unit 17 - anterior triangle of the neck

8/6/2019 Unit 17 - Anterior Triangle of the Neck

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The Anterior and Posterior

Triangles of the Neck


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Anterior Triangle of the Neck


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BONY SKELETON OF THE NECK

Like other regions of thebody, the neck has a centralbony skeletal core uponwhich other structures attachor are related. The bones ofthe neck consist of the base

of the skull and the 7 cervicalvertebrae.

If we take a look at the baseof the skull, the major partsthat are related to the upper

neck are the: Foramen magnum Occipital condyle (articulates

with the superior process of theatlas.

External occipital protuberance

Mastoid process


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Below the base of the

skull, you will find the

vertebral column. The top

vertebrae (7 cervical)provide support for the

neck structures. You will

also note that these

vertebrae allow passage

of an important arterialsupply to the brain and

brain stem, the vertebral

artery.


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The first cervical vertebra is theatlas and is considered an atypicalcervical vertebra because it has nobody or spinous process. Itarticulates with the occipital

condyles of the skull above it andwith the superior articularprocesses of the axis below it. Italso articulates with the dens of theaxis below. If viewed from above,you can identify the following partsof the atlas:

Anterior arch Anterior tubercle

Superior articular process(articulate with the occipital condyleof the skull)

Foramen transversarium

Transverse process

Posterior arch

Posterior tubercle

Vertebral canal (continuous with theforamen magnum at the base of theskull). The brain stem continuesinferiorly as the spinal cord at the

margin of the foramen magnum.


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The axis is the secondcervical vertebra. Thisvertebral is also called an

atypical vertebra because ithas an upward projectioncalled the dens thatarticulates with the inneraspect of the anterior arch of

the atlas just posterior to theanterior tubercle. Some ofthe identifiable parts are the: dens

body

superior articular process transverse process with its

vertebral foramen

pedicle

lamina

bifid spine


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The 3rd, 4th, 5th, and 6thcervical vertebrae are known asthe typical cervical vertebraebecause they all have the samecharacteristics and except forthe foramen for the vertebralartery similar to other typicalvertebrae of the spinal cord.These characteristics are:

body

pedicle

foramen for vertebral artery

superior articular process

lamina

spinous process (bifid in case of

cervical vertebrae) vertebral canal

transverse process (consists ofa groove that carries a cervicalspinal nerve and, of course theforamen for the vertebral artery)


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The 7th cervical vertebra starts to pick up

characteristics of the upper thoracic vertebrae. Differences from other cervical vertebrae no foramen for the vertebral artery

After the vertebral artery arises from the subclavian artery, itenters the transverse foramen of the 6th cervical vertebrabypassing the 7th

may not have a bifid spinous process

the spinous process of the 7 cervical vertebra islonger than the other cervical vertebrae

it is not buried under the ligamentum nuchae of theneck so it is easy to see and to palpate and is calledthe vertebra prominens

can serve as a surface landmark demarcating the neck(cervical) from the thoracic regions of the body.


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AnteriorNeck

Common carotid artery (cc)

Internal carotid artery (ic)

External carotid artery (ec)

Carotid sinus

MajorLandmarks


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Superficial structures

from the lateral view ofthe neck. sternomastoid

trapezius

occipital lymph nodes (on)

retroauricular lymph nodes(ran)

superficial cervical lymphnodes (scn)

submental lymph nodes(smn)

buccal lymph nodes (bn) parotid lymph nodes (pn)

submandibular lymphnodes (not labeled but unerangle of mandible)


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Abnormalities of the superficial neck Swollen lymph nodes sign of an infection in an area

that is drained by the nodes The superficial group of nodes in the neck drain the skin of

the face and nose, scalp and external ear.

The submental nodes also drain the tip of the tongue.

Deeper regions of the head and neck drain into a deep groupof lymph nodes and are less palpable.

Other important landmarks the cartilages of the larynx and trachea

the thyroid gland is closely associated with the cricoidcartilage

the tracheal rings the carotid artery

carotid artery pulse can be felt by pushing lateral to the upperborder of the thyroid cartilage just under the anterior edge ofthe sternomastoid muscle.


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AnteriorTriangleofthe Neck In

Detail

Anterior Triangle

submental (smen)

submandibular (sm)

muscular-visceral

(mus)

carotid (car)

Posterior Triangle

occipital

supraclavicular (omoc

lavicular)

The neck is arbitrarily subdivided into two triangles by the sternocleidomastoid muscle:

Starting above the hyoid bone in the

anterior triangle, we have two small

triangles: submental and submandibular

(or digastric). We will start this study by

looking at the submandibular triangle firstthen the submental.


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The SubmandibularTriangle

Boundaries mastoid & mandible

above anterior belly of

digastric anteriorly(abd)

posterior belly of

digastric (pbd) stylohyoid posteriorly

(sh)


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The superficial (roof)

structures of the

submandibular region

are:

platysma

facial vein (fv)

cervical branch of

facial nerve (cbf)


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The Submental Triangle

located between the two

anterior digastric muscles

(abd).

Structures submental lymph node(s)

(ln) - drain the floor of the

mouth.

mylohyoid muscle (mh)

arise from the body of thehyoid bone and insert into

the mylohyoid line of the

inside of the mandible.

aids in swallowing and in

depressing the mandible.


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The Carotid Triangle

The boundaries of the

carotid triangle are:

posterior belly of

digastric muscle (pbd) superior belly of the

omohyoid muscle (so)

anterior border of

sternomastoid muscle(st)

Starting from the most superficial aspects of the carotid triangle, we will

point out the items that are related to it.


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Roof of the Carotid Triangle

The first layer, under

the skin and

superficial fascia

includes theplatysma, which

forms the roof of the

carotid triangle. Note

the location of thecarotid triangle in

purple.


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Veins of the Carotid Triangle

With the roof removed, here

are the boundaries of the

carotid triangle and the

superficial veins related to it:

common facial vein (cf) (within

carotid triangle)

Other structures near by:

retromandibular vein (rm)

posterior auricular vein (pav) facial vein (fv)

external jugular vein (ej)

anterior jugular vein (aj)


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Nerves within the Carotid Triangle

The nerves that enter thecarotid triangle and thatlie superficial to theinternal jugular vein,internal and externalcarotid arteries are: hypoglossal (XII)

C1 root of ansa cervicalis(C1)

C1 fibers running withhypoglossal nerve (nerveto thyrohyoid muscle (nth)

C2-C3 root of ansacervicalis

ansa cervicalis (ac)


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Nerves within the Carotid Triangle


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Floor of the carotid triangle

The floor is the the deepestaspect of the carotid triangle.

The muscles, at this level, arethe middle and lowerpharyngeal constrictors (mpc

and ipc).

The structures seen passingthrough this level are:

superior laryngeal nerve, abranch of the vagus its 2terminal branches

internal laryngeal (ilb--sensoryto upper part of the larynx)

external laryngeal (elb--motorto the cricoid muscle)


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MuscularorVisceral Triangle The muscular triangle has the

following boundaries: mid line of neck (1)

superior belly of omohyoid (2)

sternomastoid (3)

The muscles forming and

within the triangle are seen inimage labeled (these musclesare often called the strapmuscles, for obvious reasons: superficial layer

sternohyoid (sh) superior belly of omohyoid (oh)

deep layer

thyroid (th)

sternothyroid (st)


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Thyroidglandand

itsarterialsupply

When the strapmuscles are reflected,you can see the

thyroid gland (tg) withits arteries (superiorthyroid artery from theexternal carotid (sta)and the inferior

thyroid artery from thethyrohyoid trunk fromthe subclavian (ita).


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If the thyroid gland is

reflected laterally, the

structures making up thelarynx and trachea are

seen:

thyrohyoid membrane

(thm)

thyroid cartilage (Adam's

apple)(tc)

cricothyroid membrane

and ligament (ctm) cricoid cartilage (cc)

tracheal rings (tr)

Cartilagesandmembranes


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AnteriorViewofThyroid Gland

The thyroid gland ishidden under thesternohyoid andsternothyroid muscles

and consists of two lobesand an isthmus.

An occasional pyramidallobe extends upward nearthe mid line.

The inferior thyroid arteryis closely associated withthe recurrent laryngealnerve (rln).


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Deep SurfaceofThyroid Gland

Four small reddish-brownpea-sized glands may beseen on the deep surfaceof the thyroid gland.

These are the superiorand inferior parathyroidglands (ptg).

Also note the closerelationship of the

recurrent laryngealnerves to the thyroidgland and inferior thyroidartery (rln, ita).


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Most anterior

structures:

brachiocephalic vein

vertebral vein

internal jugular vein

subclavian vein

thoracic duct thymus gland


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Thenextlayercanbe

consideredtheartery-

nervelayer:

lung

vagusnerve

commoncarotidartery

subclavianartery

ansasubclavius

thyrocervicaltrunk

vertebralartery

internalthoracicartery

trachea

esophagus


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The upper lobe of the

lung (1) extends into

the neck region. This

is clinically importantfor anyone entering

this region surgically

since the lung can be

punctured if thesurgeon isn't careful.


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The posterior part of theroot of the neck is madeup of the anterior surface

of the body of the 1stthoracic vertebra with itsanterior longitudinalligament (in gray). Whenobserving this area, you

can see the nerves:

ventral ramus of C8

ventral ramus of T1

lower trunk of brachialplexus

stellate ganglion (inferiorcervical + 1st thoracicganglia)


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Table of Muscles

Muscle Origin Insertion Action Nerve Supply

Sternohyoid sternum hyoid ansa

OmohyoidSuprascapularnotch

hyoid ansa

SternothyroidBelowsternohyoid onmanubrium

Thyroidcartilageoblique line

ansa

Thyrohyoid Thyroidcartilageoblique line

hyoid C1-C2 (ansa)

Anterior BellyDigastric

-----intermediatetendon------

Inner surface ofmandile

Trigeminalnerve

Posterior BellyDigastric

Medial aspectof the mastoidprocess

-intermediatetendon-

Facial nerve

MylohyoidMylohyoid lineof mandible

Hyoid boneTrigeminalnerve

Hyoglossus Hyoid boneLateral side oftongue

hypoglossal

Stylohyoid Styloid process hyoid Facial nerve

unit 17 - anterior triangle of the neck

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