L4: Posterior triangle

Question 1

Clinical applications of posterior triangle

Answer 1

1. JVP
2. Central vein catheterization
3. Penetrating trauma
4. Cervical lymphadenopathy

Question 2

Cervical fascia - superficial

Answer 2

Superficial fascia = skin and fatty layer deep to skin
Contained in superficial fascia is platysma muscle
- Thin sheet of skeletal muscle that originates from
superficial fascia of thorax and runs upwards to attach to
mandible and blend with lower facial muscles
- innervated by cervical branch facial n (CN VII)

Question 3

Cervical fascia - deep

Answer 3

1. Investing layer - surround neck (like stocking) and encloses peripheral muscles (trapezius, SCM, strap muscles)
2. Pretracheal layer - encloses thyroid, larynx/trachea and pharynx/oesophagus
3. Prevertebral layer - encompasses vertebral column and paravertebral muscles
4. Carotid sheath - surrounds int. carotid a, int. jugular v, vagus n. Formed by investing, prevertebral and pretracheal layers at different levels

Question 4

Clinical points about deep cervical fascia

Answer 4

1. As prevertebral layer crosses ant. part of vertebral body it divides in 2
2. Posterior to oesophagus/pharynx, pretracheal layer is called buccopharyngeal fascia and behind this is a potential space important in metastases of cancer etc

Question 5

Cervical spaces

Answer 5

1. Pretracheal space = between investing and pretracheal
   layers e.g. infection in thyroid, drains to here
   Extends inferiorly from pharynx/larynx down to anterior
   part of superior mediastinum
2. Retropharyngeal space = behind buccopharyngeal
   fascia (pretracheal) and anterior to prevertebral layer
   Extends inferiorly from base of skull to upper part of
   posterior mediastinum
3. Fascial space = within prevertebral layer between
   vertebral bodies posteriorly and prevertebral fascia
   anteriorly, limited laterally by transverse process
   Extends from base of skull to diaphragm

Question 6

Boundaries of posterior triangle

Answer 6

(Posterior to) posterior border of SCM, superior border of clavicle and anterior border of trapezius

It is region V in the neck

Question 7

Roof of the posterior triangle

Answer 7

Investing layer of deep fascia and includes anything from superficial to investing layer:
skin, superficial fascia, sometimes post part of platysma muscle, external jugular v (post. ext. jugular v runs within superficial fascia)

Question 8

Contents of posterior triangle - arteries

Answer 8

Two branches of thyrocervical trunk (from subclavian a) - transverse cervical a and supraclavicular a are in triangle
The 3rd part of subclavian a (with the trunks of brachial plexus) is very low in post triangle lying under prevertebral fascia

Question 9

Apex contents of posterior triangle

Answer 9

At apex, occipital artery and greater occipital nerve emerge and run upward on scalp.
Numerous lymph nodes found within posterior triangle including occipital nodes at apex

Question 10

Contents of posterior triangle - veins

Answer 10

External jugular v (formed by post auricular v and retromandibular v) passes vertically down the neck from behind angle of mandible over SCM . It pierces investing fascia in anterior corner of post triangle joining subclavian v (forms brachiocephalic v)

Question 11

Accessory nerve pathway

Answer 11

Embedded in investing fascia which forms roof of triangle
Path: exits cranial cavity via jugular foramen, runs with internal jugular v. (and internal carotid a. [not from jugular foramen]) together with IX and X cranial nerve, then shifts from anterior to posterior triangle.
Accessory nerve enters triangle halfway down posterior edge of sternocleidomastoid, runs downward over the floor of the triangle and exits the triangle by penetrating anterior edge of trapezius ≈5cm above clavicle, and runs in an obliquely posterior direction.

Question 12

Accessory nerve supply and damage

Answer 12

Innervates SCM and trapezius
Damage to accessory nerve –> loss of function of trapezius so cannot fully abduct arm
No surface markings, runs within 2cm above greater auricular n in a different plane

Question 13

Cervical plexus

Answer 13

Formed by anterior rami of cervical nerves (C1-4) in substance of muscles within prevertebral layer
Consists of muscular (deep) branches and cutaneous (superficial) branches)

Muscular:

1. Phrenic nerve
2. Supply to prevertebral and lateral vertebral muscles
3. Forms ansa cervicalis innervating infrahyoid muscles

Cutaneous:

1. Lesser occipital n
2. Greater auricular n
3. Suprascapular n
4. Transverse cervical n

Question 14

Erb’s point

Answer 14

Important surgical landmark
Cutaneous nerves from cervical plexus reach Erbs point at posterior border of SCM and divide to final destinations
in 95% of cases, accessory n runs within 2cm above Erbs point

Question 15

Brachial plexus

Answer 15

Formed from anterior rami of C5-8 and the roots of the plexus are between the anterior and middle scalene muscles
(e.g. place brachial plexus block)

Question 16

Floor of posterior triangle

Answer 16

Prevertebral fascia and muscles deep to it form floor: splenius capitis, levator scapulae, posterior scalene, middle scalene, anterior scalene

Question 17

Muscle content of posterior triangle

Answer 17

Omohyoid muscle is found low in medial part of triangle and disappears under SCM, then emerges in ant. triangle
Inferior belly in post triangle
(Superior belly in ant. triangle)

Question 18

Lymphatics

Answer 18

Superficial cervical nodes: from occipital and mastoid nodes

Deep cervical nodes: from parotid, submental, submandibular nodes

Question 19

Posterior triangle lymph biopsy

Answer 19

Accessory n at risk of iatrogenic injury due to long and superficial course in posterior triangle
Incidence of injury up to 8% in post triangle

May also damage superficial branch of transverse cervical a (if in middle of triangle) or cutaneous nerves

Question 20

Central vein catheterization (where and risks)

Answer 20

Central venous catheters inserted into subclavian v, internal jugular v or their junction

Risks:

• Pneumothorax or arterial puncture leading to haemorrhage or haemothorax
• External jugular v (some bleeding)
• Accessory nerve (variations)
• Bleeding in carotid sheath = pressure on vagus n and internal/common carotid (symptoms of vagus: pain, muscle cramps, difficulty swallowing

Question 21

Decreasing injury in CVC

Answer 21

Use US guidance
In post approach, patient place in trendelenburg position with contralateral rotation of head
Point where int jugular v crosses post border of SMC = key landmark