The Anterior and Posterior Triangles of the Neck

Anterior Triangle of the Neck

BONY SKELETON OF THE NECKLike other regions of the body, the neck has a central bony skeletal core upon which other structures attach or are related. The bones of the neck consist of the base of the skull and the 7 cervical vertebrae.

• If we take a look at the base of the skull, the major parts that are related to the upper neck are the:– Foramen magnum – Occipital condyle (articulates

with the superior process of the atlas.

– External occipital protuberance – Mastoid process

• 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 arterial supply to the brain and brain stem, the vertebral artery.

• The first cervical vertebra is the atlas and is considered an atypical cervical vertebra because it has no body or spinous process. It articulates with the occipital condyles of the skull above it and with the superior articular processes of the axis below it. It also articulates with the dens of the axis below. If viewed from above, you can identify the following parts of the atlas: – Anterior arch – Anterior tubercle – Superior articular process

(articulate with the occipital condyle of the skull)

– Foramen transversarium – Transverse process – Posterior arch – Posterior tubercle – Vertebral canal (continuous with the

foramen magnum at the base of the skull). The brain stem continues inferiorly as the spinal cord at the margin of the foramen magnum.

• The axis is the second cervical vertebra. This vertebral is also called an atypical vertebra because it has an upward projection called the dens that articulates with the inner aspect of the anterior arch of the atlas just posterior to the anterior tubercle. Some of the identifiable parts are the: – dens – body – superior articular process – transverse process with its

vertebral foramen – pedicle – lamina – bifid spine

• The 3rd, 4th, 5th, and 6th cervical vertebrae are known as the typical cervical vertebrae because they all have the same characteristics and except for the foramen for the vertebral artery similar to other typical vertebrae 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 of

a groove that carries a cervical spinal nerve and, of course the foramen for the vertebral artery)

• 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, it enters the transverse foramen of the 6th cervical vertebra bypassing the 7th

– may not have a bifid spinous process– the spinous process of the 7 cervical vertebra is

longer than the other cervical vertebrae – it is not buried under the ligamentum nuchae of the

neck so it is easy to see and to palpate and is called the vertebra prominens

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

Anterior Neck

• Common carotid artery (cc) • Internal carotid artery (ic) • External carotid artery (ec) • Carotid sinus

Major Landmarks

• Superficial structures from the lateral view of the neck. – sternomastoid – trapezius – occipital lymph nodes (on) – retroauricular lymph nodes

(ran) – superficial cervical lymph

nodes (scn) – submental lymph nodes

(smn) – buccal lymph nodes (bn) – parotid lymph nodes (pn) – submandibular lymph

nodes (not labeled but uner angle of mandible)

• 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 group

of lymph nodes and are less palpable.

• Other important landmarks– the cartilages of the larynx and trachea– the thyroid gland is closely associated with the cricoid

cartilage – the tracheal rings – the carotid artery

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

Anterior Triangle of the Neck In Detail

• Anterior Triangle– submental (smen) – submandibular (sm) – muscular-visceral

(mus) – carotid (car)

• Posterior Triangle– occipital – supraclavicular 

(omoclavicular)

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 first then the submental.

Triangles within the Anterior Triangle of the Neck

The Submandibular Triangle

• Boundaries – mastoid & mandible

above – anterior belly of

digastric anteriorly (abd)

– posterior belly of digastric (pbd)

– stylohyoid posteriorly (sh)

• The superficial (roof) structures of the submandibular region are:   – platysma – facial vein (fv) – cervical branch of

facial nerve (cbf)

• Removal of the superficial structures displays the submandibular salivary gland itself.

• contents of the submandibular triangle are structures passing through: – facial artery (fa) – lingual nerve and

submandibular ganglion (ln) – submandibular duct (smd) – lingual artery (la) – hypoglossal nerve (XII)

• the lingual nerve and submandibular duct pass through a gap between the hypoglossal (hg) and mylohyoid (mh) muscles

• the lingual artery passes deep to the hyoglossus muscle.

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 the hyoid bone and insert into the mylohyoid line of the inside of the mandible.

• aids in swallowing and in depressing the mandible.

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.

Roof of the Carotid Triangle

• The first layer, under the skin and superficial fascia includes the platysma, which forms the roof of the carotid triangle. Note the location of the carotid triangle in purple.

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)

Nerves within the Carotid Triangle

• The nerves that enter the carotid triangle and that lie superficial to the internal jugular vein, internal and external carotid arteries are: – hypoglossal (XII) – C1 root of ansa cervicalis

(C1) – C1 fibers running with

hypoglossal nerve (nerve to thyrohyoid muscle (nth)

– C2-C3 root of ansa cervicalis

– ansa cervicalis (ac)

Nerves within the Carotid Triangle

Reflection of sternomastoid and removal of common facial vein

• cca-common carotid artery eca-external carotid artery

• sta-supterior thyroid artery

• oa-occipital artery • la-lingual artery • fa-facial artery • ica-internal carotid artery

Arteries in the Carotid Triangle

Floor of the carotid triangle

• The floor is the the deepest aspect of the carotid triangle.

• The muscles, at this level, are the middle and lower pharyngeal constrictors (mpc and ipc).

• The structures seen passing through this level are: – superior laryngeal nerve, a

branch of the vagus its 2 terminal branches

– internal laryngeal (ilb--sensory to upper part of the larynx)

– external laryngeal (elb--motor to the cricoid muscle)

Muscular or Visceral 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 in image labeled (these muscles are often called the strap muscles, for obvious reasons: – superficial layer

• sternohyoid (sh) • superior belly of omohyoid (oh)

– deep layer • thyroid (th)

– sternothyroid (st)

Thyroid gland and its arterial supply

• When the strap muscles are reflected, you can see the thyroid gland (tg) with its arteries (superior thyroid artery from the external carotid (sta) and the inferior thyroid artery from the thyrohyoid trunk from the subclavian (ita).

• If the thyroid gland is reflected laterally, the structures making up the larynx and trachea are seen: – thyrohyoid membrane

(thm) – thyroid cartilage (Adam's

apple)(tc) – cricothyroid membrane

and ligament (ctm) – cricoid cartilage (cc) – tracheal rings (tr)

Cartilages and membranes

Anterior View of Thyroid Gland

• The thyroid gland is hidden under the sternohyoid and sternothyroid muscles and consists of two lobes and an isthmus.

• An occasional pyramidal lobe extends upward near the mid line.

• The inferior thyroid artery is closely associated with the recurrent laryngeal nerve (rln).

Deep Surface of Thyroid Gland

• Four small reddish-brown pea-sized glands may be seen on the deep surface of the thyroid gland.

• These are the superior and inferior parathyroid glands (ptg).

• Also note the close relationship of the recurrent laryngeal nerves to the thyroid gland and inferior thyroid artery (rln, ita).

Clinical Considerations

• The cricothyroid ligament and membrane are frequently pierced in emergency situations to open the airway.

• It has been known that an empty ball-point pen or a hollow stem has been used in the field to save lives, where an air passage has been closed above this region.

Structures Found At the Root of the Neck

• After the sternoclavicular joint is disarticulated the structures located at the root of the neck can be identified.

• The root of the neck is bounded by the manubrium of the sternum anteriorly, the first rib laterally and the first thoracic vertebra posteriorly.

• All structures passing from the head through the neck to lower regions pass through this area as well as structures arising in the thoracic cavity and passing out through this region.

• Most anterior structures:

• brachiocephalic vein • vertebral vein • internal jugular vein • subclavian vein • thoracic duct • thymus gland

• The next layer can be considered the artery-nerve layer:  

• lung • vagus nerve • common carotid artery • subclavian artery • ansa subclavius • thyrocervical trunk • vertebral artery • internal thoracic artery • trachea • esophagus

• The upper lobe of the lung (1) extends into the neck region. This is clinically important for anyone entering this region surgically since the lung can be punctured if the surgeon isn't careful.

• The posterior part of the root of the neck is made up of the anterior surface of the body of the 1st thoracic vertebra with its anterior longitudinal ligament (in gray). When observing this area, you can see the nerves:  

• ventral ramus of C8 • ventral ramus of T1 • lower trunk of brachial

plexus • stellate ganglion (inferior

cervical + 1st thoracic ganglia)

Table of Muscles

Muscle Origin Insertion Action Nerve Supply

Sternohyoid sternum hyoid ansa

OmohyoidSuprascapular notch

hyoid ansa

SternothyroidBelow sternohyoid on manubrium

Thyroid cartilage oblique line

ansa

ThyrohyoidThyroid cartilage oblique line

hyoid C1-C2 (ansa)

Anterior Belly Digastric

-----intermediate tendon------

Inner surface of mandile

Trigeminal nerve

Posterior BellyDigastric

Medial aspect of the mastoid process

-intermediate tendon-

Facial nerve

MylohyoidMylohyoid line of mandible

Hyoid boneTrigeminal nerve

Hyoglossus Hyoid boneLateral side of tongue

hypoglossal

Stylohyoid Styloid process hyoid Facial nerve