A. Anatomy and physiology
- The larynx is divided into the supraglottis (which includes the epiglottis, arytenoid cartilages, false vocal folds, and ventricle), the glottis (true vocal folds), and subglottis (from the true vocal folds to the cricoid cartilage). The thyroid and cricoid cartilages and the hyoid bone provide the rigid support for the larynx
- The superior laryngeal nerve provides sensory innervation to the supraglottic mucosa and motor innervation to the cricothyroid muscle. The recurrent laryngeal nerve provides sensory innervation to the remaining laryngeal mucosa and motor innervation to all the intrinsic laryngeal muscles. Both are derived from the vagus nerve (CN X).
- The larynx is a critical part of the aerodigestive tract. It contributes to airway protection, deglutition, and phonation. Laryngeal elevation, glottic closure, and retroflexion of the epiglottis help to prevent aspiration during swallowing. Coughing consists in increasing subglottic pressure by contracting expiratory muscles against a tightly closed glottis. The larynx suddenly opens, resulting in a rapid outflow of air and expulsion of mucus or foreign materials from the airway.
B. Congenital disorders
- Laryngomalacia is the most common congenital laryngeal abnormality. An omega-shaped epiglottis and floppy arytenoid towers prolapse into the airway on inspiration, creating inspiratory stridor. Symptoms generally worsen for the first 18 months of life and then improve. If respiratory or feeding difficulties result in failure to thrive, endoscopic supraglottoplasty is recommended.
- The second-most-common laryngeal abnormality in the newborn is vocal cord paralysis. These are often idiopathic but may be related to central nervous system (CNS) malformations such as the Arnold-Chiari malformation. Most cases resolve spontaneously. Bilateral vocal cord paralysis often requires tracheostomy.
- Other congenital laryngeal abnormalities include laryngeal atresia, webs, cysts, laryngeal clefts, and subglottic stenosis. Subglottic stenosis can be either congenital or acquired. Surgical laryngotracheal reconstruction or cricotracheal resection is often necessary.
- Blunt or penetrating laryngeal trauma requires rapid airway assessment and control, possibly requiring intubation or tracheostomy. Diagnostic modalities include fiberoptic laryngoscopy, high-resolution CT scan, and operative endoscopy. Laryngeal hematomas and small lacerations are managed conservatively with airway observation and humidified air. Displaced fractures and laryngeal instability require urgent tracheostomy followed by open reduction and internal fixation.
- Caustic ingestions can be classified by the type of material ingested. Alkali ingestions result in liquefactive necrosis of the laryngeal suprastructure, pharynx, and esophagus and put the patient at risk for stenosis. Acidic materials cause coagulative necrosis. Endoscopy is recommended 24 to 48 hours after ingestion. Initial therapy includes nasogastric (NG) tube placement and high-dose systemic steroids. If strictures occur, they are assessed with barium swallow studies and may require periodic esophageal dilation.
D. Infectious/inflammatory disorders
- Viral croup, or viral laryngotracheitis, occurs mostly in children and is an inflammation of the glottis and subglottis caused mainly by parainfluenza viruses 1 and 2. Viral croup is diagnosed clinically, often with a history of a prodromal upper respiratory infection followed by stridor and a barking cough. Treatment of most cases is supportive; however, severe cases respond well to glucocorticoids.
- Epiglottitis is a medical emergency. Children with epiglottitis present acutely (within 2 to 6 hours) with a high fever, drooling, and sitting upright with inspiratory stridor. Airway management is the preeminent concern. In a study, most cases of epiglottitis required intubation (Laryngoscope 1994;104:1314). Administration of antibiotics is the main treatment. Widespread vaccination against H. influenzae type B has significantly decreased its incidence; however, emerging reports of epiglottitis in fully vaccinated children underscore the importance of clinicians quickly recognizing this disease entity (Int J Pediatr Otorhinolaryngol 2003;67:317).
- Acute laryngitis is an inflammation of the laryngeal mucosa and vocal cords resulting in hoarseness. Most cases occur in adults and are of viral origin. Acute laryngitis is usually self-limited and requires strict voice rest.
- Laryngopharyngeal reflux refers to the retrograde movement of gastric contents into the larynx/hypopharynx and is characterized by cervical dysphagia, globus, sore throat, cough, hoarseness, and chronic throat clearing. It is believed to be an esophageal sphincter disorder and is treated with diet, behavior modifications, and high-dose proton-pump inhibitors (Allergy Asthma Proc 2006;27:21).
- Other inflammatory lesions that affect the larynx include sulcus vocalis, contact ulcers, vocal nodules, granulomas, and smoker’s laryngitis.
E. Neuromuscular disorders
a.Chronic aspiration is caused by a loss of the protective functions of the larynx due to impaired motor activity or sensory loss. Aspiration can result in bronchopulmonary infection and airway obstruction.
- Causes of chronic aspiration include cerebral damage (stroke, tumor, trauma), degenerative neurologic diseases (Parkinson disease, amyotrophic lateral sclerosis, multiple sclerosis), neuromuscular disorders (myasthenia gravis, muscular dystrophies), and surgical alteration of the larynx (following cancer resection).
- Treatment of chronic aspiration first requires elucidation of the dysfunction by performing swallowing studies. Focused physical therapy with a speech/swallowing therapist corrects many cases. Refractory cases can be treated with nasogastric, gastric, or parenteral nutrition. Surgical treatments include tracheostomy, vocal cord medialization, and laryngectomy.
b.Vocal cord paralysis occurs when the recurrent laryngeal nerve (RLN) is damaged. Due to the lengthy path of the RLN from the vagus nerve down into the thorax and back up to the larynx, the RLN can easily be damaged by surgery, neoplasm, or trauma to the thorax or neck. Recognized iatrogenic injuries should be repaired by primary epineural anastomosis or cable grafting. Patients presenting with a new diagnosis of vocal cord paralysis require a CT scan and/or MRI of the neck and chest to rule out other pathologies. Unilateral vocal cord paralysis puts patients at risk for aspiration and greatly affects phonation. Treatment consists of speech therapy and observation. Partial to full recovery often occurs over many months. Surgical options include injection laryngoplasty (with Gelfoam, fat, or Cymetra), medialization of the vocal cord, and laryngeal reinnervation. Bilateral vocal cord paralysis often results in airway obstruction and is treated with arytenoidectomy, cordectomy, or tracheostomy.
c.Spasmodic dysphonia (laryngeal dystonia) is laryngeal motion disorder. The pathophysiology of spasmodic dysphonia is unknown. It is effectively treated with botulinum toxin injections into the laryngeal musculature.