Anatomy-Posterior Triangle of the Neck

Fascia of neck - Deep cervical fascia #Investing (superficial) layer of deep cervical fascia ~Attachment sites

*superior attachment sites* to external occipital protuberance, superior nuchal line, mastoid process, inferior border of mandible and zygomatic arch - *posteriorly* to nuchal ligament and spinous process of C7 vertebra - *inferiorly* attaches to manubrium, clavicle, and acromion and spine of scapula - fascia splits into anterior and posterior laminae just above manubrium, forming a *suprasternal space* containing fat and the anterior jugular vein - splits to *encircle two main muscles in this layer,* sternocleidomastoid and trapezius - splits to enclose submandibular and parotid salivary glands - a thickening of this fascia forms *stylomandibular ligament* which passes from tip of styloid process to angle of mandible.

Fascia of neck - Deep cervical fascia #Pretracheal layer of deep cervical fascia ~Attachments and continuations

- inferiorly, it passes into the thorax where the anterior layer is *continuous with fibrous pericardium* along the great vessels- pretracheal space occurs between investing and pretracheal layers of fascia which *allows spread of infection to the anterior mediastinum.*

Bones of the neck -Hyoid bone #Location

1) location (Netter 15) - a single, U-shaped bone on midline, superior to larynx, at *level of C3 vertebra.*

Posterior Triangle of the Neck -Nerves #CN XI

1. *CN XI (spinal accessory nerve)* (Netter 128, Moore 9-17, Gray's 8.176) - formed from axons of motor neurons whose cell bodies lie in the accessory nucleus in the upper cervical spinal cord - rootlets from these segments merge as they ascend next to lateral aspect of cord, between dorsal and ventral rami - nerve enters cranial cavity through foramen magnum and leaves through jugular foramen, having temporarily picked up some axons whose neurons where located in nucleus ambiguus of brain stem, but whose fibers leave rest of CN XI just below jugular foramen to run with CN X.

Posterior Triangle of the Neck -Muscles on floor of Posterior Triangle #Splenius Capitis #Levator scapulae

1. and 2. splenius capitis and levator scapulae - review location, attachments, innervation, and actions - they form the two major superior muscles of floor of posterior triangle of neck.

Posterior Triangle of the Neck -Arteriers #Transverse cervical and suprascapular arteries

2) *transverse cervical and suprascapular arteries* - branches from thyrocervical trunk from first part of the subclavian artery - *transverse cervical artery* is the more superior of these two vessels and courses anterior to phrenic nerve, scalene muscles, brachial plexus, and levator scapulae before passing on deep side of trapezius muscle in company with CN XI - *suprascapular artery* crosses anterior scalene muscle, phrenic nerve, third part of subclavian artery, and brachial plexus as it passes deep to clavicle.

Bones of the neck -Hyoid bone #Attachments

2) attachments (Gray's 8.13, 8.158) - This unique bone does not articulate directly with any other bone. Rather, it is connected via muscles and connective tissue structures to the *mandible, styloid process, mastoid process, thyroid cartilage of the larynx, manubrium, and scapula.*

Posterior Triangle of the Neck -Nerves #Brachial plexus

2. *brachial plexus* (Gray's 7.52, 8.175, 7.54 ) - formed by *ventral rami of spinal nerves C5-T1* which exit between anterior and middle scalene muscles in neck - roots of brachial plexus combine into three trunks which cross base of posterior cervical triangle - *supraclavicular branches* of brachial plexus also are present in this part of neck.

Fascia of neck - Deep cervical fascia #Pretracheal layer of deep cervical fascia

2. *pretracheal layer of deep cervical fascia* (Netter 26) - a cylindrical layer of delicate fascia that *encircles the viscera of the neck* (thyroid gland, trachea, and esophagus) - the posterior part is termed the *buccopharyngeal fascia* - superiorly the anterior part attaches to hyoid bone while the buccopharyngeal fascia attaches to the pharyngeal tubercle on the occipital bone of the skull -

Fascia of neck - Carotid sheath #Connections

2. connections - *All three layers of deep cervical fascia blend with the fascia forming the carotid sheath.*

Posterior Triangle of the Neck -Arteriers #Occipital artery

3) *occipital artery* - branch of external carotid artery - present in apex of posterior cervical triangle where it pierces investing layer of deep cervical fascia between SCM and trapezius near superior nuchal line before entering scalp with greater occipital nerve.

Bones of the neck -Hyoid bone #Function

3) function (Gray's 8.251) - serves as an attachment site for muscles involved in tongue movements, swallowing and opening mouth - helps maintain patency of pharynx.

Posterior Triangle of the Neck -Muscles on floor of Posterior Triangle #Posterior Scalene

3. *posterior scalene* - arises from posterior tubercles of transverse processes of C4 - C6 vertebra - inserts on outer surface of rib 2 - acts to elevate rib 2 (during forced inspiration) and flexes neck laterally - innervated by ventral rami of last few cervical spinal nerves.

Fascia of neck - Deep cervical fascia #Prevertebral layer of deep cervical fascia

3. *prevertebral layer of deep cervical fascia* (Netter 26, Gray's 7.47) - a cylindrical sheet of fascia that *encircles the cervical vertebrae and their associated muscles* - fuses superiorly with base of skull - blends inferiorly with endothoracic fascia - prolongation of fascia inferolaterally forms *axillary sheath.*

Posterior Triangle of the Neck -Nerves #Cervical plexus ~formation

3. cervical plexus (Gray's 8.177, Netter 32, 131) a. formation and location - formed from *ventral rami of spinal nerves C1 - C4* - most of these ventral rami divide into anterior and posterior branches which combine to form loops, from which various nerves arise - cervical plexus is located deep to SCM on surface of levator scapulae and middle scalene muscles - *postganglionic sympathetic fibers* are added to these rami via grey rami communicantes from the *superior cervical ganglion.*

Bones of the neck -Hyoid bone #Parts

4) parts (Gray's 8.238) *i) body* - forms bottom part of "U" and faces anteriorly. *ii) greater horns (greater cornua)* - project posteriorly from lateral ends of body. *iii) lesser horns* (lesser cornua) - small conical projections from superior part of hyoid bone at junction between body and greater horns.

Posterior Triangle of the Neck -Muscles on floor of Posterior Triangle #Middle Scalene

4. *middle scalene* - arises from transverse processes of C2 - C7 - inserts on first rib, posterior to groove for subclavian artery - elevates first rib during forced inspirations or flexes neck laterally - innervated segmentally by ventral rami of C3 - C8.

Posterior Triangle of the Neck -Muscles on floor of Posterior Triangle #Anterior scalene

5.* anterior scalene* - arises from transverse processes of C3 - C6 - inserts on first rib on scalene tubercle (between grooves for subclavian artery and vein) - action and innervations same as middle scalene.

Posterior Triangle of the Neck -Boundaries

A. Boundaries (Gray's 8.152, Moore 8.9, Netter 26) - *anterior border* = posterior edge of SCM - *posterior border* = anterior edge of trapezius - *inferior border/base* = middle 1/3 of clavicle - *superior border/apex*= occipital bone on superior nuchal line between attachment sites of SCM and trapezius muscles - *roof* = investing layer of deep cervical fascia - *floor*= splenius capitis, levator scapulae, posterior, middle and anterior scalene muscles, *all covered with prevertebral fascia.*

Bones of the neck -Cervical vertebrae

A. Cervical vertebrae (Moore 4.5) - 7 cervical vertebrae form main bony support for neck - provide for flexibility of neck movements - review their structures.

Sternocleidomastoid muscle -Description

A. Description - The SCM is a strap-like muscle whose oblique course is easily demonstrated in the anterolateral neck - a superficial muscle, encased within the investing layer of cervical fascia.

Overview of the neck -Limits of neck

A. Limits of neck (Gray's 8.4) - superior limit is inferior border of mandible, mastoid process, and superior nuchal line of occipital bone - inferior limit is superior border of manubrium, first rib, and IVD between the C7 and T1 vertebrae.

Fascia of neck -Overview

A. Overview (Gray's 8.151) - The neck contains various compartments - a *visceral compartment* anteriorly, a *vertebral compartment* posteriorly, and *two vascular compartments* laterally. Superficial to these compartments is a layer formed by muscles with their fascial coverings. Each subdivision is surrounded by a layer of fascia allowing freer movement between compartments.

Sternocleidomastoid muscle -Attachment sites

B. Attachment sites - arises by two heads inferiorly - *sternal head* from anterior surface of manubrium - *clavicular head* from superior surface of medial aspect of clavicle - merged heads insert into lateral part of mastoid process and to lateral half of superior nuchal line, near lateral extent of superior attachment site of trapezius. The internal jugular vein lies deeply between the heads inferiorly

Overview of the neck -Contents

B. Contents (Moore 8.1) - parts of digestive and respiratory systems; muscles that move various structures in head, neck, upper limb, and upper thoracic cavity; nerves to head/neck/upper limbs/diaphragm and the main parasympathetic input to the viscera (CNX) and sympathetic input to head and neck (via cervical sympathetic trunk); veins draining head and upper limbs; site for return of most lymph to blood; arteries supplying head and upper limbs, as well as endocrine organs (thyroid and parathyroid glands). These vital structures in the neck are not protected by bones, and thus are vulnerable to trauma.

Posterior Triangle of the Neck -Omohyoid

B. Omohyoid (Grey's 8.168) - inferior belly attaches to superior scapular border, medial to suprascapular notch - superior belly attaches to body of hyoid - tendon between two bellies is anchored to clavicle by fascial sling - functions to depress or fix hyoid - innervated by *ansa cervicalis* (from C1 - C3 ventral rami)

Fascia of neck - Superficial layer of cervical fascia

B. Superficial layer of cervical fascia (Netter 31, Moore 8.5) - is a thin layer of loose connective tissue between the dermis and the deep cervical fascia. It contains cutaneous nerves, superficial veins, and the *platysma (innervated by cervical branch of CN VII).*

Sternocleidomastoid muscle -Actions

C. Actions - unilateral contraction causes lateral flexion of neck, pulling ipsilateral ear towards shoulder and rotating chin upwards and to opposite side - bilateral contraction can cause extension of head via its posterior fibers, flexion of the head by the anterior fibers, or projection of head forward while keeping head level - with head fixed, bilateral contraction lifts up on sternum and clavicle and acts as an accessory respiratory muscle.

Fascia of neck - Deep cervical fascia #Investing (superficial) layer of deep cervical fascia

C. Deep cervical fascia - three encircling layers of dense connective tissue which separate compartments of neck 1. *investing (superficial) layer of deep cervical fascia* (Netter 26, 25, Gray's 8.154, Moore 8.16, 7.69) - is the most superficial layer of deep cervical fascia -

Posterior Triangle of the Neck -Subdivisions

C. Subdivisions of posterior triangle (Gray's 8.172) - inferior belly of omohyoid muscle divides posterior triangle into two triangles of very uneven sizes - superior to omohyoid is *occipital triangle,* named for presence of the occipital artery near its apex - inferior to the omohyoid is the *omoclavicular/subclavian triangle.*

Fascia of neck - Carotid sheath #Definition and contents

D. Carotid sheath (Gray's 8.153) 1. definition and contents - Carotid sheath is a tubular fascial investment for the common and internal carotid arteries, vagus nerve (CN X), internal jugular vein with accompanying deep cervical lymph nodes, carotid sinus nerves, and sympathetic fibers accompanying the carotid arteries.

Sternocleidomastoid muscle -Innervations

D. Innervation - by *spinal accessory nerve (CN XI)* and branches from the ventral rami of spinal nerves C2-C4.

Fascia of neck - Retropharyngeal space

E. *Retropharyngeal space* (Moore 8.4, Netter 26) - is the *largest and most clinically important interfascial space in neck.* It is limited posteriorly by prevertebral fascia, laterally by carotid sheaths, and anteriorly by buccopharyngeal fascia. This space can be divided by a delicate sheet of connective tissue called the *alar fascia* which is a vertical sheet of fascia connected to carotid sheaths laterally. The retropharyngeal space is closed superiorly by the base of cranium but opens inferiorly into the superior mediastinum.

Posterior Triangle of the Neck -Arteriers #THird part of subclavian artery

E. Arteries (Netter 32, Gray's 2.40, 7.38, Netter 34, Moore 8.9) 1) *third part of subclavian artery* - lies lateral to anterior scalene muscle within inferior part of posterior cervical triangle (the omoclavicular triangle) - lies posterosuperior to subclavian vein and crosses anterior surface of first rib - has either no branches or the *dorsal scapular artery* as a branch.

Sternocleidomastoid muscle -Torticollis

E. Torticollis (Moore B8.1) - head drawn down to effected side and face is rotated with chin facing opposite side - can be caused by contraction or shortening of neck muscles - congenital torticollis usually due to damage (during birth) to SCM or incomplete development of this muscle.

Fascia of neck - Retropharyngeal abscess

F. *Retropharyngeal abscess* Retropharyngeal abscesses are caused by bacteria that gain access to this area by lymphatic spread, direct spread from upper respiratory or oral infections, or from pharyngeal trauma, such as from endoscopy. Because this space is open inferiorly, the *infection can spread into the superior and posterior mediastinum.* These abscesses also can influence other surrounding structures, leading to epidural abscesses, jugular vein thrombosis, and carotid artery erosion.

Posterior Triangle of the Neck -Veins

F. Veins (Moore 8.12) - The *external jugular vein (EJV)* is formed near the angle of the mandible by the confluence of the posterior auricular and retromandibular veins. The EJV descends vertically superficial to SCM - lies in medial part of posterior triangle from its mid-point inferiorly - EJV drains into subclavian vein above clavicle and in inferior most part of this triangle. Tributaries to EJV include *transverse cervical, suprascapular, and anterior jugular veins.* A common site for central venous catheterization is into the internal jugular vein as it lies deeply between the two heads of the SCM near the clavicle.

Posterior Triangle of the Neck -Nerves #CN XI ~In the neck

In the neck, CN XI passes through SCM muscle (which it innervates), exits the SCM at the junction of its upper and middle 1/3 to run through the posterior triangle - lying superficial to the prevertebral fascia and running either within or deep to the investing fascia - passes on deep side of trapezius, which it supplies - running with CN XI in neck are proprioceptive sensory fibers and additional motor fibers from C2-C4 spinal cord segments.

Overview of regions of the neck

V. Overview of regions of the neck (Moore 8.6) - *SCM is landmark to divide neck into two main regions* - the *anterior triangle* lies anterior to SCM, inferior to mandible, and lateral to midline - *posterior triangle* lies posterior to SCM, anterior to trapezius, and inferior to superior nuchal line - various other muscles subdivide each of these triangles into smaller triangular regions.

Posterior Triangle of the Neck -Nerves #Cervical plexus ~branches 1)cutaneous nerves

i) *cutaneous nerves* (Moore 8.13, Gray's 8.176) - leave posterior aspect of cervical plexus loops and pierce investing deep cervical fascia at the *"nerve point of the neck"* which is located near middle of posterior edge of the SCM. These cutaneous nerves include: *lesser occipital nerve (C2)* ascends in neck along posterior border of sternocleidomastoid muscle - supplies skin behind and above ear; *great auricular nerve (C2-C3)* curves superficially over lateral border of sternocleidomastoid muscle - ascends towards ear and angle of the mandible - provides cutaneous sensation over area of mastoid process, lower auricle, angle of mandible, and posterior part of parotid gland; *transverse cervical nerve (C2-C3)* which curves anteriorly over SCM, passing deep to external jugular vein and platysma to supply skin of anterior cervical area; and *supraclavicular nerves (C3-C4)* which arise as a single trunk before splitting into three branches to supply skin of upper thoracic wall and shoulder regions.

Posterior Triangle of the Neck -Nerves #Cervical plexus ~branches 2)Ansa cervicalis

ii) *ansa cervicalis* (Moore 8.13, Gray's 8.177, 8.168) - is a nerve loop formed from a *superior root* (from fibers of C1 and C2 nerves that join CN XII for a short course just below its exit from skull) and an *inferior root* (from C2 and C3 ventral rami) - the loop varies in length and exact position, but usually is closely associated with the internal jugular vein and carotid sheath - branches from the ansa cervicalis *innervate omohyoid, sternothyroid, and sternohyoid muscles.*

Posterior Triangle of the Neck -Nerves #Cervical plexus ~branches 3)Phrenic nerve

iii) *phrenic nerve* (Netter 190, Moore 8.13, 8.9) - formed mainly from the ventral ramus of C4 - is sole motor supply for diaphragm (GSE) and is sensory nerve for central diaphragm (GSA) - also contains postganglionic sympathetic fibers (GVE) for blood vessel innervations - in neck, phrenic nerve runs along anterior surface of anterior scalene muscle, posterior to prevertebral fascia and the transverse cervical and suprascapular arteries. An *accessory phrenic nerve* sometimes is present, formed most commonly by a branch from the nerve to the subclavius (C5) - this nerve joins the phrenic nerve either in the root of neck or in the thorax.

Posterior Triangle of the Neck -Nerves #Cervical plexus ~branches 4)Other branches

iv) other branches (Netter 33) - Branches from C2 - C4 *join spinal accessory nerve* at various locations to convey proprioceptive information from SCM and trapezius back to these spinal cord levels, but also likely has some motor fibers. *Direct muscular branches* also leave the cervical plexus to innervate prevertebral muscles of the neck.

Posterior Triangle of the Neck -Nerves #Cervical plexus ~branches 5)Superficial cervical plexus block

v) *superficial cervical plexus block* - can be used for *regional anesthesia* for surgical procedures in neck - involves infiltration of anesthetic in area around middle of posterior border of SCM (the "nerve point of the neck"). Even just anesthetizing in this superficial fashion can be effective for carotid endarterectomy procedures and has the advantages of having the patient awake (for neurologic monitoring) and fewer complications than deep cervical nerve blocks or general anesthesia.