Larynx_pdf.pdf

Larynx MD3001 September 2023 Dr. Alex Gardner [email protected] Learning Outcomes By the end of this lecture, time spent in the dissecting room, and further private study you should be able to: 1. Describe the general structure and functions of the larynx 2. Describe the cartilages and membr...

Larynx MD3001 September 2023 Dr. Alex Gardner [email protected] Learning Outcomes By the end of this lecture, time spent in the dissecting room, and further private study you should be able to: 1. Describe the general structure and functions of the larynx 2. Describe the cartilages and membranes of the larynx 3. List the extrinsic muscles of the larynx 4. Describe the actions of the intrinsic muscles of the larynx 5. Describe (briefly) the neurovascular supply of the larynx (more detail will come in MD 4001) 6. Discuss the clinical conditions that may affect the larynx, particularly in relation to nerve lesions MD3001 2023 2 Sources N.B. Consult chapters on thorax, head and neck MD3001 2023 3 What is the larynx? • Membranous tube of cartilage, muscle and fibrous membranes (ligaments and folds) • Connects oropharynx with trachea, via laryngeal inlet MD3001 2023 4 Larynx functions • Conduct air • Protect the airway from food, liquids etc. • Vocalisation MD3001 2023 5 Larynx location • • • • Anterior, median neck Laryngeal inlet at C3 level Trachea begins C6 level Laryngeal prominence palpable below skin • Mobile during function • Higher in newborn and infants, descending weeks 4-6 https://www.researchgate.net/publication/279250533_Current_Updates_on_Choanal_Atresia MD3001 2023 6 Larynx structure • Inferior to hyoid bone, via thyrohyoid membrane • Thickened membrane = median thyrohyoid ligament, and paired lateral thyroid ligaments MD3001 2023 7 Larynx structure - cartilages • Three large unpaired cartilages • Four pairs of smaller cartilages • All hyaline cartilage except the epiglottis, which is elastic cartilage MD3001 2023 Thyroid Epiglottis Arytenoids cricoid 8 Larynx structure - cartilages • Three large unpaired cartilages • Four pairs of smaller cartilages • Triticeal cartilages may be present within lateral thyrohyoid ligament (1/3 of people) MD3001 2023 9 Larynx structure - cartilages • Thyroid cartilage Connects to • Hyoid superiorly • Cricoid cartilage inferiorly • Epiglottis on posterior aspect of laryngeal prominence • Arytenoids via vocal and vestibular ligaments MD3001 2023 10 Larynx structure - cartilages Male MD3001 2023 Female 11 Larynx structure - cartilages • Cricoid cartilage Connects to • Thyroid superiorly • Trachea inferiorly Anterior Articulates with • Inferior horn of thyroid • Arytenoid cartilage • Synovial joints MD3001 2023 12 Larynx structure - cartilages • Epiglottic cartilage • Elastic cartilage, attaches to thyroid cartilage via thyroepiglottic ligament • Attached to hyoid bone via Hyoepiglottic ligament MD3001 2023 13 Larynx structure - cartilages • Arytenoid cartilages • Pyramid shaped • Base sits on cricoid cartilage, medial surfaces face each other • Corniculate cartilage sits on apex • Depression on anterolateral surface for vestibular ligament and vocalis muscle MD3001 2023 14 Larynx structure - cartilages • Corniculate cartilages – sit atop arytenoids • Cuneiform cartilages – sit within quadrangular membrane MD3001 2023 15 Larynx structure – Membranes and ligaments Extrinsic ligaments • Hyo-epiglottic ligament • Cricotracheal ligament • Thyrohyoid membrane (median and lateral thickening = ligaments) – Fibro-elastic – Pierced by internal branch of superior laryngeal nerve and superior laryngeal vessels MD3001 2023 16 Larynx structure – Membranes and ligaments Intrinsic ligaments • Fibroelastic membrane = quadrangular membrane + conus elasticus • Vocal ligament forms true vocal fold (cord) • Vestibular ligament forms false vocal fold (cord) MD3001 2023 17 Larynx structure – Membranes and ligaments • Cartilages and membranes covered by mucosa • Vestibular and vocal folds divide the larynx into vestibule, ventricle and infraglottic space • Anterior aspect of ventricles = saccule, lubricates vocal cords • Aryepiglottic folds form lateral borders of laryngeal inlet • Vocal folds = stratified non keratinising squamous epithelium • Space between vocal folds is the rima glotiddis MD3001 2023 18 Larynx structure – Muscles Extrinsic muscles • Pharyngeal elevators • Stylopharyngeus • Palatopharyngeus • Salpingopharyngeus • Suprahyoid muscles • Infrahyoid muscles MD3001 2023 19 Larynx structure – Muscles Extrinsic muscles • Laryngeal elevators are digastric, mylohyoid, stylohyoid, geniohyoid and thyrohyoid • Infrahyoid muscles mostly depress larynx – sternohyoid, thyrohyoid, sternothyroid • Thyrohyoid function varies on whether hyoid bone is fixed Elevation of the larynx during swallowing is a key step in protection of the airway MD3001 2023 20 Larynx structure – Muscles Functions are • protection /closure of airway • controlling size of rima glottidis • Altering tension of vocal ligaments • Mostly named after the cartilages they attach to • Innervation is by the recurrent laryngeal nerve (vagus) except cricothyroid muscle MD3001 2023 21 Larynx structure – Muscles Functions are • protection /closure of airway • Oblique arytenoids • Posterior surface of muscular process of one arytenoid to the posterior apex of the other • Fibres also extend into the ary-epiglottic fold • Purse-string like effect • Sphincter of laryngeal inlet MD3001 2023 22 Larynx structure – Muscles Functions are • protection /closure of airway • Thyro-arytenoid • Thyroid angle and cricothyroid ligament to anterolateral surface of arytenoid cartilage • Fibres also extend into the ary-epiglottic fold to lateral margin of epiglottis • Sphincter of laryngeal inlet and vestibule MD3001 2023 23 Larynx structure – Muscles Functions are • Controlling diameter of rima glottidis • Posterior crico-arytenoid • Posterior surface of lamina of cricoid cartilage to posterior surface of muscular process of arytenoid cartilage • Abduct vocal folds via external rotation of arytenoids – main openers of rima glottidis MD3001 2023 24 Larynx structure – Muscles Functions are • Controlling diameter of rima glottidis • Lateral crico-arytenoid • Superior surface of arch of cricoid cartilage to anterior surface of muscular process of arytenoid cartilage • Adduct vocal folds via internal rotation of arytenoids closing rima glottidis MD3001 2023 25 Larynx structure – Muscles Functions are • Controlling diameter of rima glottidis • Transverse arytenoid • Lateral borders of posterior surfaces of arytenoid cartilages • Adduct arytenoid cartilages MD3001 2023 26 Larynx structure – Muscles Functions are • Controlling diameter of rima glottidis • Vocalis • Lateral surface of vocal process of arytenoid cartilage to vocal ligament and thyroid angle • Adjust tension in vocal ligaments MD3001 2023 27 Larynx structure – Intrinsic Muscles Cricothyroid • Inferior horn and margin of thyroid cartilage to arch of cricoid cartilage • Rotates thyroid cartilage antero-inferiorly • Lengthens and thus tightens vocal folds • External branch of superior laryngeal nerve (Vagus/CN X) • ALL other intrinsic laryngeal muscles are innervated by the recurrent laryngeal nerve MD3001 2023 28 Intrinsic laryngeal muscles - superior view MD3001 2023 29 Intrinsic laryngeal muscles - superior view Posterior crico-arytenoid lateral crico-arytenoid active with oblique and transverse arytenoids relaxed Muscles relaxed Oblique and transverse arytenoids AND lateral crico-arytenoid Stronger contraction leads to Valsalva manoeuvre MD3001 2023 30 Larynx – closure and airway protection • A complex subconscious process involving coordination of the various intrinsic and extrinsic muscles • Elevation of larynx • Adduction of vocal folds • Approximation of vestibular folds • Constriction of laryngeal inlet • Anterior movement of arytenoids • Epiglottic inversion MD3001 2023 31 Larynx innervation • Vagus nerve (CN X) • Superior laryngeal • Internal branch = sensory above vocal cords • External branch = motor to cricothyroid • Recurrent laryngeal -> inferior laryngeal = motor to all other laryngeal muscles and sensory to vocal cords and below • Note what structures the recurrent laryngeal nerve loops around MD3001 2023 32 Larynx – arterial supply • Superior laryngeal arteries (from superior thyroid from ECA) • Inferior thyroid arteries (from thyrocervical trunk, from subclavian) MD3001 2023 33 Larynx – Venous drainage • Superior laryngeal veins > superior thyroid veins -> internal jugular veins • Inferior laryngeal veins -> inferior thyroid veins -> brachiocephalic veins • Depictions vary – sometimes left brachiocephalic vein only MD3001 2023 34 Larynx – lymphatics • Above vocal folds -> superior deep cervical nodes • Below vocal folds -> pre and paratracheal nodes -> inferior deep cervical nodes MD3001 2023 35 Clinical considerations • Choking • Anaphylaxis • Laryngospasm • Aspiration pneumonia • Cricothyroidotomy • Recurrent laryngeal nerve damage MD3001 2023 36 Clinical considerations Choking – emergency requiring clearance of obstruction • RESUS council UK management • Encourage cough, back blows, abdominal thrusts https://www.resus.org.uk/sites/default/files/2021-04/Adult%20Choking%20Algorithm%202021.pdf MD3001 2023 37 Clinical considerations Anaphylaxis • Can affect airways at multiple levels • Laryngeal angioedema, first instance requires epinephrine MD3001 2023 38 Clinical considerations Cricothyroidotomy • Gain access to the airway in an emergency situation • Cricothyroid membrane is relatively superficial • Vertical incision in skin to avoid anterior jugular veins, then transverse incision in cricothyroid membrane https://www.cambridge.org/core/books/color-atlas-of-emergencytrauma/cricothyroidotomy/3BE48197A011ED7E2A52D3A8356696DB MD3001 2023 39 Clinical considerations Recurrent laryngeal nerve damage • Iatrogenic e.g. thyroid surgery • Neurological • Compression via tumour • Causes hoarseness/vocal cord paralysis • If unilateral, other cord can compensate for phonation • Complete bilateral RLN damage will mean phonation is not possible • Partial damage affects abductors more than adductors, leading to median position of cords and increased dyspnoea https://www.omicsonline.org/vocal-cord-dysfunction-an-updated-review-2161-119X.S1-002.php?aid=2928 MD3001 2023 40 Clinical considerations Laryngospasm • Stimulation of internal superior laryngeal fibres triggering reflex closure of airway • Can be a surgical/anaesthetic consideration triggering inappropriate laryngeal closure reflex • Can also occur in neurological conditions Aspiration pneumonia • Compromised swallowing co-ordination (dysphagia) often due to stroke or other neurological condition • Food/drink can be inhaled and lead to infection • May require dietary changes e.g. thickening agents MD3001 2023 41 EMQ style Q • The larynx consists of several cartilages. Which laryngeal cartilage is composed of elastic cartilage? • Arytenoid • Thyroid • Cricoid • Epiglottic • Corniculate 42 SAQ style Q • A patient reports a hoarse voice after thyroid surgery. Suggest how this could occur? (3 marks) • The recurrent laryngeal nerve is in close association with the thyroid gland and can be damaged during thyroid surgery • The recurrent laryngeal nerve supplies intrinsic laryngeal muscles that control the vocal ligaments/cords • Damage to the recurrent laryngeal nerve therefore results in a hoarse voice or loss of voice 43