L5: Posterior triangle

Question 1

What are the boundaries of the posterior triangle:

Answer 1

Ant: Post border of sternocleidomastoid muscle
Post: Ant border of trapezius muscle
Base: Middle 1/3 of clavicle
Apex: Back of the skull on the superior nuchal line

Question 2

What is the uses of posterior triangle

Answer 2

1. Central venous catheterisation done for internal jugular or subclavian vein: Used for JVP monitoring, chemotherapeutic agents admin, recurrent long term venous access.
2. Cervical lymphadenopathy for cancer metastasis

Question 3

What is the Arrangement of fascial layers in the neck from out to in , ant to post

Answer 3

A) Superficial fascia: 
B) Deep cervical fascia 
1.  Investing layer 
2.Pre tracheal   
3. Carotid sheaths 
4. Prevertebral

Question 4

Describe the structures within the superficial fascia -possible innervations

Answer 4

1. Platysma: Thin sheet of skeletal muscle which originates from sup fascia of thorax, inserts on mandible to blend with lower face muscles. Innervated by CN7

2, Superficial veins

3. Nerves
   - Cutaneous branches of the cervical plexus exiting deep fascia

a) Greater auricular back up to ear
b) Lesser occipital: occip skull
c) Transverse cervical: front of neck sensation
d) Supraclavicular: 3 branches down to clavicle.

4. Fatty tissue

Question 5

Describe the structures within the investing fascia -possible innervations

Answer 5

The peripheral muscles around the neck including:

1. trapezius
2. sternocleidomastoid,
3. infra-hyoid (strap) muscles
4. Accessory nerve

Question 6

Describe the structures within the pre tracheal fascia - what is its other name

Answer 6

1. Trachea/Larynx
2. Thyroid gland
3. continuous w fascia round Esophagus/ pharynx

Posterior to pharynx, layer is referred to as Buccopharyngeal fascia

Question 7

Describe the structures within the carotid sheaths - and the contributions the sheath itself

Answer 7

1. Internal jugular vein
2. Internal carotid artery
3. Vagus nerve
   Contributions:
   Anteriorlateral: Investing
   Medial: Pre tracheal
   Posterior: Pre-vertebral

Question 8

Describe the structures within the pre vertebral fascia -possible innervations

Answer 8

1. Paravertebral muscles (vertebral column muscles)
   Ant, mid, post, scalene muscles + deep muscles of the back
2. Spinal vertebrae- attached to ant surface of transverse processes and bodies of vertebrae in C1-C7

((3. Third part of subclavian artery underneath low down in the post triangle))

Question 9

What are the 3 cervical/fascial spaces : What are the two layers that make them, and how deep do they go.

Answer 9

1. Pretracheal: Investing fascia covering post surface of infrahyoid muscle to pretracheal fascia anterior to trachea + thyroid.
   Goes from pharynx/larynx to ant part of sup mediastinum
2. Retropharyangeal: between buccopharyngeal (post to pharynx/esophagus) and anterior prevertebral fascia .
   Goes between base of skull to upper part of post mediastinum
3. Prevertebral space within prevertebral layer: between vertebral bodies posteriorly and prevertebral fascia anteriorly- limited laterally by the transverse proccesses of cervical vertebrae.
   Goes between base of skull-> post mediastinum-> diaphragm

Question 10

Why are the cervical/fascial spaces important which is most

Answer 10

They are potential spaces which can provide a conduit for the spread of infections from the neck to the mediastinum.

Third Prevertebral space: Prevertebral is most dangerous as while it can go to the diaphragm, it can extend to the coccyx and allow metastases to go travel within the whole length of the spinal cord

Question 11

How many regions of the neck are they and why, which one is the Posterior triangle

Answer 11

There are 7 relating to where the lymphatics drain.

Posterior triangle is region 5.

Question 12

What 7 muscles make the floor of the posterior triangle

Answer 12

Floor: Prevertebral fascia covering from sup to inf:

(1. Semispinalis capitis)
2. Splenius capitis
3. Levator scapulae
4. Posterior
5. Middle
6. Anterior scalene muscles

(Sitting on top of this is the inferior belly of the omohyoid muscle crossing to the upper medial corner.)

Question 13

What structures make the roof and what structures are in the roof of the posterior triangle

Answer 13

1. Make the roof: Investing layer of cervical fascia (+ skin and sup fascia) with the thickness variable due to fat and length of neck
2. IN:
   - External jugular vein (piercing deep to fascia at anterior corner) + Posterior ext. jugular vein

Accessory nerve

Question 14

What are the major nerve contents of the Posterior triangle

Answer 14

Coming out underneath the Sternocleidomastoid muscle:

1. Accessory nerve: innervating SCM + Trap. within the investing fascia going downward over floor until exiting at trap (5cm above clavicle)
2. Cutaneous branches of cervical plexus exiting deep fascia-> sup fascia.

a) Greater auricular back up to ear
b) Lesser occipital: occip skull
c) Transverse cervical: front of neck sensation
d) Supraclavicular: 3 branches down to clavicle.

3. Deep to the SCM, ontop of Mid scalene = Brachial plexus (before division)

Question 15

When is the accessory nerve damaged 80% of time, how should this be tested for and avoided

Answer 15

Can be damaged in removal of lymph nodes: usually in the upper half of the neck for cancer metastases.
This is Iatrogenic injury.

If damaged, patient cannot fully abduct the arm as last 1/3 = SCM + trap.

It can be avoided by referring lymph node biopsy to ENT or general surgeon who knows anatomy and can use US well as Accesory nerve has highly variable course- (entry, exit and branching)
and surface landmarks are not reliable.

Question 16

What are the major arterial contents of the Posterior triangle

Answer 16

1. Third part of the subclavian artery underneath prevertebral fascia that comes out of ant + mid scalene muscles. Crosses the base of the posterior triangle
2. Thyrocervical trunk (arising from 1st part of Subclavian)
   a)Transverse cervical artery
   b) suprascapular artery
   Both crossing laterally towards the back.

Question 17

Describe the general path of drainage of lymph nodes of the head and neck from the 5 starting at the base of the skull-what are those

Answer 17

1. Superficial lymph nodes drain from the face and scalp: 
Occipital, 
Mastoid, 
Pre-auricular/parotid, 
Submental and 
Submandibular nodes

2. Drain to superficial cervical lymph nodes: along the ext jugular vein on the superficial surface of SCM
3. Deep cervical nodes: along int jugular vein.

(however some of the superficial lymph nodes drain directly to the deep cervical )

Question 18

What area of drainage and arteries are the 5 superficial nodes associated with

Answer 18

1. Occipital: Occipital artery- drainage from posterior scalp and neck
2. Mastoid: Posterior auricular artery = posterolateral half of scalp drainage
3. Pre-auricular: superficial temporal and transverse facial arteries: ant auricle surface, anterolateral scalp, upper half of face, eyelids and cheeks.
4. Submandibular: Facial artery: forehead, gingivae, teeth, tongue
5. Submental: centre part of lower lip, chin, floor of mouth, tip of tongue and lower incisor teeth

Question 19

What structures run at the apex of the post triangle

Answer 19

Occipital artery and the greater occipital nerve emerge and run upward on to the scalp

Question 20

What are the 3 ways Central venous catheterization can be done in the posterior triangle and what is at risk of damage and how can this risk be diminished

Answer 20

Internal jugular vein
1. Posterior approach: Done by patient in trendleberg position. Where the vein crosses the post border of SCM is key landmark

2. Anterior approach (Newer) Going between two heads of SCM.

Brachiocephalic vein
3. Just behind the sternoclavicular joint - however in chinese population the right brachiocephalic forms lateral to the joint

Risks

• Apex of lung: pneumothorax
• Puncture of common carotid: haemorrhage, haemothorax
• Vagus nerve injuries
• risk increase with increased attempts

So need to use ultrasound + surface anatomy helps to maximise success as well as pressure monitoring to distinguish between artery and vein.