L18: applied anatomy of the larynx

Question 1

Describe the management for epistaxis

Answer 1

Simple first aid measures – stops most nose bleeds
If fails – attempt simple cautery/topical vasoconstrictors
If fails – anterior packing (nasal tampons)
If fails – posterior packing +/- surgical intervention (eg. SPA ligation)

Question 2

List the functions of larynx

Answer 2

1) Airway protection – preventing food/fluid etc entering airways
2) Ventilation – for movement of air into/out of lungs
3) Key role in cough reflex – rapidly expel anything inadvertently entering airway
4) Role in phonation of sound

Question 3

Describe the anatomy of the larynx

Answer 3

‘Tube’ created by ligaments, membranes, cartilages & muscles
Suspended from and lies below the hyoid bone
Part of the upper respiratory tract
Begins at the laryngeal inlet & ends at lower border of cricoid cartilage (C6)
Continues as the trachea

Question 4

List the cartilages which help form the structural framework of the larynx

Answer 4

Epiglottis
Thyroid cartilage
Cricoid cartilage
Arytenoid cartilage

Question 5

Describe the structural framework of the larynx (membranes and ligaments)

Answer 5

Thyroid cartilage is attached superiorly to the hyoid bone by the thyrohyoid cartilage
Cricothyroid membrane runs upwards from the cricoid cartilage -> thyroid cartilage (deep to this, giving a free upper margin)
Free upper margin attaches anteriorly to the inner surface of thyroid cartilage & posteriorly to arytenoid cartilages
Upper margin is thickened = vocal ligament -> gives shape and structure to the true vocal cord

Question 6

Describe cricothyroidotomy

Answer 6

In acute laryngeal obstruction, cricothyroid membrane is punctured
Allows rapid access into the infraglottic area of the larynx
Provides a temporary solution until a more definitive airway can be established
Rare, but may be required in situations of ‘can’t intubate, can’t ventilate’

Question 7

Describe the attachments of the epiglottis

Answer 7

Attachment to the hyoid & back of the thyroid cartilage
Sides of the epiglottis are connected to the arytenoids by aryepiglottic folds -> quadrangular membrane joins the sides of the epiglottis to the arytenoids, giving shape to these folds
This forms the margins of the entrance, or aditus, of the larynx

Question 8

Describe the anatomy of the thyroid & cricoid cartilage

Answer 8

Thyroid cartilage – made up of two lateral plates meeting in the midline as a prominent ‘V’ = laryngeal prominence
Cricoid cartilage is the only complete ring of cartilage throughout the respiratory tract
Inferiorly, attached to the trachea by the cricotracheal membrane; arytenoids sit on top of the cricoid cartilages posteriorly, one on each side

Question 9

Describe what creates the false and true vocal cord

Answer 9

False – free lower border of quadrangular membrane = vestibular ligament
True – free upper border of cricothyroid membrane = vocal ligament
-space in the middle between the true vocal cords is the rima glottidis

Question 10

Describe the three divisions the larynx is divided into internally

Answer 10

1) Supraglottis – epiglottis up to & including the false cords
2) Glottis – below false cords, includes the true cords until ~1cm below
3) Infraglottis – below true VCs to inferior boundary of cricoid

Question 11

Which epithelium lines the larynx?

Answer 11

Pseudostratified ciliated columnar epithelium

EXCEPT: the true vocal cords are lined with stratified squamous

Question 12

Describe intubation (laryngoscopic view)

Answer 12

Anaesthetist will view the larynx using a laryngoscope
Process of intubation requires an ET tube, passed through the patient’s oral cavity, oropharynx, larynx, vocal cords – sits in the upper part of the trachea
ET tube has a small balloon at the end that is inflated -> tube remains in place (has a lumen which allows for mechanical ventilation and oxygenation of the patient’s lungs)

Question 13

Describe the two main actions of the intrinsic laryngeal muscles

Answer 13

1) Alter size and shape of laryngeal inlet
- muscles within aryepiglottic folds can contract, narrow laryngeal inlet & flatten position of epiglottis
- protect larynx during swallowing
2) Alter tension in and position of true vocal cords
- muscles within larynx alter position of arytenoid cartilages (vary position of cords)
- protects larynx during swallowing and enables phonation

Question 14

What nerve are the intrinsic laryngeal muscles supplied by?

Answer 14

Recurrent laryngeal nerve of vagus
Right half = right recurrent laryngeal nerve
Left half = left recurrent laryngeal nerve
EXCEPT: cricothyroid muscle – external branch of superior laryngeal nerve of vagus

Question 15

Describe the function of the arytenoids and intrinsic laryngeal muscles

Answer 15

Majority of muscles act to narrow rima glottidis by adducting VCs together
Only posterior cricoarytenoid can abduct VCs (widens rima glottidis)
Arytenoids move relative to one another, alters position of true VCs & therefore size of aperture

Question 16

List the true vocal cord movements

Answer 16

Breathing – VCs abducted
Swallowing – VCs adducted
Phonation – VCs closely adducted, VC vibration creates sound waves
Cough – VCs strongly adducted

Question 17

Describe how different pitched sounds are produced

Answer 17

High-pitched sounds = vocal cords taut
Low-pitched sounds = vocal cords less taut
Contraction of both cricothyroid muscles = increases tension in vocal cords
-muscle located outside of larynx

Question 18

Describe the action of cricothyroid muscle

Answer 18

Tilts thyroid cartilage forward on cricoid increasing tension in vocal cords – important for reaching higher pitch
Innervated by external branch of superior laryngeal nerve (branch of vagus)
Nerve is closely related to superior thyroid artery – risk of injury in thyroid surgery
Causes hoarseness of voice when attempting higher pitched sounds

Question 19

Describe the larynx during swallowing

Answer 19

1) Tongue pushes epiglottis & aryepiglottic muscles contract -> narrows laryngeal inlet
2) Food/fluid directed over curved upper surface of epiglottis into piriform fossae of laryngopharynx (can be a site for foreign bodies to get stuck in)
3) Hyoid bone elevated & moved anteriorly by suprahyoid muscles (larynx moves up and forward)
4) Adduction of true vocal cords – closure of rima glottidis

Question 20

List the sensory and motor nerves supplying the larynx

Answer 20

Internal branch of superior laryngeal nerve – sensory: supraglottis & glottis (true VCs)
External branch of superior laryngeal nerve – motor: cricothyroid muscle
Recurrent laryngeal nerve – motor: intrinsic muscles & sensory: infraglottis

Question 21

Describe the route of the right and left recurrent laryngeal nerves

Answer 21

On right, passes anteriorly to and then loops under the right subclavian artery & on left, the arch of the aorta
Ascends in tracheo-oesophageal groove (behind lobes of thyroid gland)
Close anatomical relationship with thyroid gland & inferior thyroid arteries
Risk of damage to nerve in thyroid surgery = paralysis of muscles moving a true vocal cord

Question 22

How can the recurrent laryngeal nerve be injured?

Answer 22

Disease or surgery involving larynx, oesophagus or thyroid
Aortic arch aneurysm (left RLN)
Cancer involving apex of lung (right RLN)
RLN supplies intrinsic muscles of larynx responsible for vocal cord movements

Question 23

Describe a unilateral recurrent laryngeal nerve injury

Answer 23

Affected VC assumes a resting ‘paramedian’ position = between fully abducted and fully adducted
No significant impairment to airflow during breathing
Cannot adduct to meet VC opposite side – weak, ineffective cough & impaired phonation (hoarseness of voice)

Question 24

Describe a bilateral recurrent laryngeal nerve injury

Answer 24

Both VCs assume a resting ‘paramedian’ position
Significant airway obstruction – emergency surgical airway (neither VC can abduct during breathing to widen rima glottidis)