Lecture 8 and (9?): Anterior Triangle of The Neck

Question 1

What are the Clinically Relevant cases you might see involving the Anterior Triangle of the Neck?

Answer 1

• Thyroid examination
• Goitre
• Central venous catheterization
• Penetrating trauma
• Cricothyroidotomy/tracheostomy

Question 2

What is this?

Answer 2

Goitre

Question 3

Describe the fascia of the neck

Answer 3

Superficial fascia contains

• Thin platysma muscle, is innervated by the cervical branch of the facial nerve (VII).

Deep cervical fascia is organized into several distinct layers. These include:

• Investing layer surrounds all structures in neck (anteriorly surrounds infrahyoid muscles, forming posterior triangle);
• Prevertebral layer surrounds vertebral column and deep muscles associated with back
• Pretracheal layer encloses the viscera of the neck
• Carotid sheaths surround two major neurovascular bundles on either side of the neck (common carotid artery, internal carotid artery, internal jugular vein, vagus nerve)

Question 4

Which neck regions does the anterior triangle cover?

Answer 4

Anterior triangle covers level I-IV, VI-VII of neck lymphatic drainage.

Note that level II, III and IV regions cover sternocleidomastoid muscle.

Question 5

Where is the Anterior Triangle of the neck?

Answer 5

Anterior to the sternocleidomastoid

Whatever lies deep to the sternocleidomastoid is not part of the anterior or posterior triangle.

Question 6

Describe the venous draining of the anterior triangle

Answer 6

Internal jugular vein originates as a continuation of sigmoid sinus in the skull.

Aslo be aware of the Anterior jugular veins (not very important though)

Question 7

Name the muscles of the Anterior Triangle of the Neck

Answer 7

• Muscles of anterior triangle are divided into two groups based on their location in relation to hyoid bone:
  
  • Suprahyoid muscles (above so elevate hyoid) include
    
    • stylohyoid,
    • digastric,
    • mylohyoid,
    • geniohyoid.
  • Infrahyoid muscles (below so depress hyoid) include
    
    • sternohyoid,
      
      • From sternum to the hyoid
    • omohyoid,
      
      • More deep and more lateral to the sternohyoid
    • thyrohyoid,
    • sternothyroid.
• The innervation of the muscles of the anterior triangle of the neck in is important.

Question 8

Describe the Cervical Plexus

Answer 8

Transverse cervical nerve (C2, C3) emerges from beneath posterior border of sternocleidomastoid muscle and loops around to cross its anterior surface in a transverse direction. It is a cutaneous nerve in anterior triangle.

• Cervical plexus has motor and sensory components. (C1, 2, 3, 4)
• The thyrohyoid muscle has variable functions depending
  on which bone is fixed. It is innervated by fibers from
  the anterior ramus of C1 that travel with the hypoglossal
  nerve (XII] .
• There is a loop called the Ansa cervicalis, this only has a motor component (innervate infrahyoid muscle)
  
  • The ansa cervicalis is a loop of nerve fibers from cervical nerves C1 C2, C3 that innervate the “strap muscles” in the anterior triangle of the neck.
    • As hypoglossal nerve completes its descent and begins to pass forward across internal and external carotid arteries, some of cervical nerve fibers C1 leave it and descend between internal jugular vein and internal (then common) carotid arteries. These nerve fibers are superior root of ansa cervicalis and innervate superior belly of o_mohyoid muscle,_ and upper parts of sternohyoid and sternothyroid muscles.
    • Completing the loop is a direct branch from cervical plexus containing nerve fibers from C2 and C3. This is inferior root of ansa cervicalis. It descends either medial or lateral to the internal jugular vein before turning medially to join superior root. At this location, ansa cervicalis gives off branches that innervate the i_nferior belly of the omohyoid,_ and the lower parts of the sternohyoid and sternothyroid muscles.
• The sensory nerves in the posterior triangle is part of the cervical plexus.
  • Sensory comes right off the anterior rami
    
    • lesser occipital nerve
    • great auricular nerve
    • Supraclavicular
    • Transverse cranial nerve

Question 9

What innervates the thyrohyoid muscle?

Answer 9

The thyrohyoid muscle has variable functions depending
on which bone is fixed. It is innervated by fibers from
the anterior ramus of C1 that travel with the hypoglossal
nerve (XII] .

Question 10

What innervates the omohyoid muscle?

Answer 10

• As hypoglossal nerve completes its descent and begins to pass forward across internal and external carotid arteries, some of cervical nerve fibers C1 leave it and descend between internal jugular vein and internal (then common) carotid arteries. These nerve fibers are superior root of ansa cervicalis and innervate superior belly of omohyoid muscle, and upper parts of sternohyoid and sternothyroid muscles.
• Completing the loop is a direct branch from cervical plexus containing nerve fibers from C2 and C3. This is inferior root of ansa cervicalis. It descends either medial or lateral to the internal jugular vein before turning medially to join superior root. At this location, ansa cervicalis gives off branches that innervate the inferior belly of the omohyoid, and the lower parts of the sternohyoid and sternothyroid muscles.

Question 11

What innervatess the Sternothyroid muscle?

Answer 11

• As hypoglossal nerve completes its descent and begins to pass forward across internal and external carotid arteries, some of cervical nerve fibers C1 leave it and descend between internal jugular vein and internal (then common) carotid arteries. These nerve fibers are superior root of ansa cervicalis and innervate superior belly of omohyoid muscle, and upper parts of sternohyoid and sternothyroid muscles.
• Completing the loop is a direct branch from cervical plexus containing nerve fibers from C2 and C3. This is inferior root of ansa cervicalis. It descends either medial or lateral to the internal jugular vein before turning medially to join superior root. At this location, ansa cervicalis gives off branches that innervate the inferior belly of the omohyoid, and the lower parts of the sternohyoid and sternothyroid muscles.

Question 12

What innervates the sternohyoid muscle?

Answer 12

• As hypoglossal nerve completes its descent and begins to pass forward across internal and external carotid arteries, some of cervical nerve fibers C1 leave it and descend between internal jugular vein and internal (then common) carotid arteries. These nerve fibers are superior root of ansa cervicalis and innervate superior belly of omohyoid muscle, and upper parts of sternohyoid and sternothyroid muscles.
• Completing the loop is a direct branch from cervical plexus containing nerve fibers from C2 and C3. This is inferior root of ansa cervicalis. It descends either medial or lateral to the internal jugular vein before turning medially to join superior root. At this location, ansa cervicalis gives off branches that innervate the inferior belly of the omohyoid, and the lower parts of the sternohyoid and sternothyroid muscles.

Question 13

Describe the Thyroid

Answer 13

Thyroid gland is anterior in the neck, lying deep to sternohyoid, sternothyroid, and omohyoid muscles.

· It lies below and on either side of thyroid cartilage (lateral superior border).

· It has two lateral lobes with an isthmus, which connects the lobes. The isthmus crosses anterior surface of second and third tracheal cartilages.

Question 14

What are “strap” muscles?

Answer 14

The infrahyoid muscles (strap muscles) are a group of four pairs of muscles in the anterior (frontal) part of the neck. The four infrahyoid muscles are: the sternohyoid, sternothyroid, thyrohyoid and omohyoid muscles.

Question 15

What connects the 2 lobes of the thyroid?

Answer 15

isthmus. The isthmus crosses anterior surface of second and third tracheal cartilages.

Question 16

The isthmus crosses anterior surface of _____ and _____ tracheal cartilages.

Answer 16

The isthmus crosses anterior surface of second and third tracheal cartilages.

Question 17

Describe the Arterial supply of the Anterior Triangle of the Neck

Answer 17

Common Carotid Arteries

After crossing superior thoracic aperture or the root of the neck, right and left common carotid arteries ascends through neck either sides of trachea and esophagus within carotid sheath.

• Right common carotid artery originates from the brachiocephalic trunk. It is entirely in neck throughout its course.
• Left common carotid artery is a direct branch of arch of the aorta. It begins in thorax and passes superiorly to enter neck.

Common carotid artery has no branches through the neck. It divides into internal and external carotid arteries, and bifurcation is typically at the C3/4 vertebral level (C3 is the level of the hyoid bone and C4 is the upper border of the thyroid cartilage).

Internal Carotid Artery

Internal carotid artery has no branches in the neck and supplies most of the ipsilateral cerebral hemisphere.

• Internal carotid artery lies in the carotid sheath initially medial to internal jugular vein and anterior to vagus nerve.
• Its origin is dilated forming carotid sinus which contains baroreceptors (relay pressure measurements via IX to medulla). Carotid body with its chemoreceptors is usually found behind bifurcation of common carotid artery.

External Carotid Artery

External carotid artery gives off branches immediately after the bifurcation of the common carotid artery.

Branches of external carotid artery help to distinguish this vessel from internal carotid artery. Branches include superior thyroid artery (first branch), ascending pharyngeal artery, lingual artery, facial artery, occipital artery, posterior auricular artery, superficial temporal artery (terminal), maxillary artery (terminal).

Question 18

Describe the Venous Drainage of the Thyroid

Answer 18

• Three veins drain the thyroid gland (Fig. 8 . 1 7 5 ) :
  • The superior thyroid vein primarily drains the area
  supplied by the superior thyroid artery.
  • The middle and inferior thyroid veins drain the rest
  of the thyroid gland.
• Superior and middle drainages drain back to the Internal Jugular vein
• Inferior drains back to the Left brachiocephalic vein
  
  • ​Middle dainage depends on the individual. It can drain to the LBV

So it is important to know which part of the thyroid the cancer is found.

Question 19

What artery supplies the isthmus of the thyroid in 20-30% of the cases?

Answer 19

Ima.

If the person has this artery, it almost always comes out from the arch of aorta.

Question 20

Describe the Lymphatic Drainage of the Thyroid

Answer 20

Lymphatic drainage of the thyroid gland is to nodes
beside the trachea (paratracheal nodes) and to deep cervical
nodes_inferior to the omohyoid muscle along the i_nternal
jugular vein.

It drains to lymphatic region III, VI.

Question 21

Describe the innervation of the thyroid gland

Answer 21

Thyroid gland receives its innervation from autonomic nervous system.

·Parasympathetic fibres come from vagus nerve (via recurrent laryngeal nerve)

·Sympathetic fibres are distributed from the sympathetic trunk (middle cervical ganglion running with arteries).

Thyroid gland is closely related to recurrent laryngeal nerves. After branching from vagus nerve and looping around subclavian artery on the right and the arch of the aorta on left, recurrent laryngeal nerves ascend in a groove between trachea and esophagus. They pass deep to the posteromedial surface of the lateral lobes of the thyroid gland and enter the larynx by passing deep to the lower margin of the inferior constrictor of the pharynx.

Question 22

At what level does the sympathetic nerves come out of the spinal cord?

Answer 22

T1-L2

Travels via the sympathetic chain.

The middle one goes to the thyroid

Question 23

What are some important relations of the thyroid gland?

Answer 23

The relations of the thyroid gland are important when considering thyroidectomy (whether subtotal or total).

• Surgeons need to be aware of possible anatomical variations and complications related to such procedures.
• These complications include r_ecurrent or superior laryngeal nerve_ injury and parathyroid insufficiency from inadvertent removal.
• On each side of the thyroid, there is the c_arotid sheath_ (with internal jugular, common carotid and vagus).
• Behind the isthmus, there is the trachea (2nd and 3rd rings)
• Behind the trachea, you have the oesophagus
• Between the eosophagus and the trachea, there are the recurrent laryngeal nerves.

Question 24

Label

Answer 24

1) Isthmus
2) Left lobe of thyroid
3) Left internal jugular vein
4) Right internal jugular vein
5) Right lobe thyroid

Question 25

Briefly describe the embyrology of the thyroid gland

Answer 25

The thyroid gland arises as a median outgrowth from _foramen cecum_ at _base of tongue_. (and then moves down) _Thyroglossal duct_ marks the path of migration (passes hyoid bone) to its final adult location of thyroid gland, anterior to trachea in the root of neck. * The process begins at the third week and is completed by the _seventh week_ of development. * Thyroglossal duct usually disappears early in development but cysts, fistulae or ectopic thyroid tissue may persist in the midline and distinctively move with swallowing or protruding the tongue. In some cases bits of tissue may stay in the tongue (called **_Lingual thyroid_**) or anywhere between the tongue and the thyroid (called **_Accessory thyroid tissue_**). If it's in the neck below the hyoid bone, it's called the **_Cervical thyroid_**. But if it's on top of the thyroid, it's called the **_Pyramidal thyroid_**.

Question 26

Describe the Arterial supply of the Thyroid

Answer 26

Arterial Supply Two major arteries supply thyroid gland, which are superior thyroid and inferior thyroid arteries. * _Superior thyroid artery_ originates from external carotid artery (its first branch in the neck). It runs downward to reach upper pole of lateral lobe where it divides into anterior and posterior glandular branches. * _Inferior thyroid artery_ originates from thyrocervical trunk (a branch of first part of subclavian artery). It runs upward behind carotid sheath to reach lower pole of lateral lobe where it divides into inferior and ascending branch.

Question 27

During Thyroid development.. In some cases bits of tissue may stay in the tongue (called\_\_\_\_\_) or anywhere between the tongue and the thyroid (called \_\_\_\_\_\_\_). If it's in the neck below the hyoid bone, it's called the\_\_\_\_\_\_. But if it's on top of the thyroid, it's called the \_\_\_\_\_\_\_.

Answer 27

In some cases bits of tissue may stay in the tongue (called **Lingual thyroid**) or anywhere between the tongue and the thyroid (called **Accessory thyroid tissue**). If it's in the neck below the hyoid bone, it's called the **Cervical thyroid**. But if it's on top of the thyroid, it's called the **Pyramidal thyroid**.

Question 28

What is the significance of the Thyroglossal duct

Answer 28

The thyroglossal duct is an epithelium-lined _connection_ between the _foramen caecum_ and the _thyroid_ that develops during the descent of the thyroid. It usually involutes in the 8th-10th week of gestation. In some cases, when someone comes in with thyroid problems and you do a scan, you may see lots of tissues looking red and black anywhere down the thyroglossal duct Additionally, in some people, it may not close. So if they have food, it may go down the thyroglossal duct and they cannot breathe properly.

Question 29

What are the boarders of the Anterior Triangle of the Neck

Answer 29

Anterior triangle of the neck is formed by the anterior border of the _sternocleidomastoid_ muscle laterally, the _inferior border of the mandible_superiorly, and the _midline of the neck_ medially (C).

Question 30

Describe the IX cranial nerve

Answer 30

Glossopharyngeal nerve (IX) It leaves the skull through the jugular foramen and lies deep to the styloid apparatus. It then runs down and forward between the internal and external carotid arteries, curves around the lateral border of the stylopharyngeus and continues in an anterior direction to reach the base of the tongue.

Question 31

Describe the 10th cranial nerve

Answer 31

Vagus nerve (X) It leaves the skull through the jugular foramen between CN IX and XI. It travels downward in the carotid sheath, between the internal carotid artery and internal jugular vein. At the root of the neck it passes in front of the subclavian artery and behind the subclavian vein to enter the mediastinum.

Question 32

Describe the cranial nerve XI

Answer 32

Accessory nerve (XI) It leaves the skull through the middle part of the jugular foramen posterior to CN X, runs posterolaterally either medial or lateral to the internal jugular vein, crosses the transverse process of the atlas and passes medial to the styloid process and posterior belly of digastric to perforate the sternocleidomastoid muscle and reach the posterior triangle of the neck.

Question 33

Describe the XII cranial nerve

Answer 33

It leaves the skull through the hypoglossal foramen, passes between the internal carotid artery and internal jugular vein and crosses three arteries (occipital, external carotid and lingual arteries) deep to the posterior belly of digastric to reach the tongue. A branch from the anterior rami of C1 hitchhikes with it. This branch innervates some of the suprahyoid muscles (thyrohyoid and geniohyoid).

Question 34

Describe the layers of the Cervical fascia

Answer 34

Investing fascia Visceral fascia Pretracheal fascia Prevertebral fascia Carotid sheath

Question 35

What makes up the Superhyoid muscle

Answer 35

Suprahyoid muscles (above so elevate hyoid) include _stylohyoid_, _digastric_, _mylohyoid_, and _geniohyoid_.

Question 36

Label

Answer 36

1) Stylohyoid muscle 2) Posterior belly of digastric muscle 3) Mylohyoid muscle 4) Posterior belly of digastric muscle 5) Sylohyoid muscle 6) Anterior belly of digastric muscle 7) Geniohyoid muscle

Question 37

Describe the innervations of the Suprahyoid muscles

Answer 37

* **Mylohyoid** arises from mylohyoid line of mandible to hyoid bone. It is superior to anterior belly of diagastric and innervated by mandibular division of _trigeminal nerve (V3)._ * **Geniohyoid** arises from inferior mental spine of mandible to hyoid bone. It is deepest muscle in this layer and not generally considered anterior triangle muscle. It is innervated by a branch from _anterior ramus of C1_ carried along _hypoglossal nerve (XII)._ * **Stylohyoid** arises from styloid process to hyoid bone, and it is innervated by _facial nerve (VII)_ * **Digastric muscle** has two bellies connected by a tendon via hyoid bone: * *Anterior belly* arises from mandible, innervated by mandibular division of _trigeminal nerve (V3)_ * *Posterior belly* arises from mastoid process, innerved by _facial nerve (VII)_

Question 38

Describe the Innervation to the Infrahyoid (strap) muscles

Answer 38

* **Thyrohyoid** originates at thyroid cartilage running to hyoid bone. It is deep to superior parts of omohyoid and sternohyoid. It is innervated by anterior ramus of C1 that travel with hypoglossal nerve (XII). * **Omohyoid** consists of two bellies with an intermediate tendon via clavicle in both posterior and anterior triangles. It is innervated by anterior rami of C1 to C3 through ansa cervicalis. * Inferior belly (C2/3) begins on superior border of scapula, passes forward upward across posterior triangle and ends at tendon. * Superior belly (C1) begins at tendon and ascends to hyoid bone, lateral to sternohyoid. This is part of anterior triangle. * **Sternohyoid** originates from sternum to hyoid bone. It is innervated by anterior rami of C1 to C3 * **Sternothyroid** originated from sternum to thyroid cartilage. It lies beneath sternohyoid and in continuity with thyrohyoid. It is innervated by anterior rami of C1 to C3.

Question 39

Describe the Venous drainage of the _anterior triangle_

Answer 39

* _Internal jugular vein_ originates as a continuation of sigmoid sinus in the skull. * It exits the skull through the jugular foramen together with cranial nerves IX, X and XI and enters the carotid sheath. * It joins _subclavian vein_ to form brachiocephalic vein behind sternoclavicular joint. * It receives tributaries from _inferior petrosal sinus; facial, lingual, pharyngeal, occipital, superior thyroid, middle thyroid_ veins. * _External jugular vein_ * \*\* need to know \*\* * The _posterior auricular vein_ joins the _retromandibular_ vein and forms the external jugular vein. * Later the facial vein may drain here. * _Anterior Jugular vein_

Question 40

(generally) \_\_\_\_\_ artery supplies the neck \_\_\_\_\_ artery supplies the head

Answer 40

Neck is supplied by the EXTERNAL cartoid the head is supplied by the INTERNAL carotid (internal carotid is in the carotid sheath)

Question 41

How is the external jugular vein formed?

Answer 41

The _posterior auricular vein_ joins the _retromandibular vein_ and forms the external jugular vein.

Question 42

What forms the Internal Jugular Vein

Answer 42

It receives tributaries from _inferior petrosal sinus_; _facial_, _lingual_, _pharyngeal_, _occipital_, _superior thyroid_, _middle thyroid veins_.

Question 43

Which nerves exit the skull via the Jugular Foramen

Answer 43

CN 9, 10, 11

Question 44

Describe the Central Vein Catherterization

Answer 44

Central vein catheterization is between two heads of sternocleidomastoid muscle. (into IJV)

Question 45

*Note that ______ nerve is closer to midline, while _____ nerve is more lateral (both over scalene muscle).*

Answer 45

*Note that **phrenic** nerve (C3/4/5) is closer to midline, while **vagus** nerve is more lateral (both over scalene muscle).*

Question 46

The Accessory nerve runs \_\_\_\_\_\_\_

Answer 46

(runs within carotid sheath, perforated it and into posterior triangle

Question 47

An elderly man with cervical lymphadenopathy in the posterior triangle has had a lymph node middle of the triangle removed. What are the possible lymph node biopsy-related injuries?

Answer 47

* _Accessory nerve_ damage/cut -\> test by asking patient to fully raise shoulder/shrug their shoulders * _Cutaneous branches of the cervical plexus_ -\> test by assessing sensation of the neck

Question 48

An elderly lady presents to ED with hypovolemic shock after a car accident. A central-vein catheter is inserted through the posterior triangle. What are the possible CVC-related injuries (both direct and indirect)?

Answer 48

* _Accessory nerve_ damage/cut * Cutaneous branches of the c_ervical plexus_ * _Bleeding within carotid sheath_ -\> puts pressure on vagus nerve and common carotid artery leading to cranial nerve symptoms

Question 49

Together with branches of the \_\_\_\_\_\_\_arteries , the recurrent laryngeal nerves are clearly related to, and may pass through ligaments, one on each side of the, bind the _thyroid gland to the trachea_ and to the \_\_\_\_\_\_ cartilage of the larynx. These relationships need to be considered when surgically removing or manipulating the thyroid gland.

Answer 49

Together with branches of the i_nferior thyroid arteries ,_ the _recurrent laryngeal nerves_ are clearly related to, and may pass through ligaments, one on each side, that bind the thyroid gland to the trachea and to the _cricoid_ cartilage of the larynx. These relationships need to be considered when surgically removing or manipulating the thyroid gland.

Question 50

What are the contents of the Anterior Triangle?

Answer 50

The main contents of the carotid triangle are the _common carotid arter_y (which bifurcates within the carotid triangle into the external and internal carotid arteries), the i_nternal jugular vein_, and the **_hypoglossa_**l and v_agus nerves._