Larynx

The larynx, commonly known as the voice box, is a vital organ located in the anterior neck. It serves multiple functions including voice production, airway protection, and facilitation of respiration. Understanding its anatomy and relationships is essential for both clinical assessment and surgical procedures.

Anatomy of the Larynx

Gross Anatomy

• Location and relations in the neck: The larynx is situated between the pharynx and trachea, anterior to the C3–C6 vertebrae. It is closely related to the thyroid gland, carotid arteries, and cervical vertebrae.
• Dimensions and orientation: In adults, the larynx is approximately 4–5 cm in length, with its axis slightly tilted posteriorly. It is narrower in the anterior-posterior dimension and wider transversely.

Cartilages

• Thyroid cartilage: The largest cartilage, forming the anterior framework and giving rise to the laryngeal prominence.
• Cricoid cartilage: A complete ring located inferior to the thyroid cartilage, providing support and attachment for laryngeal muscles.
• Arytenoid cartilages: Paired pyramidal structures that anchor the vocal cords and facilitate their movement.
• Epiglottis: Leaf-shaped cartilage that covers the laryngeal inlet during swallowing to prevent aspiration.
• Other minor cartilages: Corniculate and cuneiform cartilages support the aryepiglottic folds and maintain airway patency.

Muscles

• Intrinsic muscles: Control vocal cord tension and opening/closing of the glottis, including thyroarytenoid, cricothyroid, and lateral cricoarytenoid muscles.
• Extrinsic muscles: Position and stabilize the larynx within the neck, including sternothyroid, thyrohyoid, and inferior pharyngeal constrictor muscles.

Ligaments and Membranes

• Vocal ligaments: Form the core of the true vocal cords and are essential for phonation.
• Vestibular ligaments: Support the false vocal cords and contribute to airway protection.
• Thyrohyoid and cricotracheal membranes: Connect the laryngeal cartilages to adjacent structures and provide structural support.

Vascular Supply and Innervation

• Arterial supply: Superior laryngeal artery (branch of the superior thyroid artery) and inferior laryngeal artery (branch of the thyrocervical trunk) provide oxygenated blood to the larynx.
• Venous drainage: Occurs through superior, middle, and inferior laryngeal veins into the internal jugular and brachiocephalic veins.
• Lymphatic drainage: Drains primarily to deep cervical lymph nodes, important for metastasis evaluation in laryngeal cancers.
• Nerve supply: The recurrent laryngeal nerve innervates all intrinsic muscles except cricothyroid, which is supplied by the external branch of the superior laryngeal nerve. Sensory innervation is provided by both nerves to different laryngeal regions, along with autonomic fibers.

Histology of the Larynx

The larynx is lined with specialized epithelial and connective tissues that reflect its diverse functions in voice production, airway protection, and respiration.

• Epithelium: The vocal folds are covered by stratified squamous epithelium, which provides resistance to mechanical stress. Other areas of the larynx are lined with respiratory epithelium, consisting of ciliated pseudostratified columnar cells with goblet cells.
• Lamina propria and vocal fold layers: The lamina propria is composed of three layers: superficial, intermediate, and deep, which together form the vocal ligament. These layers provide elasticity and vibration capability for phonation.
• Glandular structures: Mucous and serous glands within the laryngeal mucosa keep the surface moist and facilitate smooth vocal fold vibration.

Functions of the Larynx

The larynx performs critical roles in respiration, phonation, and protection of the lower airways.

• Phonation: The vocal folds vibrate as air passes through the glottis, producing sound. Intrinsic muscles adjust tension and length of the vocal cords to modulate pitch and tone.
• Respiration: The larynx maintains airway patency, allowing unobstructed passage of air into the trachea and lungs. It also regulates airflow during activities like coughing and breath-holding.
• Protection of the lower airways: The larynx prevents aspiration of food and liquids through reflex closure during swallowing. The cough reflex is initiated when foreign material contacts laryngeal mucosa.

Clinical Examination of the Larynx

Evaluation of the larynx is essential for diagnosing structural and functional abnormalities that may affect voice, breathing, or airway protection.

• Indirect laryngoscopy: Uses a mirror placed at the back of the throat to visualize the larynx. Commonly performed in outpatient settings for initial assessment.
• Direct laryngoscopy: Provides a more detailed view of laryngeal structures using a rigid or flexible scope. Often performed under anesthesia for diagnostic or therapeutic purposes.
• Endoscopic evaluation: Flexible fiberoptic laryngoscopy allows dynamic assessment of vocal fold movement, airway patency, and mucosal lesions.
• Imaging techniques: CT, MRI, and ultrasonography can identify structural abnormalities, tumors, or trauma involving the larynx and surrounding tissues.

Common Disorders of the Larynx

The larynx is susceptible to various inflammatory, neoplastic, and structural disorders that can affect voice, breathing, and airway protection.

Inflammatory Conditions

• Laryngitis: Inflammation of the laryngeal mucosa, which may be acute or chronic, often resulting in hoarseness or loss of voice.
• Epiglottitis: Acute inflammation of the epiglottis, potentially life-threatening due to airway obstruction.

Neoplasms

• Benign tumors: Include vocal cord polyps and nodules, often related to vocal abuse or chronic irritation.
• Malignant tumors: Laryngeal carcinoma, commonly squamous cell type, can lead to voice changes, airway obstruction, and metastasis.

Structural and Functional Disorders

• Vocal cord paralysis: Results from nerve injury, affecting phonation and airway protection.
• Laryngeal stenosis: Narrowing of the laryngeal airway due to scarring, congenital anomalies, or trauma.
• Congenital anomalies: Conditions such as laryngomalacia or laryngeal webs can compromise airway patency and voice from birth.

Diagnostic and Therapeutic Interventions

Management of laryngeal disorders often requires a combination of diagnostic evaluation and therapeutic intervention tailored to the underlying condition.

• Endoscopic procedures: Used for both visualization and treatment, including biopsy of lesions or removal of small tumors.
• Microlaryngoscopy: Surgical procedure using an operating microscope to perform precise interventions on the vocal cords and laryngeal structures.
• Surgical interventions: Includes laryngectomy, cordectomy, or tracheostomy for malignant or severe structural conditions affecting the larynx.
• Voice therapy and rehabilitation: Non-surgical approach involving speech-language pathologists to restore optimal voice function and prevent further injury.

References

1. Gray H, Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd edition. London: Elsevier; 2020.
2. Shaw RJ, Slinger R, Hartley B. Laryngeal Anatomy and Physiology. In: Cummings Otolaryngology. 7th edition. Philadelphia: Elsevier; 2020.
3. Stemple JC, Glaze LE, Klaben BG. Clinical Voice Pathology: Theory and Management. 6th edition. San Diego: Plural Publishing; 2018.
4. Bhattacharyya N. Epidemiology and Clinical Aspects of Laryngeal Disorders. Otolaryngol Clin North Am. 2018;51(5):1011–1025.
5. Hirano M. Morphological Structure of the Vocal Fold. In: Vocal Fold Physiology. New York: Springer; 2016.
6. Roubeau B, Dikkers FG. Laryngeal Surgery and Voice Rehabilitation. Curr Opin Otolaryngol Head Neck Surg. 2015;23(6):429–435.
7. Gray SD, Titze IR, Chan RW. Biomechanics of Vocal Fold Function. J Voice. 2017;31(2):162–172.