Posterior Neck Triangles and Suboccipital Triangle

Question 1

[18-minute video]: Dissection of the Posterior Triangle of the neck

Answer 1

🔪

Question 2

[13-minute video]: the Subclavian artery

Answer 2

🙂

Question 3

a) State the extents of the neck.
b) Skeleton of the neck consists of:

Answer 3

a) Superiorly: the base of cranium and the inferior border of mandible
Inferiorly: the level of the thoracic inlet, clavicle and scapula

b) cervical spine, hyoid bone, laryngeal cartilages, and the base of skull.

Question 4

Describe the fascial organisation of the neck.

Answer 4

(a) Superficial fascia; consists of a thin layer of loose areolar tissue and contains a thin sheet of muscle called platysma. It also contains cutaneous nerves, superficial veins, superficial lymph nodes and lymph vessels.
(b) Deep cervical fascia [fascia colli]; consists of three layers
(i) Investing layer; follow the rule of 2
~ encloses 2 muscles, trapezius and sternocleidomastoid
~ forms roof of 2 triangles; anterior and posterior triangle
~ splits to enclose 2 glands; submandibular and parotid
~ splits to enclose 2 spaces; suprasternal and supraclavicular
~ forms 2 fascial slings (pulleys) for inferior belly of omohyoid and intermediate tendon of digastric
(ii) pretracheal fascia; covers the front and sides of the trachea. It splits to enclose the thyroid gland forming its capsule. It allows free movement of the trachea during swallowing.
(iii) prevertebral fascia; lies in front of the prevertebral muscles. It covers the phrenic nerve and scalene muscles as well.

[Diagram: Fascial Organization of the Neck, transverse section]
[Diagram 2: Fascial Organization of the Neck]
[Diagram 3: Fascial Organization of the Neck]
[Diagram 4: Fascial Organization of the Neck]
[Diagram 5: Fascial Organization of the Neck]

Further notes:
Modifications of the pretracheal layer: The fascia at the back of the thyroid lobe is thickened to form a ligament (ligament of Berry) which gains attachment to the cricoid cartilage. The carotid sheath is said to be formed from fusion of prevertebral fascia and pretracheal fascia.

Question 5

Osteology of the Hyoid Bone
Click on Answer to view.

Answer 5

[Diagram 1] [Diagram 2]

Notes:
~ This is a U-shaped bone that forms part of the laryngeal skeleton. It is suspended from the tips of the styloid processes by stylohyoid muscles and ligaments.
~ It is derived from 2nd and 3rd pharyngeal arches; lesser horns and upper part of the body arise from the 2nd pharyngeal arch whereas the lower part of the body and the greater horns arise from the third pharyngeal arch.
~ Its primary role is for muscle attachment, but it also provides structural support for the larynx and pharynx.
~ It is a delicate bone that has vital medicolegal relevance. It is commonly broken during strangulation. [X-ray image: hyoid fracture]

Question 6

The platysma muscle is a broad sheet of muscle of varying prominence within the subcutaneous tissue of the neck. State its innervation and the effect of its contractions.

Answer 6

(a) Innervation: cervical branch of facial nerve
(b) Effect of its contractions:
✔ mandibular depression
✔ depresses the lower lip and corners of the mouth in expressions of horror or surprise
✔ it creates tense oblique ridges in the lateral skin
✔ diminished concavity between the lower jaw and lateral neck

Further notes:
~ Acting from above, the platysma produces vertical ridges in the skin of the neck releasing the pressure of skin over the underlying veins and thus helps in the venous return. It, therefore, serves to ease the pressure of tight collar.
~ Though the risorius appears to be a continuation of platysma, it has a different nerve supply, namely, the buccal branch of facial nerve.

Question 7

State the anatomical landmarks of the posterior neck triangle.

Answer 7

• occiput
• mastoid process
• atlas
• axis
• clavicle
• [Diagram: surface anatomy of the neck]

Question 8

Describe the attachments, and clinical significance of investing fascia of the neck.

Answer 8

Attachments:
1. Superiorly: External occipital protuberance, superior nuchal line, mastoid process, and lower border of mandible from behind forwards.
2. Inferiorly: spine of scapula, acromion process, upper aspect of clavicle, and jugular notch of manubrium sterni from behind forwards.
3. Anteriorly across the midline, it becomes continuous with its counter part of the other side. In the anterior midline it is attached to symphysis menti, hyoid bone jugular notch from above downwards.
4. Posteriorly: Ligamentum nuchae and spine of 7th cervical vertebra.
5. [Diagram: investing fascia]

Clinical significance:
The investing fascia compartmentalizes neck structures, limiting the spread of infection (e.g., preventing a superficial skin abscess from spreading deeper into the neck).

Question 9

Above the suprasternal notch, the investing fascia of the neck splits into two layers to enclose suprasternal space (of Burns) before being attached to the anterior and posterior borders of the suprasternal notch. State the contents of the suprasternal notch.

Answer 9

(a) sternal heads of sternocleidomastoid muscles,
(b) jugular venous arch,
(c) interclavicular ligament, and
(d) lymph node (sometimes).

[Diagram: Sternum]
[Diagram: Suprasternal space]
[Diagram 1: Contents of the Suprasternal space]
[Diagram 2: Contents of the Suprasternal space]
[Diagram illustrating the splitting of the investing fascia to enclose the suprasternal notch]

Question 10

Above the middle third of clavicle, the investing fascia splits into two layers to enclose the supraclavicular space. The anterior and posterior layers get attached to the anterior and posterior borders of the upper surface of the clavicle. The posterior layer encloses the inferior belly of omohyoid and after being attached to clavicle it becomes continuous with the posterior layer of clavipectoral fascia. State the contents of the supraclavicular space.

Answer 10

(a) terminal part of the external jugular vein, and
(b) supraclavicular nerves before they become cutaneous.

[Diagram: Supraclavicular Space]

Question 11

State the boundaries of the posterior neck triangle.

Answer 11

Anterior border: Posterior border of sternocleidomastoid muscle
Posterior border: Anterior border of trapezius muscle
Inferior border: middle 1/3 of clavicle
Superior border (apex): Meeting point of sternocleidomastoid and trapezius muscles at the superior nuchal line of the occipital bone.
[Diagram]

Note: The sternocleidomastoid muscle runs diagonally across the neck and divides it into anterior and posterior triangles.

Question 12

State the following regarding the sternocleidomastoid muscle: attachments, actions, blood supply, and nerve supply.

Answer 12

Origin:
Arises by 2 heads: [Diagram]
1. Sternal head: arises by a rounded tendon from the superolateral part of the front of the manubrium sterni
2. Clavicular head, is flat and musculoaponeurotic. It arises from the medial third of the superior surface of the clavicle
Insertion: by (a) a thick tendon on the lateral surface of the mastoid process extending from its tip to its base, and (b) by a thin aponeurosis into the lateral half of the superior nuchal line of the occipital bone.
Arterial Supply:
The sternocleidomastoid is supplied by branches of following arteries:
1. Upper part, by occipital and posterior auricular arteries
2. Middle part, by superior thyroid artery
3. Lower part, by suprascapular artery
Innervation:
~ Spinal accessory nerve.
~ Ventral rami of C3 and C4, which are mostly sensory and carry proprioceptive sensations from the muscle.
Actions:
Unilateral contraction:
1. ipsilateral neck flexion
2. contralateral rotation of the head
Bilateral contraction:
1. flexion of lower and middle cervical spine
2. extension of atlanto-occipital joint

Question 13

State the relations of the sternocleidomastoid muscle.

Answer 13

[This is best studied with an atlas!]

Superficial Relations
✔ Skin
✔ Platysma
✔ Cutaneous nerves: (a) Great auricular, (b) Transverse cervical, (c) Medial supraclavicular, (d) Lesser occipital
✔ External jugular vein
✔ Superficial cervical lymph nodes
✔ Parotid gland

Deep Relations
In the upper part
(a) Muscle: Posterior belly of digastric, longissimus capitis, and splenius capitis
(b) Artery: Occipital artery
In the middle part
(a) Muscles: Levator scapulae, scalenus anterior, scalenus medius, scalenus posterior, splenius capitis, inferior belly of omohyoid
(b) Arteries: Common carotid, internal carotid
(c) Veins: Internal jugular, anterior jugular
(d) Nerves: Vagus, spinal accessory, cervical plexus, brachial plexus (upper part), ansa cervicalis (inferior root)
(e) Glands: Thyroid gland, lymph nodes
In the lower part
(a) Muscles: Sternohyoid, sternothyroid, scalenus anterior
(b) Arteries: Suprascapular, transverse cervical
(c) Veins: Anterior jugular
(d) Nerves: Brachial plexus (lower part), phrenic nerve

Question 14

State the clinical relevance of the sternocleidomastoid muscle.

Answer 14

☯︎ Torticollis or wry neck: It is a clinical condition in which head is bent to one side and chin points to the opposite side. This occurs due to spasm of sternocleidomastoid and trapezius muscles supplied by spinal accessory nerve.
– The spasmodic torticollis is characterized by repeated painful contractions of the trapezius and sternocleidomastoid muscles on one side. It is usually caused by exposure to cold and maladjustment of pillow during sleep.
– The reflex torticollis occurs due to irritation of spinal accessory nerve caused by inflamed or suppurating lymph nodes.
– The congenital torticollis occurs due to birth injury to muscle. Permanent torticollis may occur due to subsequent ischemic contracture.
☯︎ Sternomastoid tumor: It is the swelling in the middle third of the sternocleidomastoid muscle due to edema and ischemic necrosis caused by birth trauma.

Question 15

Outline the structures present in the superficial fascia of the posterior neck triangle.

Answer 15

☑ platysma
☑ 4 cutaneous branches of the cervical nerve plexus: lesser occipital, great auricular, transverse cutaneous nerve of neck, supraclavicular nerves (lateral, intermediate and medial)
☑ external jugular vein [formed behind the angle of the mandible by joining of the posterior division of the retromandibular vein and the posterior auricular vein. It drains into the subclavian vein.]

Question 16

a) What forms the roof of the posterior neck triangle?
b) What structures pierce the roof of the posterior triangle?

Answer 16

a) It is formed by the investing layer of the deep cervical fascia, stretching between the sternocleidomastoid and trapezius muscles.
b) Structures that pierce its roof:
1. Four cutaneous branches of cervical plexus:
✔ Lesser occipital nerve (C2)
✔ Great auricular nerve (C2, C3)
✔ Transverse cervical nerve (C2, C3)
✔ Supraclavicular nerves (C3, C4).
They pierce the roof near the middle of the posterior border of the sternocleidomastoid muscle.
2. External jugular vein: It begins just below the angle of mandible, runs downwards and backwards crossing the sternocleidomastoid obliquely and under the cover of platysma.

Question 17

(a) What forms the floor of the posterior neck triangle?
(b) The muscular floor of posterior triangle is covered by prevertebral layer of deep cervical fascia, which forms the ________________ of the floor of the posterior triangle.

Answer 17

(a) The floor of posterior triangle is muscular and is formed from above downwards by the following muscles:
1. Semispinalis capitis
2. Splenius capitis
3. Levator scapulae
4. Scalenus medius
5. First digitation of serratus anterior (sometimes).
[Diagram: Floor of the Posterior Triangle of Neck]
(b) fascial carpet

Further notes:
☑ The fascial carpet forms axillary sheath around subclavian artery and brachial plexus travelling from the root of the neck to the upper limb.
☑ The lower part of the posterior triangle is crossed by inferior belly of omohyoid superficial to the fascial carpet.

Question 18

Semispinalis capitis
(a) Origin
(b) Insertion
(c) Action
(d) Innervation

Answer 18

(a) Origin: articular processes of vertebrae C4-C7, transverse processes of vertebrae T1-T6
(b) Insertion: Between superior and inferior nuchal lines of occipital bone
(c) Action: Bilateral contraction - extension of head, cervical and thoracic spine Unilateral contraction - lateral flexion of head, cervical and thoracic spine (ipsilateral), rotation of head, cervical and thoracic spine (contralateral)
(d) Innervation: descending branches of greater occipital nerve (C2) and spinal nerve C3

Question 19

State the clinical correlation regarding the fascial carpet of the posterior triangle of the neck.

Answer 19

Pus collected in the posterior triangle deep to its fascial carpet from tubercular cervical vertebrae [tuberculosis infection] may track downwards and laterally along the axillary sheath to first appear in the axilla or even in the arm subsequently. [The prevertebral fascia extends around the brachial plexus and axillary artery (continuation of subclavian artery) as the axillary sheath.]

Question 20

The posterior triangle is subdivided into two parts by the inferior belly of the omohyoid, which crosses the lower part of the triangle obliquely upwards and forwards. List those two parts.

Answer 20

(a) a larger upper part called occipital triangle
(b) a small lower part called subclavian (supraclavicular) triangle.
[These parts are so named because they contain occipital and subclavian arteries, respectively.]

[Diagram]

Question 21

State the contents of the occipital triangle.

Answer 21

(a) Spinal accessory nerve
(b) 3rd and 4th cervical nerves providing branches to levator scapulae and trapezius muscles
(c) Dorsal scapular nerve (C5)
(d) Four cutaneous branches of cervical plexus (initial parts)
(e) Occipital artery
[Diagram: Contents of the Posterior Triangle of the Neck]

Further notes:
~ The spinal accessory nerve comprises the true content(s) of the posterior triangle and all others are behind or front of the fascial floor.
~ The most important contents of posterior triangle are: (a) third part of subclavian artery, (b) brachial plexus (cervical part), (c) spinal accessory nerve, and (d) lymph nodes.
~ All the important contents of the posterior triangle lie deep to the fascial carpet of the floor except spinal accessory nerve, which lies just underneath the roof. In operations on the posterior triangle all the structures except spinal accessory nerve are safe, provided fascial carpet of posterior triangle is left intact. The spinal accessory nerve can be injured in surgery requiring the removal or biopsy of lymph nodes in the posterior triangle of the neck.

Question 22

State the contents of the subclavian/supraclavicular triangle.

Answer 22

(a) 3rd part of the subclavian artery
(b) Subclavian vein
(c) Terminal part of external jugular vein
(d) Trunks of brachial plexus
(e) Superficial transverse cervical, suprascapular, and dorsal scapular arteries
(f) Lymph nodes
[Diagram: Contents of the Posterior Triangle of the Neck]

Further notes:
~ The spinal accessory nerve comprises the true content(s) of the posterior triangle and all others are behind or front of the fascial floor.
~ The most important contents of posterior triangle are: (a) third part of subclavian artery, (b) brachial plexus (cervical part), (c) spinal accessory nerve, and (d) lymph nodes.
~ All the important contents of the posterior triangle lie deep to the fascial carpet of the floor except spinal accessory nerve, which lies just underneath the roof. In operations on the posterior triangle all the structures except spinal accessory nerve are safe, provided fascial carpet of posterior triangle is left intact. The spinal accessory nerve can be injured in surgery requiring the removal or biopsy of lymph nodes in the posterior triangle of the neck.

Question 23

The roots of the brachial plexus are situated between which two muscles?

Answer 23

scalenus anterior [anteriorly] and scalenus medius [posteriorly]
[Diagram illustrating this]
[Cadaveric image: Brachial plexus roots and trunks]

Question 24

Name the lymph nodes of the posterior triangle of the neck.

Answer 24

1. occipital lymph nodes
2. lymph nodes along the spinal accessory nerve
3. supraclavicular lymph nodes

Question 25

What is the clinical relevance of the left supraclavicular lymph nodes (aka. Virchow’s nodes)?

Answer 25

These lymph nodes may get enlarged in cancer of the stomach, colon, testis, lung and mammary gland. The biopsy of these lymph nodes is helpful in early diagnosis of distant malignancies.

Question 26

The accessory nerve is a content of the occipital triangle. Its approximate course is marked by a line connecting two points. State those two points.

Answer 26

• a point slightly superior to the middle of the posterior border of the sternocleidomastoid.
• a point about 5 cm superior to the clavicle at the anterior border of the trapezius.
• [Diagram: Accessory nerve]

Question 27

State the course of the spinal accessory nerve.

Answer 27

• enters cranial cavity via the foramen magnum to join the cranial accessory nerve
• exits the cranial cavity via the jugular foramen
• enters the deep surface of the sternocleidomastoid muscle (on its proximal part)
• crosses the posterior triangle (on levator scapulae) to reach the trapezius muscle [PRO-TIP: This particular part of its course will help you identify accessory nerve on a cadaver.]
• [Diagram: Accessory nerve]

Question 28

a) State the clinical correlation regarding relation of lymph nodes to the spinal accessory nerve.
b) State the effects of lesion on the spinal accessory nerve.

Answer 28

a) The spinal accessory nerve may be damaged in operations involving the removal or biopsy of lymph nodes in the posterior triangle of the neck.
b) ~ Paralysis of trapezius if the nerve is injured in the posterior triangle
~ Supranuclear lesions have ipsilateral paralysis of trapezius muscle (reason: double decussation of the spinal accessory nerve), but contralateral paralysis of SCM muscle

Question 29

Cervical plexus
a) Site
b) Formation
c) Branches
d) Clinical anatomy

Answer 29

a) Site
✔ in front of the scalenus medius
✔ deep to the prevertebral fascia
b) Formation
✔ by ventral rami of C1-C4
✔ each ramus (except C1) divides into ascending and descending parts and unite in communicating loops
c) Branches
Cutaneous branches:
✔ lesser occipital
✔ greater auricular
✔ transverse cervical
✔ supraclavicular
Muscular branches:
✔ to sternocleidomastoid (ventral rami of C3, C4)
✔ to trapezius and levator scapulae (ventral rami of C3, C4)
✔ to scalene muscles
✔ ansa cervicalis to infrahyoid muscles
✔ Phrenic nerve (an anterior relation of scalenus anterior): supplies the diaphragm
d) Clinical anatomy
✔ administration of cervical nerve block: targets the superficial branches as they emerge (together) at the posterior border of sternocleidomastoid

[Diagram: Cervical Plexus]

Question 30

Although the cervical plexus is located deep to the sternocleidomastoid, its cutaneous branches emerge at the midpoint or just above the midpoint of the posterior border of the sternocleidomastoid by piercing the deep cervical fascia. Describe the course and distribution of the lesser occipital and great auricular nerves [more emphasis on distribution].

Answer 30

1. Lesser occipital nerve
   Course: hooks around the spinal accessory nerve and ascends for a short distance along the posterior border of sternocleidomastoid
   Distribution: skin of the upper one-third of the cranial surface of the auricle and that of the head behind the auricle.
2. Great auricular nerve
   Course: runsforwardsandupwards across the sternocleidomastoid towards the angle of mandible where it divides into anterior and posterior branches.
   Distribution: first supplies the skin of the face over the angle of the mandible and then the skin over the mastoid region and lower part of both the surfaces of the auricle.
3. [Diagram: 4 cutaneous branches of the cervical plexus]
4. [Diagram: cervical plexus]

Question 31

Although the cervical plexus is located deep to the sternocleidomastoid, its cutaneous branches emerge at the midpoint or just above the midpoint of the posterior border of the sternocleidomastoid by piercing the deep cervical fascia. Describe the course and distribution of the transverse cervical nerve/anterior cutaneous nerve of the neck and the supraclavicular nerves [more emphasis on distribution].

Answer 31

1. Transverse cervical nerve/anterior cutaneous nerve of the neck
   Course: passes forward across the sternocleidomastoid deep to the external jugular vein and then divides into ascending and descending branches.
   Distribution: supplies the skin of the front of the neck.
2. Supraclavicular nerves
   Course: rises as a common trunk which descends downwards and divides into medial, intermediate, and lateral supraclavicular nerves.
   Distribution: (i) The medial supraclavicular nerve crosses in front of the medial one-third of the clavicle to supply the skin on the chest up to the 2nd rib.
   (ii) The intermediate supraclavicular nerve passes in front of the middle third of the clavicle to supply the skin on the front of the chest. Occasionally it pierces the clavicle through and through.
   (iii) The lateral supraclavicular nerve crosses in front of the lateral third of the clavicle and sup- plies the skin over the shoulder and the upper half of the deltoid muscle.
3. [Diagram: 4 cutaneous branches of the cervical plexus]
4. [Diagram: cervical plexus]

Question 32

What is nerve point of the neck, and its clinical significance?

Answer 32

The point at the junction of the upper and middle third of the posterior border of sternocleidomastoid where four cutaneous nerves and spinal accessory nerve emerge is termed nerve point of the neck.
Clinical significance: In cervical plexus nerve block the anaesthetic agent is injected at the nerve point.

[Diagram: nerve point of the neck]

Question 33

State the root values of:
1. Lesser occipital nerve
2. Greater auricular nerve
3. Transverse cervical nerve
4. Supraclavicular nerve

Answer 33

1. C2
2. C2, C3
3. C2, C3
4. C3, C4

Question 34

a) List the nerves that arise directly from the roots of the brachial plexus, stating the muscles that they supply.
b) List the nerves that arise from trunks of the brachial plexus, stating the muscles that they supply. Do all trunks have nerves arising from them?

Answer 34

a) nerves arising from the roots
✔ dorsal scapular nerve (C5): rhomboids and levator scapulae
✔ long thoracic nerve (C5, C6, C7): serratus anterior
b) Only 2 nerves arise from the upper trunk. No other nerves arise from the other trunks. These 2 nerves are:
✔ suprascapular nerve: supraspinatus, infraspinatus
✔ nerve to subclavius: subclavius
They arise from Erb’s point.

Question 35

State the origin, course and termination of the subclavian artery.

Answer 35

ORIGIN:
1. The right subclavian artery arises from the brachiocephalic trunk behind the right sternoclavicular joint at the root of neck.
2. The left subclavian artery arises from the arch of aorta in the thorax. It runs upwards on the left mediastinal pleura and makes groove on the left lung and enters the neck by passing behind the left sternoclavicular joint.
COURSE:
In the neck, both the arteries pursue a similar course.
On each side, the subclavian artery arches laterally across the anterior surface of the cervical pleura onto the first rib posterior to the scalenus anterior muscle.
TERMINATION:
At the outer border of first rib where the subclavian artery continues as the axillary artery.

[Diagram: subclavian artery origin]

Further notes:
Note that the subclavian artery is so called because it is located beneath the clavicle. It is the main source of blood supply to the upper limb and hence called artery of the upper limb. However, the subclavian artery also supplies considerable part of the thoracic wall, head, neck, and brain through its branches.

Question 36

State the parts of the subclavian artery. What divides it into three parts?

Answer 36

The scalenus anterior muscle divides it into three parts:
1. First part—extends from origin to medial border of scalenus anterior.
2. Second part—lies behind the scalenus anterior muscle.
3. Third part—extends from the lateral border of scalenus anterior to the outer border of the first rib.

Question 37

State the branches of the subclavian artery.

Answer 37

The subclavian artery usually gives off four branches. All of them arise from first part with the exception of costocervical trunk, which on the right side arises from the second part.

From the first part:
1. Vertebral artery
2. Thyrocervical trunk:
– Inferior thyroid artery
– Transverse cervical artery
– Suprascapular artery
3. Internal thoracic artery
4. Costocervical trunk (on left side only)

From the second part:
Costocervical trunk (on right side only)

From the third part:
Dorsal scapula artery: It is an occasional branch that may arise from the third part of the subclavian artery. When present, it replaces the deep branch of the transverse cervical artery.

[Diagram: Branches of the Subclavian Artery]

Question 38

State the clinical relevance of the subclavian artery.

Answer 38

Subclavian steal syndrome: If there is obstruction of the subclavian artery proximal to the origin of vertebral artery, some amount of blood from opposite vertebral artery will pass in a retrograde fashion to the subclavian artery of the affected side through the vertebral artery of that side to provide the collateral circulation to the upper limb on the side of lesion. Thus there occurs a sort of stealing of blood of brain by the subclavian artery of the affected side. Hence, the name subclavian steal syndrome.
[Diagram: Illustration of Subclavian Steal Syndrome]

Question 39

State the following regarding anterior scalene/scalenus anterior muscle: attachments, innervation, actions and clinical significance.

Answer 39

Origin: From anterior tubercles of transverse processes of C3, C4, C5, and C6 vertebrae (i.e., all typical vertebrae).
Insertion: Scalene tubercle on the inner border of the 1st rib and to the ridge on the upper surface of the rib anterior to the groove for the subclavian artery.
Innervation: By ventral rami of C4, C5, and C6 spinal nerves.
Actions:
1. Unilateral contraction of the anterior scalene causes ipsilateral contraction of the neck (lateral flexion).
2. Bilateral contraction of the anterior scalene causes flexion of the neck.
Clinical significance:
~ landmark for identifying the parts of the subclavian artery
~ Thoracic outlet syndrome: The anterior scalene muscle can be involved in certain forms of thoracic outlet syndrome. This condition may cause symptoms that mimic a spinal disc herniation of the cervical vertebrae.
~ Myofascial pain syndrome: The anterior scalene muscle can contribute to myofascial pain syndrome. Symptoms associated with this syndrome can resemble those of a cervical disc herniation.

The anterior scalene: [Diagram 1] [Diagram 2] [Cadaveric image]
Osteology of the first rib: [Diagram 3] [Diagram 4]

Further notes:
~ Scalenus anterior is supplied by the ascending cervical branch of the inferior thyroid artery.
~ Anatomical variation of ascending cervical artery? In some people, it arises from the thyrocervical trunk.

Question 40

inter-scalene (aka. scalene) triangle
(a) boundaries
(b) contents
(c) clinical relevance

Answer 40

(a) boundaries
✔ anteriorly: scalenus anterior
✔ posteriorly: scalenus medius
✔ base (inferiorly): first rib

(b) contents
✔ roots and trunks of the brachial plexus
✔ 2nd part of the subclavian artery

(c) clinical relevance
Interscalene block: This is a regional anaesthesia technique that involves injecting local anaesthetic around the brachial plexus roots and trunks within the interscalene triangle. This block is commonly used for shoulder and limb surgery to provide effective anaesthesia.

[Diagram: Inter-scalene triangle]

Question 41

Discuss the scalene syndrome.

Answer 41

It consists of group of signs and symptoms produced due to compression of lower trunk of brachial plexus (C8 and T1) and subclavian artery in the scalene triangle either due to raising of its base by the cervical rib, if present, or due to spasm of scalene muscles. Clinically, this syndrome presents as:
(a) tingling sensation and numbness along the inner border of forearm and hand, i.e., along the distribution of C8 and T1 spinal nerves,
(b) progressive paresis [weakness/partial paralysis] and wasting of intrinsic muscles of the hand (most of them are supplied by C8 and T1 spinal nerves), and
(c) ischemic pain and absence of radial pulse due to compression of subclavian artery.

Question 42

State the formation, course, termination, and surface anatomy of the external jugular vein.

Answer 42

Formation: Begins just below the angle of the mandible by the union of posterior division of retromandibular vein and posterior auricular vein.
Course and Termination: It then runs almost vertically downward across the sternocleidomastoid under the cover of platysma to pierce the deep cervical fascia in the anteroinferior angle of the posterior triangle about 2.5 cm above the clavicle along the posterior border of the sternocleidomastoid and enters the supraclavicular space. After passing through this space it terminates in the subclavian vein.
Surface Anatomy: The external jugular vein can be marked on the surface by a line extending downward and backward from angle of the mandible to the middle of the clavicle.

[Diagram: External Jugular Vein and its Tributaries]

Question 43

State the tributaries of the external jugular vein.

Answer 43

Formative tributaries:
1. Posterior auricular vein
2. Retromandibular vein

Tributaries that are neither formative nor terminal:
3. Posterior external jugular vein
4. Oblique jugular vein

Terminal tributaries:
5. Transverse cervical vein
6. Suprascapular vein
7. Anterior jugular vein

[Diagram]: External Jugular Vein and its Tributaries

Must know:
✓ The posterior auricular vein descends behind the auricle to join the posterior division of retromandibular vein.
✓ Posterior external jugular vein descends along the posterior border of sternocleidomastoid to join the external jugular vein a little below the midpoint of posterior border of the muscle.
✓ The oblique jugular vein communicates with the internal jugular vein in the upper part of the neck.
✓ The suprascapular, transverse cervical, and anterior jugular veins join the external jugular vein in the posterior triangle.

There are two pairs of valves in the lumen of the external jugular vein, one at its site of termination into the subclavian vein and the other about 4 cm above the clavicle. These valves, however, do not prevent regurgitation of blood.

Question 44

State the tributaries of the internal jugular vein.

Answer 44

☛ inferior petrosal sinus [may or may not be a tributary depending on how you understand the formation of the internal jugular vein]
☛ pharyngeal veins [from the pharyngeal plexus]
☛ common facial vein [formed by union of the anterior division of the retromandibular vein and the facial vein]
☛ lingual vein
☛ superior thryoid vein
☛ middle thyroid vein
☛ occipital vein [sometimes]

Question 45

Discuss venous air embolism with regard to external jugular vein.

Answer 45

The wall of the external jugular vein is adherent to deep fascia where it pierces the deep fascia (about 2.5 cm above the clavicle). Therefore, if external jugular vein is cut at this site, its walls cannot collapse. Consequently, air is sucked into its lumen due to negative intrathoracic pressure during inspiration leading to venous air embolism which may cause death subsequently.

Question 46

Discuss central venous cannulation with regard to external jugular vein.

Answer 46

The external jugular vein is occasionally used for central venous cannulation, but due to its variable size and presence of valves it is often difficult to manipulate the cannula through the lower part of the vein. The right external jugular vein being in the most direct line with the superior vena cava, is the one most commonly used.

Question 47

Discuss assessment of venous pressure with regard to external jugular vein.

Answer 47

The external jugular vein is often examined by clinicians to assess the venous pressure in the right atrium. Normally, in recumbent (lying down) position, the lower one-third of the vein becomes filled with blood but it collapses on reclining at 45° angle. However, if it remains full even when the patient reclines at 45° angle, it suggests increased right atrial pressure often seen in congestive cardiac failure.

Question 48

State the origin, course and termination of anterior jugular vein.

Answer 48

Origin: Arises near the hyoid bone from the confluence of the superficial submental veins.
Course:
- descends between the midline and anterior border of sternocleidomastoid
- they unite above the manubrium of the sternum by the jugular venous arch
Termination: Into either the external jugular vein or subclavian vein
[Diagram]

Question 49

subclavian veins
(a) tributaries
(b) clinical relevance

Answer 49

(a) tributaries
✔ internal jugular vein
✔ external jugular vein
✔ dorsal scapular vein
✔ anterior jugular vein

(b) Clinical relevance: The subclavian vein is a common site of central venous catheterization.

Further notes:
Central venous catheterization: Central venous catheterization, also known as a central line or central venous access catheter, involves inserting a catheter into one of the large veins in the neck, upper chest, or groin. This may be for delivery of medications or fluids, prolonged venous treatments or specialized treatments such as hemodialysis, plasmapheresis, invasive hemodynamic monitoring etc.
Catheter: is a general term for a tube inserted into the body for various purposes.

Question 50

The omohyoid muscle consists of 2 bellies, superior and inferior belly united at an angle by an intermediate tendon. State its origin, insertion, innervation and action.

Answer 50

Origin: upper border of the scapula, near the notch
Insertion: lower border of hyoid body
Innervation: the ansa cervicalis
Action: depresses hyoid bone

Question 51

branches from the costocervical trunk of the subclavian artery

Answer 51

1. Deep cervical artery: supplies deep structures in the neck
2. Supreme/superior intercostal artery: supplies upper part of intercostal spaces especially posteriorly
3. [Diagram]

Question 52

suboccipital triangle
(a) boundaries
(b) contents
(c) clinical importance

Answer 52

(a) boundaries
✔ anteriorly: posterior arch of the atlas and the posterior atlanto-occipital membrane (ligament)
✔ posteriorly (roof): semispinalis capitis muscle
✔ superomedial border: rectus capitis posterior major muscle
✔ superolateral border: obliquus capitis superior muscle
✔ inferolateral border: obliquus capitis inferior muscle

(b) contents
✔ third part of the vertebral artery
✔ suboccipital nerve aka. dorsal ramus of C1
✔ suboccipital venous plexus

(c) clinical relevance
Occipital neuralgia: Irritation or compression of the suboccipital nerve can lead to occipital neuralgia, characterized by severe headaches radiating from the base of the skull to the back of the head.
Vascular access: Surgeons and anesthesiologists use the suboccipital triangle for vascular access during certain procedures.

[Diagram: Sub-occipital triangle]

Question 53

suboccipital venous plexus
(a) communications
(b) clinical relevance

Answer 53

(a) communications
✔ External Vertebral Venous Plexuses: These veins travel inferiorly from the suboccipital region to drain into the brachiocephalic vein.
✔ Occipital Vein: The occipital vein joins the suboccipital venous plexus deep to the musculature of the back.
✔ [Diagram 1] [Diagram 2]

(b) clinical relevance
✔ When jugular circulation is compromised, the suboccipital venous plexus can provide an alternative route for venous drainage.

Question 54

Outline the course of the subclavian veins.

Answer 54

✔ The subclavian veins are the continuation of the axillary veins.
✔ It extends from the outer border of the 1st rib to the medial border of scalenus anterior.
✔ It joins the internal jugular vein to form the brachiocephalic vein.
✔ It receives the external jugular vein, dorsal scapular vein and anterior jugular vein.
✔ The thoracic duct enters at the junction between the left subclavian vein and the internal jugular vein.
✔ The right lymphatic duct enters at the junction between the right subclavian vein and the internal jugular vein.

Further notes:
~ The subclavian vein is a common site of central venous catheterization.
~ The function of the thoracic duct is to transport lymph back into the circulatory system.

Question 55

The cutaneous nerves of the neck are derived from both dorsal and ventral rami of cervical spinal nerves. List the branches from the:
(a) ventral rami
(b) dorsal rami

Answer 55

(a) lesser occipital, great auricular, transverse cutaneous and supraclavicular nerves
[Note: these arise from the cervical plexus (C2-4) and supply the skin of the mandibular angle, anterior neck and lateral neck]

(b) greater occipital nerve (C2), and the dorsal rami of C3, C4 and C6 which pierce trapezius muscle.
[Note that these arise from C2-C6 rami and supply skin over the back of the neck and scalp.]

Question 56

Name the structures surrounded by the carotid sheath.

Answer 56

✔ common and internal carotid arteries
✔ internal jugular vein
✔ vagus nerve
✔ deep cervical lymph nodes
✔ [Diagram]