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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,

  1. injury is uncommon,
  2. 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:
    • infant C3-4
    • adult: C5-6