Anatomy of larynx

ANATOMY OF LARYNX AND TRACHEOBRONCHIAL TREE

Guide: Dr. Bhanu Chaudhary MD Presented by, Professor & Head of Department Dr. Ranjith kumar Dept of Anaesthesiology PG Resident

G.R.Medical college Gwalior.

Respiratory System

Descriptive Anatomy - Larynx

Situation & Extent:

– Lies in anterior midline of neck

– Opp to C3 to C6 vertebra in men

– Level is higher in female & children

Infants b/w 6 and 12 months of age - the tip of the epiglottis lies little above the level of fibrocartilage b/w the odontoid process and body of the axis.

SIZE

According to Sappey the average measurements of the adult larynx are as follows:

In Males In Females.Length 44 mm. 36 mm.

Transverse diameter 43 mm. 41 mm.

Antero-posterior diameter 36 mm 26 mm.

Circumference 136 mm. 112 mm.

Until puberty there is little difference b/w male & female larynx.

After puberty - male larynx undergoes considerable increase; all the cartilages are enlarged and the thyroid cartilage becomes prominent in the middle line of the neck.

General principles of development

The development of the larynx - prenatal and postnatal stages.

At birth - larynx is located high in the neck b/w C1 and C4 vertebrae, allowing concurrent breathing or vocalization and deglutition.

At 2 years - larynx descends inferiorly;

At 6 years - reaches the adult position between C4 and C7 vertebrae.

This new position provides a greater range of phonation (because of the wider supraglottic pharynx) at the expense of losing this separation of function, i.e., deglutition and breathing.

Embryology

• Larynx - develops from endodermal lining and the adjacent mesenchyme of the foregut b/w the 4 & 6th branchial arches.

• At 20 days' gestation - the foregut is first identifiable with a ventral laryngotracheal groove. It continues to deepen until its lateral edges fuse.

• Trachea becomes separated from the esophagus by the tracheoesophageal septum with a persistent slit like opening into the pharynx

• Fusion occurs in the caudal-to-cranial direction, and incomplete fusion results in development of persistent communication between the larynx or trachea and the esophagus(tracheoesophageal fistula)

The main changes occurring in the larynx postnatally are a change in the axis, luminal shape, length, and

proportional growth of the laryngeal elements.

The larynx grows rapidly during the first 3 years of life.

The larynx elongates as the hyoid, thyroid, and cricoid cartilages separate from each other.

The cricoid cartilage continues to develop during the first decade of life, gradually changing from a funnel shape to a wider adult lumen; therefore, it is no longer the narrowest portion of the upper airway.

Larynx - Structure

Constituents of larynx

• 9 Cartilages– 3 paired– 3unpaired

• 8 Muscles(Intrinsic)

• Ligaments

Cartilages of Larynx

3 Unpaired cartilages• Thyroid• Cricoid• Epiglottis

3 Paired cartilages• Arytenoid• Corniculate• Cuneiform

Histology: Hyaline – Thyroid, Cricoid & base of Arytenoids are Hyaline.

May ossify after 25 yrs of age Other cartilages are Elastic & they do not ossify.

Thyroid Cartilage

• Shield shaped, open posteriorly, angulated anteriorly.

• Largest cartilage of larynx

• Angulation more acute in males(90) & in females it is 120.

• Its function is to shield larynx from injury and provide an

attachment to vocal cords

Cricoid Cartilage

• Signet ring shaped

• Stronger than thyroid cartilage.

• Narrow ant part - arch

• Broad post part - lamina

Important from structural & functional point of view

– Base for entire larynx

– Support to arytenoid

– Attachment to intrinsic muscles

– Only part of cartilagenous framework that forms continuous 360

degree ring

The narrowest portion of the airway in an infant.We use this fact when ventilating infants as infant ET tubes do not have cuffs to seal the trachea

Epiglottis

• Thin leaf shaped fibro-cartilage, situated in midline

• Upper free end broad & rounded, projects up behind base

of tongue

• Spoon-shaped cartilage prevents aspiration by covering

the opening of the larynx during swallowing.

• The tongue and the epiglottis are connected by folds �of mucous membranes which form a small space called

the vallecula.

Vallecula

Arytenoids

• Paired cartilages, pyramidal in shape

• Base articulated with cricoid• PCA & LCA muscles attach on

muscular process• Anterior angle elongated into

vocal process which receives insertion of vocal ligament

Paired cartilages

Laryngeal compartments

1. Glottis or superior vestibule

2. Supraglottis or

ventricle/sinus of larynx

3. subglottis

Supraglottis

• Consists of ventricles, false

cords, laryngeal surface of

epiglottis & aryepiglottic folds .

• Vestibular folds- narrow band of

fibrous tissue passing from

anterolateral surface of arytenoid

to angle of thyroid cartilage.

• Separated from true vocal cords

by larngeal sinus.

Glottis or superior vestibule• Consists of true cords, anterior commissure

and posterior commissure.

• Vocal cords – 2 pearly white folds of mucous

membrane stretching from angle of thyroid

cartilage to vocal process of arytenoid.

• Narrow triangular space between the true

cords is called rima glottis.

• Anterior 2/3 is membranous

• Posterior third consists of vocal processes of

arytenoids.

• Posterior 1/3 of cords and covering mucosa

are called posterior commissurePearly white – since there is no true submucosa with usual network of blood vessels

Sub-glottis

• Begins about 5mm below free

margins of Vocal cord.

• Extends from vocal folds to the

lower border of cricoid cartilage.

• Consists of a mobile upper and

fixed lower part.

• Narrowest part of laryngeal cavity

in children under 10 years of age.

Clinical significance – During intubation in small children an ET tube can pass between vocal cord may yet too large to pass beyond cricoid ring

Mucosa

• Mucosa of glottic and Supraglottic regions is stratified

squamous epithelium.

• Mucosa of ventricles and sub-glottic regions is pseudo-

stratified ciliated epithelium.

• Supra and sub glottic regions particularly ventricles are rich in

submucosal mucous or minor salivary glands while glottis is

not.

Muscles of Larynx

Intrinsic:

Cricothyroid

Posterior cricoarytenoid

Lateral cricoarytenoid

Transverse arytenoid

Oblique arytenoid

Aryepiglotticus

Thyroarytenoid

Thyroepiglotticus

Vocalis

Extrinsic:

(connect larynx to its neighbour)

Sternothyroid – Depresses

larynx.

Throhyoid – Elevates larynx.

Inferior constrictor

Action of muscles

open close

Glottis Posterior Cricoarytenoid Lateral cricoarytenoidTransverse arytenoid Cricothyroid Thyroarytenoid

Laryngeal inlet Thyroepiglotticus Oblique arytenoid Aryepiglotticus

Vocal folds Cricothyroid(Tense) Thyroarytenoid & Vocalis(Relax)

Cricothyroid Muscle

Adductors of the Vocal Folds

Abductor of Larynx

Laryngeal Ligaments

A series of intrinsic ligaments binds all 9 cartilages together to form the larynx.

Extrinsic ligaments attach the thyroid cartilage to the hyoid bone and the cricoid cartilage to the trachea.

The vestibular ligaments and the vocal ligaments extend between the thyroid cartilage and the arytenoids.

The vestibular and vocal ligaments are covered by folds of laryngeal epithelium that project into the glottis.

Ligaments of Larynx

Ligaments Cont…

The vestibular folds, which are relatively inelastic, help prevent foreign objects from entering the glottis and provide protection for the more delicate vocal folds.

The vocal folds are highly elastic, because the vocal ligament is a band of elastic tissue.

The vocal folds are involved with the production of sounds hence known as the true vocal cords.

Because the vestibular folds play no part in sound production - called the false vocal cords.

Blood Supply

These vessels accompany superior and recurrent laryngeal nerves

Sup.laryngeal vein drains into Sup.Thyroid Vein

Inf.laryngeal vein drains into Inf. Thyroid veins

Lymphatic drainage

Above vocal folds – Antero superior group of Deep cervical nodes.

Below Vocal folds – Postero inferior group of deep cervical nodes through prelaryngeal & pretracheal nodes.

Nerve Supply: Derived from the Vagus• Superior Laryngeal Nerve -It leaves

the vagus nerve high in the neck– Internal - provides sensation of

the glottis and supraglottis, which includes the pharynx, underside of the epiglottis and the larynx above the cords.

– External -It supplies motor function to the cricothyroid muscle which tenses the vocal cords and could cause laryngopasm.

• Recurrent Laryngeal Nerve - provides sensation to the subglottic area which includes the larynx below the vocal cords and upper esophagus. Motor function to most of intrinsic muscles of the larynx

• It branches from the vagus in the mediastinum and turns back up into the neck. On the right, it travels inferior to the subclavian and loops up, and on the left it travel inferior to the aorta and loops up.

Motor nerves :All the muscles of larynx are supplied by the recurrent laryngeal nerve except cricothyroid which is supplied by external laryngeal nerve�Sensory nerves :Internal laryngeal nerve-upto level of vocal fold

Reccurent laryngeal nerve-below vocal fold

Position of vocal cord in health &disease

Positon of cordLocation of cord

from midline

Situations in

health disease

Median Midline Phonation RLN paralysis

Paramedian 1.5 mm Strong whisperRLN paralysis

Intermediate(cadaveric)

3.5 mm. (This is neutral position of cricoarytenoid joint. Abduction and adduction takes place from this position.)

-Combined paralysis ( both RLN & SLN)

Gentle abduction 7 mm Quiet respiration Paralysis of adductors

Full abduction 9.5 mm Deep inspiration -

Vocal cord

The opening into trachea is maximum at the end of deep inspiration.In order to minimise the risk of trauma to voca cords Intubation and Extubation should be carried out during inspiration

Types Of Vocal cord Paralysis

Unilateral Abductor Paralysis

Bilateral Abductor Paralysis

Unilateral Adductor Paralysis

Bilateral Adductor Paralysis

RLN Paralysis• It carries fibres for both abductor and adductor muscles of larynx.• Injury – partial or complete• Abductor fibres - more vulnerable even for mild injury

Moderate trauma produces only abductor paralysis.

Severe injury or section of nerve produces both abductor and adductor paralysis.

Semon's law: This theory proposed by Rosenbach and Semon in 1881, depends on the concept that abductor fibres in the recurrent laryngeal nerves are more susceptible to pressure than the adductor fibers.

Wagner and Grossman theory (1897).: most popular and widely accepted theory, states that in complete paralysis of RLN the cord lies in the paramedian position because the intact cricothyroid muscle adducts the cord. (Because the superior laryngeal nerve is intact).

If the superior laryngeal nerve is also paralysed the cord will assume an intermediate position because of the loss of adductive force.

Unilateral Abductor Paralysis

Paralysis of recurrent laryngeal nerve.

Vocal cord lies in median or paramedian position, doesn’t move on

deep inspiration.

Initial hoarseness.

No regurgitation.

Vocal cord compensation occurs leading

to improvement of voice.

Bilateral Abductor Paralysis

Paralysis of both recurrent laryngeal nerves.

Thyroid surgery - cause

Both vocal cord lies in paramedian position

due to unopposed action of cricothyroid.

Severe dyspnoea and stridor.

Voice is good and there is no regurgitation

Vocal cord compensation may occurs leading to improvement

Immediate tracheostomy & various procedures for Lateralisation of

cord.

Unilateral Adductor Paralysis

1.Paralysis of both superior and recurrent laryngeal nerves

2. Vocal cord lies in Lateral (cadaveric) position

3. Weak husky voice

4. There is aspiration of food and fluid

5. Vocal cord compensation occurs leading to improvement of voice

Medialization of vocal cord or reverse cordopexy ---- Treatment

Bilateral Adductor Paralysis

1. Paralysis of combined both recurrent and superior laryngeal nerves

2. Psychiatric Illness or widespread neurological lesion or neoplastic lesion

in the base of skull, upper neck etc.

3. Both vocal cord lies in lateral (cadaveric) position

4. Severe regurgitation of food and fluid.

5. Voice is breathy

6. Vocal cord compensation may occurs leading to improvement

7. If compensation does not occur than total laryngectomy and

epiglottopexy ---- Treatment

TRACHEA

It is a cartilaginous & membranous tube,10 - 11cm long & 2.5cm(1 inch) in diameter.

Cartilages – deficit posteriorly. Extend from lower border of cricoid cartilage(C6) to carina(T5)

where it bifurcates into right & left main bronchus. Lined by ciliated columnar epithelium Trachea moves upward during swallowing, & downward

forward during inspiration.

Extension of head & neck can increase the length of the trachea by as much as 23 to 30 %.

TRACHEOBRONCHIAL TREE

Bronchiole

Respiratory Bronchioles

Alveolar Ducts

Pulmonary Atria

Alveolar sac & Pulmonary Alveoli

Terminal Bronchioles

Dichotomous division – starting with trachea & ending in alveolar sacs (23 generations)First 16 generation – only conductiveLast 7 generation – Respirative (involves in gas exchange)

Right main bronchus:• 5 cm long, wider,

shorter & more vertical then the Lt main bronchus.

• It makes 25-300 with carina

Left main bronchus:• 5.5cm long,2-

3mm narrower then the Right main bronchus.

• more horizontal & making an angle of 450 with trachea

Rt main bronchus – since it is more vertical there is much greater tendency for ET tubes or Suction catheters to enter this lumen.In small children <3yrs of age - angulation of 2 main bronchi at the carina is equal on both sides.

Bronchopulmonary segments

Aspiration pneumonitis• Aspiration pneumonitis (Mendelson’s syndrome) is a chemical injury

caused by the inhalation of sterile gastric contents.• A reduced level of consciousness can lead to an unprotected airway. If

the patient vomits they can aspirate the vomitus contents into their lungs. This can set up lung inflammation with infection.

• Also occur in spinal anaesthesia if the level of spinal block is too high, leading to paralysis or impairment of the vocal cords and respiratory impairment.

• Most authors agree that a pH < 2.5 and a volume of gastric aspirate greater than 0.3 ml per kilogram of body weight (20 to 25 ml in adults) are required for the development of aspiration pneumonitis.

• Aspiration of particulate food matter from the stomach may cause severe pulmonary damage, even if the pH of the aspirate is above 2.5.

Risk factor of aspiration

• Gastric oro-esophageal disease state.

• Incompetent lower esophageal sphincter .

• Emergency surgery.

• Drugs decreasing esophageal sphincter tone. (opioids , anticholinergics, benzodiazepines, thiopentone , volatile agents.)

• Obesity.,Diabetes, peptic ulcer disease, stress, pain & trauma.

Location

Patients who aspirate

In a lateral position, the inhaled materials tends to gravitate into the lateral portion of posterior segment of upper lobe.

In supine position, the material accumulates in the apical segment of lower lobe.

When patient is propped up in post operative period, secretions tend to gravitate to the lower lobes.

Prevention

• Use regional technique, awake intubation.

• Ensure empty stomach.(Fasting)

• Inhibit secretion of gastric acid .

• Rapid sequence induction. (sellick maneuver)

• Extubate when pt fully awake.

Fasting RecommendationsIngested Material Minimum Fasting Period

• Clear liquids 2 h• Breast milk 4 h• Infant formula 6 h• Nonhuman milk 6 h• Light meal 6 h

Examples of clear liquids include water, fruit juices without pulp, carbonated beverages, clear tea, and black coffee.

Brian A Sellick 1918-1996, London Anaesthetist

"Cricoid pressure must be exerted by an assistant.

Before induction, the cricoid is palpated and lightly held between the

thumb and second finger.

As anaesthesia begins, pressure is exerted on the cricoid cartilage

mainly by the index finger. Even a conscious patient can tolerate

moderate pressure without discomfort but as soon as consciousness is

lost, firm pressure can be applied without obstruction of the patient's

airway.

Pressure is maintained until intubation and inflation of the cuff of the

endotracheal tube is complete.”

Essential Elements of Cricoid Pressure

• Must apply force to the cricoid cartilage

• Must apply force in correct direction

• Must apply correct amount of force

• Must apply force for correct duration of time

How Much Force?

• A force of 30 N (3 kg) is recommended for an unconscious patient”

Clayton TJ, Vanner RG. A novel method of measuring cricoid force. Anaesthesia. 2002;57:326-9.

Thank you