Department of Anesthesiology - Residents Section
Anesthesia Knowledge - Anatomy
Vocal cord paralysis/Innervation of Larynx/Differences Adult-Infant
Causes for Hoarseness:
- Prolonged intubation, difficult/traumatic intubation, topical lidocain
- Unilateral injury to the recurrent laryngeal nerve (often transient)
- Bilateral injury causes stridor (bilateral paralysis of vocal cords), the vocal cords are in a paramedian position and are not moving, requires reintubation, rare complication of surgical procedures, it causes aphonia (as opposed to hoarseness in unilateral injury) indicated by inability to phonate "e".
- fiberoptic exam reveals definite diagnosis
- Hypcalcemia (24-96 hrs post surgery) can present as stridor - laryngospasm, more commonly seen after total thyroidectom
Anatomy/Innervation of larynx:
Anatomy:
- Cartilages:
- Thyroid (forms "Adam's apple)
- Cricoid
- connected by cricothyroid membrane
- arytenoids (aryepiglottic fold connects arytenoids and epiglottis)
- corniculate
- cuneiform
- corniculate and cuneiform cartilage are in close proximity to arytenoids and support it
- Muscles:
- Extrinsic muscles:
- levators
- depressors
- perform the function of swallowing
- Intrinsic muscles:
- 1 muscle controlling the laryngeal inlet
- 5 muscles controlling the movement of the vocal folds
- Blood supply:
- above VC: branch of sup. thyroid artery
- below: branch of inf. thyroid artery
Innervation:
External branch of superior laryngeal nerve: innervates cricothyroid muscle, tensor of the vocal cords, only intrinsic larynx muscle that is not innervated by the recurrent laryngeal nerve,
- injury is uncommon,
- injury will cause no apparent symptoms (its function is necessary sing high tones)
Internal branch of superior laryngeal nerve: sensory supply above the vocal cords (below: recurrent laryngeal nerve)
- both are branches of the vagus nerve as well as the recurrent laryngeal nerve
- only one muscle is able to abduct (open) the vocal cords: posterior cricoarytenoid muscle (recurrent laryngeal nerve)
Recurrent laryngeal nerve: sensory below the vocal cords; motor supply to all larynx muscles except cricothyroid muscle
Glossopharyngeal nerve: sensory: posterior third of the tongue, pharynx, carotid sinus, carotid body
- motor: stylopharyngeal muscle
- parasympathetic: parotid gland
Blockade: superior laryngeal nerve: cornu of hyoid bone
Recurrent laryngeal nerve: transtracheal injection
Differences between pediatric and adult anatomy:
- narrowest point of airway:
- adult: glottis
- infant: cricoid cartilage
- anatomical proportions:
- large floppy epiglottis
- large tongue, tonsils and adenoids
- level of larynx in the neck:
