# Laryngeal Anatomy and the Voice Examination

## Overview
A thorough understanding of laryngeal anatomy and proficiency in laryngeal examination are foundational skills for the otolaryngologist. The layered microstructure of the vocal fold is central to understanding voice production, pathology, and surgical intervention. Modern office-based laryngoscopy with videostroboscopy is the cornerstone of voice assessment, allowing dynamic evaluation of vocal fold vibration and mucosal wave.

## Laryngeal Framework

### Cartilages
**Thyroid cartilage**: shield-shaped; largest laryngeal cartilage; oblique line laterally (attachment for strap muscles); superior and inferior cornua. **Cricoid cartilage**: complete signet ring; only complete cartilaginous ring in the airway; posterior lamina is wider; articulates with thyroid (cricothyroid joint) and arytenoid cartilages. **Epiglottis**: elastic cartilage; leaf-shaped; attached to the thyroid cartilage (thyroepiglottic ligament) and hyoid (hyoepiglottic ligament); tips posteroinferiorly during swallowing. **Arytenoid cartilages**: paired; pyramid-shaped; sit on the superior border of the cricoid lamina. Vocal process: anterior; attachment of the vocal ligament. Muscular process: lateral; attachment of posterior and lateral cricoarytenoid muscles. Apex: articulates with the corniculate cartilage. **Corniculate cartilages**: small; sit atop the arytenoid apex; within the aryepiglottic fold. **Cuneiform cartilages**: within the aryepiglottic fold; stiffen it during swallowing.

### Membranes and Ligaments
**Thyrohyoid membrane**: connects thyroid cartilage to hyoid bone; pierced by the superior laryngeal artery/vein and internal branch of the superior laryngeal nerve. **Cricothyroid membrane (conus elasticus)**: connects cricoid to thyroid cartilage; site for cricothyrotomy. **Quadrangular membrane**: from epiglottis and aryepiglottic fold to the ventricular folds (false vocal folds). **Vocal ligament**: free upper edge of the conus elasticus; forms the intermediate layer of the vocal fold.

## Vocal Fold Microstructure (Hirano's Body-Cover Model)

### Five Layers
**Epithelium**: stratified squamous; thin (0.05-0.1 mm); protects underlying tissue. **Superficial lamina propria (SLP) / Reinke space**: loose, gelatinous; critical for vibration; main surgical layer in phonomicrosurgery. **Intermediate lamina propria**: elastic fibers; contributes to vocal ligament. **Deep lamina propria**: collagen fibers; contributes to vocal ligament. **Vocalis muscle (thyroarytenoid)**: forms the body of the vocal fold.

### Functional Concept
**Cover**: epithelium + SLP (vibrates freely over the body). **Transition**: vocal ligament (intermediate + deep lamina propria). **Body**: vocalis muscle. Mucosal wave reflects the integrity of the cover-body interface. Disruption of the SLP (scar, sulcus, invasion) impairs the mucosal wave.

## Intrinsic Laryngeal Muscles

| Muscle | Action | Innervation | Function |
|--------|--------|-------------|----------|
| Posterior cricoarytenoid (PCA) | Abduction | RLN | Only abductor; opens glottis |
| Lateral cricoarytenoid (LCA) | Adduction | RLN | Closes glottis |
| Interarytenoid (IA) | Adduction | Bilateral RLN | Approximates arytenoids |
| Thyroarytenoid (TA/vocalis) | Adduction/tension | RLN | Shortens/thickens vocal fold |
| Cricothyroid (CT) | Tension | EBSLN | Lengthens/tenses vocal fold; raises pitch |

### Abductor
**Posterior cricoarytenoid (PCA)**: only abductor of the vocal folds; innervated by RLN; rotates the muscular process posteriorly, opening the glottis.

### Adductors
**Lateral cricoarytenoid (LCA)**: rotates the muscular process anteriorly, closing the glottis; RLN. **Interarytenoid (IA)**: transverse and oblique fibers; approximates the arytenoids; only muscle with bilateral RLN innervation. **Thyroarytenoid (TA/vocalis)**: shortens and thickens the vocal fold; adjusts pitch; RLN.

### Tensor
**Cricothyroid (CT)**: lengthens and tenses the vocal fold; increases pitch; innervated by the external branch of the superior laryngeal nerve (EBSLN) -- NOT the RLN.

## Innervation

### Superior Laryngeal Nerve
Branch of the vagus at the nodose ganglion. **Internal branch (IBSLN)**: sensory to supraglottis (above the vocal folds); enters through the thyrohyoid membrane. **External branch (EBSLN)**: motor to the cricothyroid muscle; runs along the superior thyroid artery (at risk during thyroid surgery). EBSLN injury: loss of high-pitched voice projection; subtle but significant for singers.

### Recurrent Laryngeal Nerve
Motor to all intrinsic muscles except the cricothyroid, Sensory to subglottis and below the vocal folds, See Topic 28 for detailed RLN anatomy.

## Laryngeal Examination

### Mirror Laryngoscopy
Indirect visualization using a laryngeal mirror and headlight. Historical gold standard; still useful for quick office assessment. Limitations: brief view, requires patient cooperation, no recording capability.

### Flexible Nasopharyngolaryngoscopy
Distal-chip or fiberoptic endoscope via the nose. Allows dynamic assessment of the airway, vocal folds, and surrounding structures. Can assess velopharyngeal closure, tongue base, supraglottis in physiologic position. Standard of care for office-based laryngeal examination. Narrow-band imaging (NBI): enhances mucosal vascular patterns; aids in detection of dysplasia and malignancy.

### Rigid Telescopic Laryngoscopy (70-degree and 90-degree)
Placed through the mouth, Superior image quality to flexible endoscopy, Best for detailed examination and documentation. Limitation: tongue protrusion and phonation required; cannot assess dynamic swallowing.

### Videostroboscopy
Stroboscopic light source synchronized to the fundamental frequency of voice. Creates an apparent slow-motion image of vocal fold vibration. Assesses: **Mucosal wave**: traveling wave on the vocal fold surface; reflects SLP integrity. **Amplitude**: lateral excursion of the vocal fold edge. **Symmetry**: phase and amplitude symmetry between the two vocal folds. **Periodicity**: regularity of the vibratory cycle. **Glottic closure pattern**: complete, incomplete, hourglass, posterior gap, anterior gap, spindle. **Non-vibrating segments**: suggest scar, sulcus, or submucosal lesion. Essential for differentiating benign from malignant lesions, assessing vocal fold pliability, and surgical planning.

### High-Speed Videoendoscopy
Records actual vocal fold vibration at >2000 frames per second. Does not rely on stroboscopic illusion; captures aperiodic vibration (cannot be assessed with stroboscopy). Research and specialized clinical applications; not yet routine.

## Voice Assessment

### Perceptual Assessment
**GRBAS scale**: Grade, Roughness, Breathiness, Asthenia, Strain (0-3 each). **CAPE-V**: Consensus Auditory-Perceptual Evaluation of Voice; visual analog scales for overall severity, roughness, breathiness, strain, pitch, loudness.

### Acoustic Analysis
Fundamental frequency (F0): average pitch; male ~120 Hz, female ~220 Hz. Jitter: cycle-to-cycle variation in frequency (normal <1%). Shimmer: cycle-to-cycle variation in amplitude (normal <3%). Harmonics-to-noise ratio (HNR): signal quality; higher is better. Maximum phonation time (MPT): normal >15 seconds; reduced with glottic insufficiency.

### Aerodynamic Assessment
Subglottic pressure estimation (using /pi/ repetition), Phonation threshold pressure. Airflow rate: elevated with glottic gap; reduced with hyperfunctional voice.

### Patient-Reported Outcomes
Voice Handicap Index (VHI-10 or VHI-30), Voice-Related Quality of Life (V-RQOL). Reflux Symptom Index (RSI) if laryngopharyngeal reflux suspected.

<image>Cross-sectional diagram of the vocal fold showing Hirano's five-layer microstructure. From superficial to deep: stratified squamous epithelium (thin), superficial lamina propria (Reinke space, shown as loose gelatinous layer), intermediate lamina propria (elastic fibers), deep lamina propria (collagen fibers), and vocalis muscle (thyroarytenoid). The body-cover model is labeled alongside: cover (epithelium + SLP), transition (vocal ligament = intermediate + deep LP), and body (muscle). An adjacent coronal section of the larynx shows the true vocal folds, ventricle, and false vocal folds with their respective layers.</image>

<image>Intrinsic muscles of the larynx shown in posterior and superior views. Posterior view shows the posterior cricoarytenoid muscles (with arrows indicating abduction), interarytenoid muscles (transverse and oblique fibers), and the cricothyroid muscle from the lateral view. Superior view looking down into the larynx shows the lateral cricoarytenoid and thyroarytenoid muscles with arrows demonstrating their actions on the arytenoid cartilages. Each muscle is color-coded with its innervation listed (RLN vs. EBSLN). A small inset diagram shows the arytenoid cartilage with the vocal process and muscular process labeled to illustrate the rotational mechanics of abduction and adduction.</image>

<image>Videostroboscopy findings comparison chart. Six panels showing still frames from stroboscopy during different phases of vibration. Panel A: Normal mucosal wave with symmetric, periodic vibration and complete glottic closure. Panel B: Vocal fold polyp with asymmetric vibration and disrupted mucosal wave over the lesion. Panel C: Vocal fold paralysis with incomplete glottic closure and absent vibration on the paralyzed side. Panel D: Vocal fold scar with absent mucosal wave and stiff segment. Panel E: Reinke edema showing polypoid change with exaggerated mucosal wave. Panel F: Early glottic carcinoma with absent mucosal wave and irregular vascular pattern on narrow-band imaging inset.</image>

## Clinical Pearls
The superficial lamina propria (Reinke space) is the critical vibrating layer of the vocal fold; preservation of this layer during phonomicrosurgery is essential for voice outcomes. The cricothyroid muscle is the only intrinsic laryngeal muscle innervated by the external branch of the SLN, not the RLN; its injury causes loss of voice projection and high-pitch capability. Stroboscopy is essential for differentiating benign vocal fold lesions from malignancy; an absent or disrupted mucosal wave over a lesion raises concern for invasion into or through the SLP. Glottic closure pattern on stroboscopy directly informs treatment planning: posterior gap suggests muscular tension dysphonia; spindle gap suggests bilateral vocal fold atrophy; incomplete closure on one side suggests paresis or paralysis. Always perform perceptual voice assessment (GRBAS or CAPE-V) and collect patient-reported outcomes (VHI) alongside instrumental examination; the combination provides a comprehensive voice profile. Narrow-band imaging during laryngoscopy enhances vascular patterns and improves detection of early mucosal neoplasia compared to white light alone.

## References
- Hirano M. "Morphological structure of the vocal cord as a vibrator and its variations." *Folia Phoniatr*. 1974;26(2):89-94.
- Rosen CA, Lee AS, Osborne J, Zullo T, Murry T. "Development and validation of the Voice Handicap Index-10." *Laryngoscope*. 2004;114(9):1549-1556.
- Patel RR, Awan SN, Barkmeier-Kraemer J, et al. "Recommended Protocols for Instrumental Assessment of Voice." *Am J Speech Lang Pathol*. 2018;27(3):887-905.
- Arens C, Piazza C, Andrea M, et al. "Proposal for a descriptive guideline of vascular changes in lesions of the vocal folds by the committee on endoscopic laryngeal imaging of the European Laryngological Society." *Eur Arch Otorhinolaryngol*. 2016;273(5):1207-1214.