TRIANGLES OF NECK. Part II.

I. TRIANGLES OF NECK ‑ for purposes of description, neck is divided by sternocleidomastoid muscle into an Anterior triangle (anterior to muscle) and a Posterior triangle (posterior to muscle)(Atlas Fig. page 724; Snell Figs. 11-6, 11-7).

A. Posterior triangle (Snell Fig. 11‑8; Atlas Figs. 8.3A -D)

1. Boundaries: Anterior: Sternocleidomastoid; Posterior: Trapezius; Inferior: clavicle; Superficial cover: superficial fascia, platysma and Investing layer; Floor: covered by Prevertebral layer of deep fascia.

2. Contents ‑ Arteries: Subclavian artery, Superficial (Transverse) Cervical and Suprascapular arteries (from Thyrocervical trunk), Occipital artery; Veins: External Jugular vein; Nerves: Roots and Trunks of Brachial plexus, Phrenic nerve, Accessory nerve (CN XI), branches of cervical plexus.

Note: Accessory nerve is considered to divide the posterior triangle into a clinically careful zone (inferior) and carefree zone (superior) (Atlas Fig. 8.3); brachial plexus is in careful zone. (On the other hand, who wants to be operated on by a surgeon who thinks part of your neck is carefree?)

Note: Subclavian vein is not within posterior triangle

B. Anterior triangle of neck (Atlas Figs. page 724, 8.8 - 8.10; Snell Fig. 11-10)

1. Boundaries: anterior by midline of neck, posterior by Sternomastoid muscle, superiorly by lower margin of Mandible; by anatomical convention the anterior triangle is divided into four triangles by anterior and posterior bellies of Digastric and superior belly of Omohyoid which you don't need to know.

2. Contents ‑ Arteries: Carotid sheath with Common Carotid dividing into Internal and External Carotid arteries, numerous branches of External carotid; Veins: Internal Jugular vein; Nerves: Hypoglossal nerve and descending branch of Ansa Cervicalis, Accessory and Vagus nerves; Lymphatics: Deep Cervical chain of lymph nodes.

II. DEEP STRUCTURES OF NECK

A. Thyroid gland (Snell Fig. 11‑14; Atlas Figs. 8.16, 8.17): Composed of two lateral lobes and a central isthmus, which is located below cricoid cartilage; Lateral lobes cover Common Carotid artery; Pyramidal lobe sometimes present above isthmus; when present, it is connected to the hyoid bone via a fibrous strand.

1. Arterial supply: Gland is very vascular.

a. Superior Thyroid artery ‑ accompanied by Superior Laryngeal nerve.

b. Inferior Thyroid artery (branch of Thyrocervical trunk); Inferior Thyroid artery courses near Recurrent Laryngeal nerves (located in groove between trachea and esophagus). (Atlas Figs. 8.20, 8.21)

Note: Care must be taken during thyroid surgery not to damage Laryngeal nerves when ligating vessels.

2. Veins: Superior Thyroid veins follows arteries; Middle Thyroid vein; both veins drain into Internal Jugular vein; Inferior Thyroid vein ‑ Left and right veins join together and enter Left Brachiocephalic vein. (Atlas Figs. 8.16C,E; Snell Fig. 11‑14)

3. Parathyroid glands ‑ 4 very small bodies located posterior to thyroid gland or within gland; position very variable. (Snell Fig. 11‑14)

B. Sympathetic trunk ‑ there are three cervical ganglia (Superior, Middle, Inferior); all 3 ganglia send gray rami to cervical spinal nerves; Superior ganglion sends postganglionic fibers to form a plexus on carotid arteries and their arterial branches to be distributed to most of head; (Snell Fig. 11‑16; Atlas Figs. 8.20, 8.21, 8.24)

C. Thoracic duct at root of neck ‑ follows left margin of esophagus, enters Left Brachiocephalic vein (at junction of Internal Jugular and Subclavian veins) (Snell Fig. 11‑16; Atlas Fig. 8.22)

D. Recurrent laryngeal nerve ‑ Right recurrent laryngeal nerve courses under Subclavian artery; Left recurrent laryngeal under aorta; ascends in groove between trachea and esophagus (Snell Fig. 11‑16; Atlas Fig. 8.20, 8.21)