervation:

Autonomic innervation from the cervical sympathetic ganglia and vagus. This innervation is vasomotor and affects the gland indirectly through the action on blood vessels.