The Larynx and Voice: Basic Anatomy and Physiology
A basic understanding of the anatomy of the larynx and the mechanics of voice production is necessary before a laryngeal disorder can be defined.
The larynx is positioned in the anterior neck, slightly below the point where the pharynx divides and gives rise to the separate respiratory and digestive tracts. Because of its location, the larynx plays a critical role in normal breathing, swallowing, and speaking. Damage to the larynx or its tissues can result in interference with any or all of these functions.
The framework of the larynx is comprised mainly of two cartilages, the upper thyroid cartilage (whose anterior prominence is oftentimes felt as the "Adam's apple"), and the lower and smaller cricoid cartilage. The epiglottis lies superiorly. This structure protects the larynx during swallowing and prevents aspiration of food.
The vocal folds lie in the center of this framework in an anterior-posterior orientation. When viewed from above the right and left folds appear as a "V"-shaped structure with the aperture between the "V" forming the entrance to the trachea. At the rear of the larynx on each side, each vocal fold is attached to a small arytenoid cartilage. Many small muscles also attach to the arytenoids. These muscles contract or relax during the various stages of breathing, swallowing, and speaking, and their action is vital to the normal function of the larynx.
Control over these muscles is provided by two branches of the vagus nerve: the recurrent laryngeal nerve and the superior laryngeal nerve. These branches are vulnerable to injury due to trauma, surgery, or other causes. If this occurs, paralysis of the vocal folds may occur. This leads to the hoarseness, aspiration, and other symptoms associated with laryngeal nerve injury.
Phonation is a complicated process in which sound is produced for speech. During phonation, the vocal folds are brought together near the center of the larynx by muscles attached to the arytenoids. As air is forced through the vocal folds, they vibrate and produce sound. By contracting or relaxing the muscles of the arytenoids, the qualities of this sound can be altered. As the sound produced by the larynx travels through the throat and mouth, it is further modified to produce speech.
Laryngitis
Laryngitis, or inflammation of the larynx, is probably the most common disorder affecting the larynx and voice. This inflammation may be of primary origin or secondary to other disorders. Laryngitis can be acute (short-term) or chronic (long-term).
Symptoms: The classic symptoms of laryngitis are hoarseness and loss of voice. Occasionally, laryngitis may cause pain in the laryngeal area during swallowing or speaking.
Causes: Laryngitis can have many causes. Acute laryngitis frequently accompanies viral or bacterial upper respiratory tract infections. Chronic laryngitis can have a number of causes. Among the most common are misuse or overuse of the voice and chronic irritation by smoke, dust, or other airborne irritants. Reflux of acid from the stomach is another frequent cause of laryngeal inflammation. Laryngitis can be secondary to a more serious condition such as benign or malignant growths. Therefore, if hoarseness lasts longer than two weeks, or is accompanied by a lump in the neck or blood-tinged sputum, medical attention should be sought.
Treatment: Acute laryngitis is treated with resting the voice as much as possible, increasing intake of decaffeinated fluids (particularly water), and using a humidifier. If a bacterial infection is the suspected cause, antibiotics may be prescribed. Chronic laryngitis is treated differently, depending on the cause. As mentioned above, if symptoms persist for longer than two weeks or if common treatments are ineffective, seek medical advice.
Nodules and Cysts
Vocal fold nodules and cysts are benign (non-cancerous) growths which can affect people of all ages. While their symptoms are similar, treatment usually differs. Cysts and nodules also differ in their location on the vocal fold. Nodules are most often bilateral and are found at the junction of the anterior and middle third of the free edge of the vocal folds. Cysts are usually unilateral and can occur anywhere on the fold. When the cyst is at the free edge, it is common for a reactive nodule to form at the same location on the other fold.
The image below is a laryngoscopic view of vocal fold nodules (yellow arrows).
Symptoms: The most common symptom of nodules and cysts is hoarseness. Voice production is often effortful. Occasionally, a growth will become large enough to cause pain.
Causes: Nodules typically occur as a result of voice misuse or overuse, which causes irritation and inflammation of the vocal fold mucosa. With continued misuse, the tissue becomes fibrotic and hardened. Cysts, on the other hand, are usually the result of a blocked mucous gland within the fold. As mucous accumulates behind the blockage, the tissue expands and a cyst is produced. There appears to be a voice misuse component to the formation of cysts, especially when they occur in the same location as nodules. Some cysts occur at the time of birth and may present with symptoms years later.
Treatment: Vocal nodules are generally treated with voice therapy. The patient is taught voice production techniques to decrease the contact force between the nodules. Voice therapy also teaches the patient to avoid behaviors which might cause or aggravate the nodules. Some medical conditions (such as allergies and laryngo-pharyngeal reflux) can maintain the presence of the nodules and require treatment. In some instances, surgery is necessary to remove the nodules. In these cases, pre- and post- operative voice therapy is also used. Cysts are treated primarily by surgical removal. Voice therapy is often useful to decrease associated swelling and improve voice quality. Therapy is also used to treat any reactive nodules.
Although recurrence is a concern, treatment for both nodules and cysts is usually successful and normal voice function returns.
Polyps
Polyps are benign lesions that occur unilaterally and usually develop at the junction of the anterior and middle third of the vocal fold edge. They may appear as pedunculated (attached by a slim stalk) or sessile (closely adhering to the mucosa). A variant of these types is the hemorrhagic polyp, which has the appearance of a blood-filled blister on the vocal fold surface.
The image below is a magnified intra-operative view of a vocal fold polyp (yellow arrow).
Symptoms: Typical symptoms of polyps include hoarseness, breathiness, or vocal roughness. These signs are commonly accompanied by the sensation of something in the throat.
Causes: Polyps are thought to result from vocal abuse and misuse. They are often associated with a single traumatic event (such as yelling at a sports event), but can be the result of prolonged vocal abuse.
Treatment: Polyps are usually surgically removed under general anesthesia. Following removal, limited voice use is recommended for a minimum of two weeks. Voice therapy is also commonly implemented to facilitate healing and minimize the potential for recurrence.
The Aging Larynx
The larynx, like any other part of the body, changes as we grow older. Many of these alterations are not noticeable; however, some of the changes can affect the quality and sound of the voice. The framework cartilages of the larynx ossify (turn to bone, which is less flexible) and the cartilages responsible for vocal fold movement become less mobile. There is often thinning of the elastin fibers in the vocal folds, thickening or fibrosis of the collagen fibers, and atrophy of the vocalis muscle. These changes interact with fatty cells replacing mucous secretors, causing a decrease in the elasticity of the vocal folds. As we age, changes to the brain and spinal cord can affect neurological control of the laryngeal muscles. The net effect is a glottal gap during voice production, decrease in fine control of the vocal folds, and vocal fold stiffness.
Perceptually, voice can become breathy, rough, hoarse, and quiet as we age. The pitch of the of the voice tends to lower for women and rise for men. With videostroboscopy, we can see aperiodic vibration, a glottic gap, and decrease in the vibratory parameters of amplitude of vibration and mucosal wave.
A program of voice therapy exercises is often beneficial in maintaining or restoring periodic vibration and improving voice quality and projection. If the glottic gap is large, there are surgical procedures available to improve vocal fold closure.
04/23/2010
Recognition/creditis given to The John Hopkins Center for Laryngeal and Voice Disorders