Neck 5: Area under the SCM

Question 1

Carotid sheath definition

Answer 1

a tubular sleeve composed of areolar tissue of investing, pretracheal, prevertebral and visceral cervial fascial origins, extending from the base of the skull through the root of the neck, which encircles the common and internal carotid arteries, internal jugular vein, vagus nerve and its associated deep cervical lymph nodes. At its superior most extent, it is associated with other structures: CNs IX, X, XI which exit the jugular foramen, CN XII, the hypoglossal nerve, which exits its own foramen in close proximity to the carotid sheath and the superior cervical sympathetic ganglion. Inferiorly, the sheath fuses with the adventitias of the great vessels and fibrous pericardium.

Question 2

Generalized contents of carotid sheath

Answer 2

common and internal carotid arteries
internal jugular vein
vagus nerve
ansa cervicalis: superior root inside seath, inferior root on its lateral surface
deep cervical lymph nodes

Question 3

Generalized relationships of the carotid sheath

Answer 3

1. Deep to the SCM; apprximately follows its anterior border
2. Within the sheath, the artery lies medial and anterior while the vein is lateral and somewhat posterior
3. The vagus nerve descends in the posterior groove between the two vessels
4. The ansa cervicalis of the cervical plexus lies within the carotid sheath lateral to the common and internal carotid arteries (superior root), crosses the internal jugular vein anteriorly and courses superiorly, laterally and posteriorly on its surface (inferior root).
5. Deep cervical lymph nodes form a chain along the internal jugular vein and may be embedded within the sheath itself.

Question 4

Common carotid artery (in the sheath)

Answer 4

Left side longer than right; right originates from brachiocephalic split, left from the arch of the aorta

Extends approximately to the superior horn of thyroid cartilage opposite CV3 where it terminates as internal and external carotid arteries.

Usually has no branches although sometimes the superior thyroid artery, during development, will “slide” down onto the common carotid (16%)

Carotid sinus and carotid body

Question 5

Carotid sinus

Answer 5

located at the dilated sital common carotid and proximal internal carotid; pressure receptor (increase in P = decrease in HR)

NOTE: Afferents travel mainly in the carotid sinus nerve (CNIX); minor routes include carotid branches of the vagus and cervical sympathetic trunk.

Question 6

Carotid body

Answer 6

located at the carotid bifurcation; chemoreceptor- senses changes in oxygen tension (decrease in O2 = increase in rate and depth of respiration)

NOTE: Afferents travel mainly in the carotid sinus nerve (CNIX); minor routes include carotid branches of the vagus and cervical sympathetic trunk.

Question 7

Internal carotid artery

Answer 7

ascends within the carotid sheath to the base of the skull where it enters the carotid canal. Prior to entering the canl, it has NO branches. Intracranially, it supplies the orbit and brain.

Question 8

External carotid artery- course and relations

Answer 8

(although not in the sheath, considered here)

branches from teh common carotid in the carotid triangle near the superior horn of hte thyroid cartilage where it usually gives off its first four branches: superior thyroid, ascending pharyngeal, lingual and facial. As it ascends, it is crossed laterally by the posterior belly of the digastric and stylohyoid muscles where it gives off its fifth and sixth branches: occipital and posterior auricular branches. At the point of origin of the occipital artery, the external carotid is crossed laterally by the hypoglossal n. (CN XII) as it passes through the carotid sheath en route to the tongue. Ascending medial to the mandible in the deep parotid space, the external carotid artery terminates near the neck of hte mandible by bifurcating into the maxillary and superficial temporal arteries.

Question 9

Clinical note re: surgery through carotid triangle

Answer 9

Surgical approach through the carotid triangle (boundaries: anterior border of SCM, posterior border of sup. belly of omohyoid, inferior border of post. belly digastric) provides access to the carotid bifurcation, internal jugular v. vagus and hypoglossal nn., and the sympathetic trunk. Manipulation of the vagus and recurrent laryngeal nn. during this approach can lead to protracted changes in the voice as these nerves innervate the muscles of the larynx.

Question 10

Clinical note: carotid endarterectomy

Answer 10

The aforementioned surgical approach is utilized to remove atherosclerotic plaque which may gather at the branch point of the internal and external carotid aa. from the common carotid artery where turbulent blood flow is increased causing injury to the endothelium with deposition of fat, cholosterol, clotted blood, and eventually calcium. The removal of the accumulated plaque, carotid endarterectomy, eliminates the stenotic segment, which if left in situ, can lead to transient ischemic attacks (decreased blood flow to the brain) and possible micro emboli formation leading to strokes.

Question 11

Branches of the External Carotid artery

Answer 11

Superior thyroid a.
–> superior laryngeal, a., anterior branch, posterior branch

Ascending pharyngeal a.
Lingual a.
Facial a.
Occipital a. 
Posterior Auricular a.

Question 12

Superior thyroid artery

Answer 12

1st branch of external carotid

courses along the superior medial margin of the thyroid gland

Major branches:
a. Superior laryngeal a.- pierces the thyrohyoid membrane with the internal laryngeal n. (vagus) to provide branches to the interior of the larynx

b. Anterior branch- branches to the anterior portion of the thyroid gland; anastomoses with opposite counterpart
c. Posterior branch- branches to the posterior portion of gland; anastomoses with branches of the inferior thyroid artery.

Question 13

Ascending pharyngeal a.

Answer 13

arises from the medial aspect of the external carotid usually near the bifurcation. It travels in the connective tissue lateral to the pharyngeal wall just medial to the internal carotid artery and courses STRAIGHT to the base of the skull. Its branches include:
pharyngeal
palatine a. (tonsillar branch)
inferior tympanic a.
Meningeal a.

Question 14

Lingual a.

Answer 14

may arise from a common trunk with the facial artery usually opposite the greater horn of the hyoid. It passes deep to the posterior border of the hyoglossus muscle to enter the tongue where it provides the following branches:
dorsal lingual
deep lingual
sublingual

Question 15

Facial a.

Answer 15

may arise from a common trunk with the lingual artery or just above it singly. It courses obliquely anteriorly deep to the posterior belly of the digastric and stylohyoid and grooves the deep surface of the submandibular gland. It leaves the submandibular region by coursing around the sharp inferior border of the mandible at the anterior edge of the attachment of the masseter muscle and enters the face. Its submandibular branches include:
Tonsillar a.
ascending palatine a.
glandular a.
muscular a.
submental a.

Question 16

Occipital a.

Answer 16

passes posteriorly from the external carotid at the inferior border of the posterior bellly of the digastric to pass between the transverse processs of the atlas and the mastoid process (which it grooves). It becomes superficial at the superior extent of the posterior triangle (apex) where it pierces the cervical fascia at the point where the trapezius and SCM come together. From there, it enters the scalp and parallels the course of the greater occipital n. Its significant branches include:
SCM branch
Meningeal branch
Auricular a.
mastoid a.
Descending branch (to deep neck)

Note: the hypoglossal N. crosses the occipital a. at its origin from the external carotid.

Question 17

Posterior auricular a.

Answer 17

passes posteriorly from the external carotid at the superior border of the posterior belly of the digastric to course posterior to the auricle (external ear) posterior to the external acoustic meatus and anterior to the mastoid process. Its branches include:
muscular branches to surrounding musculature
parotid branches
stylomastoid (to middle ear)
auricular (to scalp)
occipital (to scalp)

Note- remaining 2 will be saved for later.

Question 18

Clinical note re: ligation of external carotid

Answer 18

Ligation of the external carotid is needed to stem the flow of blood from deeper branches which are not surgically accessible without damaging other major structures, i.e. during dcarotid endarterectomy. In these cases, enough blood reaches the vascular fields on the ligated side by filling anastomotic vessels communicating from one side to the other. i.e., arteries of the scalp, face and deep face, by reversing the flow in the arteries on the ligated side.

Question 19

Internal jugular veins

Answer 19

Largest vein of the head and neck
receives blood from the face, neck and the brain via the dural venous sinuses
Begins as a dilatation (superior jugular bulb) at the jugular foramen located at the junction of the temporal and occipital bones
As it descends in the carotid sheath, its relationship to the carotid arteris changes, such that superiorly it lays posterolateral, in mid-course lateral and inferiorly lays anterolateral.
Ends by dilating to form an inferior bulb that lies posterior to the sternoclavicular joint where it joins the subclavian vein to form the brachiocephalic vein. Along its course, it receives these tributaries:
1. Occipital vv.
2. Pharyngeal vv.
3. Lingual v.
4. Facial v. as common facial v.
5. Superior and middle thyroid vv.

Question 20

Clinical note: internal jugular vein puncture

Answer 20

For diagnostic purposes, the RIGHT internal jugular vein can be accessed by inserting a needle/ catheter inferiorly at the apex of the triangle between the clavicular and sternal heads of the SCM with the needle inserted approximately a finger’s breadth lateral to the common carotid pulse at a 30 degree angle aimed inferiorly toward the ipsilateral nipple.

Question 21

Vagus Nerve innervation

Answer 21

Largest cranial nerve
parasympathetic to heart, lungs, and most of digestive system (GVE-P)
Motor to striated muscles of the pharynx, palate, larynx, and proximal 1/3 of esophagus (SVE)
General sensation (GVA) to carotid body, epiglottis, larynx, respiratory system, GI tract to terminal colon, and (GSA) to external ear, external auditory meatus, external surface tympanic membrane and posterior cranial fossa dura mater.
Taste to the epiglottic portion of the tongue (SVA)

Question 22

Vagus nerve origin and course

Answer 22

exits brainstem at medulla
exits skull via jugular foramen
courses in the carotid sheath posteriorly between the carotids (internal and common) and internal jugular vein
Enters the thorax on the right side between the subclavian a and the right brachiocephalic vein; on the left between the junction of the left common carotid with the left subclavian artery and the left brachiocephalic vein.

Question 23

Note: vagus nerve communication

Answer 23

While in the superior retropharyngeal retion, the vagus communicates with CNs IX, XI and XII, the superior cervical ganglion and spinal nerves C1 and C2.

Question 24

Branches of the vagus

Answer 24

meningeal- to dura of posterior cranial fossa (GSA)
auricular- to posterior surface of pinna, auditory canal and external surface of tympanic membrane (GSA)
Pharyngeal- component of the pharyngeal plexus; provides branches to majority of the muscles of the pharynx and soft palate (SVE)
Nerve to the carotid body- from pharyngeal branch; afferent limb from O2 chemoreceptors in carotid bifurcation (GVA)
Superior laryngeal n.- passes downward and obliquely forward from the superior portion of the vagus n. to the larynx traveling medial to the carotid sheath. (internal and external branches)

Question 25

Branches of the superior laryngeal n.

Answer 25

Internal branch (SVA, GVA, GVE-P)- pierces the thyrohyoid membrane with the superior laryngeal branch of the superior thyroid artery to provide:

1. sensory fibers of taste (SVA) to the epiglottic valeculae
2. General sensation (GVA) to the epiglottis, aryepiglottic folds, entire internal portion of the larynx above glottis
3. Parasympathetic innervation (GVE-P) t mucous glands of the entrire internal portion of the larynx above glottis.

External branch (SVE)- courses lateral to the pharynx and larynx on the inferior constrictor muscle accompanied by the superior thyroid artery. At the inferior border of the thyroid cartilage, it courses medially to innervate the cricothyroid muscle and inferior constrictor muscle.

Question 26

Recurrent laryngeal n. (SVE, GVA, GVE-P)

Answer 26

passes superiorly from an inferior position or otherwise “recurs” near the root of hte neck on the right or from the upper thorax on the left. On the right side, this nerve recurs around the subclavian artery; on the left, around the aortic arch at the ligamentum arteriosum. They BOTH eventually reach the larynx by coursing in the connective tissue interval between the trachea and esophagus posterior to the cricothyroid joint to provide:

1. motor fibers (SVE) to all intrinsic muscles of hte larynx EXCEPT the cricothyroid
2. General sensation fibers (GVA) to the entire mucosa inferior to the true vocal folds
3. secretory fibers (GVE-P) to the entire mucosa inferior to the true vocal folds.

NOTE: Once the recurrent laryngeal nerves pass into the larynx, they are referred to as inferior laryngeal nerves.

Other branches of the recurrent laryngeal nerves include:
cardiac banches to the deep cardiac plexus
branches to muscles and glands of the trachea and esophagus
pharyngeal branches to the inferior constrictor muscle

Question 27

Deep Cervical Lymph Nodes

Answer 27

associated with the carotid sheath along the course of the internal jugular vein
divided into two groups by the passage of the omohyoid muscle: superior above, inferior below

Question 28

Superior deep cervical lymph nodes

Answer 28

located in the carotid triangle superior to the superior belly of the omohyoid
composed of retropharyngeal, deep parotid, jugulodigastric and jugulo-omohyoid nodes
receive efferent lymph channels from superficial lymph nodes of the face and neck, as well as drainage from deeper areas of the head via direct efferents to the nodes just listed
lymph from superior deep nodes drains to inferior deep nodes

Question 29

Inferior deep cervical lymph nodes

Answer 29

located inferior to the superior belly of the omohyoid muscle
composed of only a few nodes located in a supraclavicular position; may extend into the omoclavicular triangle

Receive lymph from:

a. superficial cervical lymph nodes
b. superior deep cervical nodes
c. occipital lymph nodes
d. accessory chain of the posterior triangle
e. transverse cervical nodes of the posterior triangle
f. juxtavisceral nodes of the anterior triangle (nodes parallel to the larynx and trachea: infrahyoid, pre-laryngeal, pre-tracheal, paratracheal)

Question 30

Jugular lymph trunks

Answer 30

formed by efferents of the superior and inferior deep cervical nodes
on the left side, drain to the THORACIC DUCT
On the right side, joins with the subclavian and right broncho-mediastinal lymph trunks to form the RIGHT LYMPHATIC DUCT which enters the venous system at teh right jugulovenous angle formed by the subclavian and internal jugular veins.

Question 31

Clinical note: cancer

Answer 31

In cases where metastatic cancer cells have been discovered in supraclavicular nodes, surgeons may perform a radical neck dissection removing en bloc all of the deep cervical lymph nodes and surrounding tissue. Since the aim is the removal of all traces of the cancer, superficial structures, including the cutaneous branches of the cervical plexus are removed, while the deeper more important structures such as the brachial plexus, vagus and phrenic nerves are spared.

Question 32

Hypoglossal Nerve CN XII

Answer 32

(GSE)
Note: although the hypoglossal nerve is not contained within the carotid sheath, it is associated with it and courses through the area we are now considering, i.e. area deep to the SCM.

Exits the skull via the hypoglossal canal medial to the internal jugular v. and internal carotid a., but still close enough to be invested in fibers of the carotid sheath.
It descends posterior to the vagus n. and as it passes lateral to the transverse process of the atlas it communicates with CN X, the superior cervical sympathetic ganglion and ventral rami of spinal nerves C1 and C2 (see cervical plexus)

As the hypoglossal nerve descends, it courses between the internal jugular v. and the external carotid a. at the origin of the occipital a.

It enters the submandibular triangle deep to the posterior belly of the digastric muscle just above the hyoid bone Here it passes between the mylohyoid and hyoglossus muscles to enter the tongue.

Question 33

Cervical Plexus general considerations

Answer 33

composed of ventral rami of C1-C4
innervates the deep cervical muscles of the vertebral column, infrahyoid musculature and the diaphragm
Provides innervation to sensory dermatomes of the lateral head, neck, superolateral shoulder and upper anterior thorax
Distributes postganglionic sympathetic innervation to all areas supplied by the cervical plexus

Question 34

Sensory nerves of the cervical plexus

Answer 34

lesser occipital
great auricular
transverse cervical
supraclavicular nns
phrenic n.
Sensory fibers from C1 and C2 join the CN XII and follow it retrograde into the cranial vault where thy participate in innervating the dura mater of the posterior cranial fossa.

Question 35

Lesser occipital n.

Answer 35

(C2 and often C3) scalp above and behind the ear, upper portion of dorsum of ear

Question 36

Great auricular n.

Answer 36

C2 and C3

cutaneous innervatino over the superior portion of the SCM, angle of hte mandible and parotid region

Question 37

Transverse cervical n.

Answer 37

(C2 and C3)
skin over the anterior triangle of the neck; forms ansa cervicalis superficialis by ansotomosing with the cervical branch of the facial n. deep to the platysma

Question 38

Supraclavicular nns

Answer 38

C3 and C4

medial, intermediate adn lateral; skin at the base of the neck, anterior upper thorax, lateral and superior shoulder.

Question 39

Phrenic n. (sensory)

Answer 39

C3,4,5- sensory innervation to the pericardium, central portion of the INFERIOR surface of the diaphragm, superior surface of the liver and gallbladder.

Question 40

proprioceptive fibers of C2-C4

Answer 40

travel “disguised” within the spinal accessory n and leave it again as it passes through the SCM (C2 & C3) and the trapezius (C3 & C4)

Question 41

Ansa cervicalis

Answer 41

C1 and C2 provide fibers which travel with the hypoglossal n. (CN XII) which, in turn, send a SUPERIOR ROOT (descendens hypoglossi) which parallels the carotid sheath internally between teh artery and vein.
C2 and C3 provide fibers which form an inferior root (descendens cervicalis) which passes from behind the carotid sheath, wraps around the internal jugular vein and joins the superior root to form the ansa (loop) whcih is variable in its location and may be found at any level from the angle of the mandible to the superior border of the clavicle
From the ansa indivudal branches are distributed to the infrahyoid muscles

Question 42

motor fibers from C1

Answer 42

continue disguised within the hypoglossal nerve and diverge from it to innervate the geniohyoid and thyrohyoid muscles

Question 43

Direct muscular branches from C1-C4

Answer 43

are provided to pre-vertebral muscles (longus capitis, longus colli, middle scalene)

Question 44

Phrenic n. (motor)

Answer 44

C3,4,5

Each phrenic n. innervates its corresponding hemi-diaphragm.

Question 45

Clinical note: accessory phrenic nerves

Answer 45

often occur from other branches of C3,4,5 sometimes arising from supraclavicular nerves or from the nerve to subclavius. The most frequent one, however, arises somewhere along the course of hte C5 spinal nerve and courses lateral to the phrenic n. In surgical cases where the diaphragm needs to be paralyzed for weeks, i.e. diaphragmatic hernia repair, the phrenic n. is crushed between forceps. if an accessory phrenic n. is present, it must also be crushed to achieve complete paralysis.