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Anatomy of the Larynx — Inside Out, Basic to Clinical

Note on Stamberger: The library database contains Scott-Brown, Cummings, and K.J. Lee's (the most practical ENT reference). Stamberger's Functional Endoscopic Sinus Surgery is available for sinus anatomy, but the larynx chapters in the database come from Scott-Brown and Cummings — all content below is directly from those authoritative ORL texts, supplemented by KJ Lee where it adds detail.

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1. OVERVIEW AND TOPOGRAPHY

• Angle of thyroid cartilage fusion: ~90° in men, ~120° in women
• AP diameter (post-puberty): ~36 mm in men, ~26 mm in women - largely due to the anterior-posterior doubling during male puberty

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2. FRAMEWORK OF THE LARYNX

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A. HYOID BONE

• A body anteriorly
• Greater cornua projecting backwards on each side
• Lesser cornua - small conical eminences on the upper lateral aspect of the body, joined by fibrous band or synovial joint

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B. THYROID CARTILAGE

• Fusion angle: ~90° men, ~120° women (hence more prominent in men)
• Posterior border of each lamina extends as superior cornu (long, narrow, curves up/back/medially - attached to lateral thyroid ligament) and inferior cornu (shorter, thicker, curves down/medially, articulates with cricoid via cricothyroid joint)
• Oblique line on the outer surface gives attachment to the inferior pharyngeal constrictor, sternothyroid, and thyrohyoid muscles
• The thyroid notch is at the upper border between the two laminae

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C. CRICOID CARTILAGE

• Arch - narrow anteriorly (~5–7 mm tall)
• Lamina - broad posteriorly (~20–30 mm tall)
• Articulates with: the inferior cornua of thyroid (cricothyroid joint - pivot joint allowing rocking/gliding) and with the arytenoid cartilages (cricoarytenoid joint - saddle joint allowing gliding/rotation)

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D. ARYTENOID CARTILAGES (paired)

• Apex - articulates with the corniculate cartilage above; points posteromedially
• Vocal process - projects anteriorly; gives attachment to the vocal ligament
• Muscular process - projects laterally; gives attachment to the PCA and LCA muscles
• Body - bears the cricoarytenoid joint surface inferiorly

• Rotation (abduction/adduction of vocal process)
• Gliding (anteroposterior and mediolateral) Combined movements determine glottic configuration.

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E. EPIGLOTTIS

• Leaf-shaped, elastic cartilage (does NOT ossify)
• Attached inferiorly to the back of the thyroid angle via the thyroepiglottic ligament
• Attached superiorly to the hyoid via the hyoepiglottic ligament
• The petiolus (stalk) is the narrow inferior end
• Perforations in the epiglottis allow tumour to enter the pre-epiglottic space

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F. MINOR CARTILAGES

• Corniculate (Santorini): Sits on the apex of the arytenoid; elastic cartilage; creates the corniculate tubercle seen endoscopically at the posterior laryngeal inlet
• Cuneiform (Wrisberg): Lies in the aryepiglottic fold anterior to corniculate; elastic cartilage; creates the cuneiform tubercle
• Cartilago triticea: Small nodule in the lateral thyrohyoid ligament (seen in the framework image above)

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3. LIGAMENTS AND MEMBRANES

Fibroelastic Membrane - TWO LAYERS:

• Spans from epiglottis/aryepiglottic fold down to the false cords
• Lower free border forms the vestibular (false cord) ligament
• Upper free border is the aryepiglottic fold

• Arises from the upper border of the cricoid arch
• Fans upward and medially
• Upper free border (thickened) = the vocal ligament
• Anteriorly - the cricothyroid ligament (median cricothyroid membrane) - the key surgical landmark for emergency airway access (cricothyroidotomy)

External Membranes:

• Thyrohyoid membrane: Connects hyoid to the upper border of the thyroid cartilage. Pierced by the internal branch of the SLN and the superior laryngeal artery. The lateral (free) portion is thickened as the lateral thyrohyoid ligament (may contain cartilago triticea)
• Cricothyroid membrane: Between thyroid and cricoid anteriorly - the surgical landmark

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4. INTERNAL ANATOMY - THE THREE REGIONS

SUPRAGLOTTIS

• Extends from the epiglottis/aryepiglottic folds superiorly to a horizontal line through the apex of the laryngeal ventricle inferiorly
• Includes: (1) epiglottis (suprahyoid and infrahyoid portions), (2) aryepiglottic folds, (3) arytenoids, (4) false (vestibular) cords, (5) ventricle
• Embryological note: The supraglottis has a separate embryological origin from the glottis/subglottis - this explains why supraglottic and glottic cancers have different lymphatic drainage patterns

GLOTTIS

• From the ventricle apex to 5 mm below the free edge of the true vocal folds (or 1 cm below the ventricle apex)
• Includes: true vocal cords, anterior commissure, posterior commissure

SUBGLOTTIS

• From the lower boundary of the glottis to the inferior margin of the cricoid cartilage
• Anterior commissure (Broyle's tendon): The lower edges of the vocal folds converge anteriorly. Broyle's ligament attaches the vocal folds to the inner thyroid cartilage here - there is no perichondrium at this point, meaning tumour can invade the cartilage directly. Also, Broyle's ligament connects to the subglottis via the apex of a triangle with the epiglottis, so anterior commissure tumours readily involve the subglottis.

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5. VOCAL FOLD - LAYERED STRUCTURE

• Anterior 3/5 (anterior commissure to tip of vocal process) = membranous part - where vibration and pathology mainly occur
• Posterior 2/5 (vocal process to arytenoid face) = cartilaginous part

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6. THE LARYNGEAL VENTRICLE AND SACCULE

• The ventricle (of Morgagni) is the fusiform recess between the false cord above and the true cord below
• The saccule (appendix) is an upward diverticulum from the anterior part of the ventricle, projecting superolaterally between the vestibular fold and inner thyroid cartilage
• The saccule is lined with mucous glands that lubricate the vocal folds (which themselves have NO glands)
• Fibrous tissue surrounds the saccule
• Clinical: Dilatation of the saccule → laryngocele. Causes: increased intraglottic pressure (horn players, glass blowers) OR obstruction by inflammatory/neoplastic lesion. An internal laryngocele stays within the paraglottic space; an external (mixed) laryngocele pierces the thyrohyoid membrane and presents as a neck mass. The saccule can harbour occult cancers - must be actively inspected during diagnostic endoscopy.

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7. SPACES WITHIN THE LARYNX

PRE-EPIGLOTTIC SPACE (PES)

• Wedge-shaped, point inferiorly
• Bounded: anteriorly by the thyrohyoid membrane/hyoid; posteriorly by the epiglottis
• Superiorly: hyoepiglottic ligament
• Tumour enters through perforations in the epiglottis or through the hyoepiglottic ligament
• Continuous laterally with the paraglottic space (no anatomical boundary between them)

PARAGLOTTIC SPACE (PGS)

• Bounded: laterally by thyroid cartilage; medially by conus elasticus + quadrangular membrane; posteriorly by piriform fossa mucosa
• Contains the laryngeal ventricle and saccules
• Tumours may spread extensively in this space with minimal mucosal changes - this is why submucosal tumour spread can be missed on endoscopy
• The paraglottic and pre-epiglottic spaces communicate freely - explaining why supraglottic cancers can cross midline via the pre-epiglottic space

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8. MUCOUS MEMBRANE AND EPITHELIUM

• Closely adherent (prone to perichondritis if inflamed): over posterior surface of epiglottis, corniculate/cuneiform cartilages, and over the vocal ligament
• Loosely adherent (prone to oedema): everywhere else - e.g. the aryepiglottic folds, false cords → this is why supraglottic oedema (angioedema, epiglottitis) can be life-threatening

• Pseudostratified ciliated columnar epithelium ("respiratory" type): Most of the larynx
• Non-keratinizing stratified squamous epithelium: Upper half of posterior epiglottis, upper aryepiglottic fold, posterior glottis, and the vocal folds themselves

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9. INTRINSIC MUSCLES OF THE LARYNX

• PCA: ~equal type 1 and type 2A (aerobic, fatigue-resistant; peak contraction ~40 ms)
• TA: ~40% type 1, 55% type 2A, 5% type 2B
• LCA: fast (peak ~19 ms)
• CT: majority type 1 (aerobic) - peak ~50 ms

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10. EXTRINSIC MUSCLES

• Inferior constrictor: arises from oblique line of thyroid cartilage - its lowermost circular fibres = cricopharyngeus (upper oesophageal sphincter), attaching to posterolateral cricoid. Clinically important in dysphagia and Zenker's diverticulum.

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11. NERVE SUPPLY

Superior Laryngeal Nerve (SLN)

• Arises from the inferior (nodose) ganglion of the vagus
• Receives a branch from the superior cervical sympathetic ganglion
• Descends lateral to the pharynx, behind the internal carotid artery
• At the level of the greater horn of the hyoid, divides into:

• Innervates cricothyroid muscle
• Also innervates inferior constrictor
• Runs close to the superior thyroid artery near the upper thyroid pole → at risk during thyroidectomy (Joll's triangle)
• Injury: loss of high-pitched voice, inability to project voice, vocal fatigue

• Larger
• Pierces the thyrohyoid membrane just above the superior laryngeal artery
• Upper branch: mucosa of lower pharynx, epiglottis, valleculae, vestibule
• Lower branch: descends in the medial wall of the piriform fossa beneath mucosa → aryepiglottic fold + laryngeal mucosa down to the level of the vocal folds
• Carries afferent fibres from neuromuscular spindles and stretch receptors
• Ends by piercing the inferior constrictor and unites with ascending RLN branch = Galen's anastomosis (purely sensory)
• Clinical use: SLN block can be achieved by injecting local anaesthetic at the piriform fossa mucosa - provides excellent anaesthesia for awake fibreoptic intubation

Recurrent Laryngeal Nerve (RLN)

• Motor to ALL intrinsic muscles except cricothyroid
• Sensory below the vocal folds

• Right RLN: Loops around the right subclavian artery, ascends in the tracheo-oesophageal groove
• Left RLN: Longer course - loops around the aortic arch (at the level of the ligamentum arteriosum), ascends in the tracheo-oesophageal groove

• Left RLN: more likely posterior to the artery
• Right: equal chance in any of three positions relative to artery
• Up to 30% of RLNs branch extralaryngeally before entering - increases injury risk

• Lateral approach (safest): Beahr's triangle - inferior thyroid artery (superior), trachea (medial), common carotid artery (lateral)
• Superior approach: At cricothyroid junction - useful in cancer surgery, reoperations, or when non-recurrent RLN is suspected

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12. BLOOD SUPPLY

Arterial

1. Superior laryngeal artery - branch of superior thyroid artery - passes deep to the thyrohyoid muscle, pierces the thyrohyoid membrane with the internal SLN to supply the upper larynx
   • Risk during endoscopic supraglottic resections as it enters the paraglottic space at the anterior end of the aryepiglottic fold
2. Inferior laryngeal artery - branch of inferior thyroid artery - ascends on the trachea with the RLN, enters the larynx beneath the lower border of the inferior constrictor
3. Cricothyroid artery - branch of superior thyroid artery - crosses the upper part of the cricothyroid ligament (up to 5 branches). Can be injured during cricothyroidotomy or during resection of anterior commissure cancers.

Venous

• Superior laryngeal veins → superior thyroid or facial vein → internal jugular vein
• Inferior laryngeal veins → inferior thyroid veins → brachiocephalic vein

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13. LYMPHATIC DRAINAGE

• Glottic cancers (T1/T2) rarely have nodal metastases - voice change causes early presentation
• Supraglottic cancers present late and have bilateral nodal drainage (midline structures drain bilaterally)
• Subglottic cancers drain to Level VI - paratracheal dissection required

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14. RADIOLOGICAL ANATOMY

• The anterior commissure may approach within 1 cm of the skin surface - important for radiation planning
• Vocal cords attach to thyroid cartilage at the "figure-of-eight" appearance on plain lateral film
• Anatomical boundaries of supraglottis, glottis and subglottis are readily visualised on lateral X-ray

• Thyroid, cricoid, most of arytenoid body = hyaline cartilage - ossifies from ~age 20 → radiopaque, visible on CT bone windows
• Epiglottis, corniculate, cuneiform cartilages, apex and vocal process of arytenoid = elastic cartilage - does NOT ossify → NOT radiopaque

• Ossified cartilage: CT highly sensitive for frank cortical destruction (irregular erosion, sclerosis, or lysis)
• Non-ossified cartilage: CT less reliable for invasion - use MRI

• Pre-epiglottic fat, paraglottic fat, aryepiglottic fold fat - critical landmarks on axial CT/MRI for assessing deep invasion
• Loss of fat plane = tumour spread into that space

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15. CLINICAL APPLIED SUMMARY

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• Scott-Brown's Otorhinolaryngology Head & Neck Surgery, Vol 2, Chapter 58 (p. 928–937)
• Cummings Otolaryngology Head and Neck Surgery, Chapters 8 & 110 (pp. 180, 723–734, 2124–2126)
• K.J. Lee's Essential Otolaryngology, Chapter on Larynx (pp. 909–912)