The Anatomy Of The Larynx And Its Role In Phonation Essay
Why are hoarseness and change to the pitch of the voice possible complications of thyroid surgery?
Complications of thyroid surgery resulting in hoarseness and changes to the pitch of the voice are a result of injury to the laryngeal nerves. Laryngeal nerve damage can have an adverse effect on the muscles that move the vocal folds (cords), hence affecting the quality of voice. Although incidence of nerve injury during thyroid operations has decreased over the last two decades(*), appropriate precautions are routinely implemented during thyroid surgery, to minimise nerve damage. The thyroid vessels are closely associated with the laryngeal nerves. Therefore, an important consideration in achieving successful thyroid surgery is the detailed understanding of the anatomy and physiology (*) of the larynx and thyroid, coupled with the surgical approach itself.
Anatomy of the larynx and its role in phonation
The larynx is a highly intricate organ (Figure 1) which consists of a network of cartilage, intrinsic and extrinsic muscles, and connective tissue.The Anatomy Of The Larynx And Its Role In Phonation Essay. It is situated in the anterior side of the neck in line with the third and sixth cervical vertebrae1. The cartilages found in the laryngeal wall are the single thyroid, epiglottis and cricoid cartilages, of which the thyroid is the largest cartilage; and the paired arytenoid, cuneiform and corniculate cartilages. The arytenoid cartilages have vocal process to provide the sites of attachment for the vocal ligament, thereby permitting opening and closing movement of the vocal folds in phonation. Thus the larynx plays an important role in phonation in speech.
The vocal folds (true vocal cords) are the wedge-shaped structures that protrude from the lateral surfaces of the larynx, creating a narrow aperture across their air passage known as the rima glottidis. Sound is produced when the adductor muscles such as the cricoarytenoid muscle contract. The vocal folds are then brought closer together which closes the rima glottidis thereby providing high resistance to exhaled air from the lungs. Air is then forced through the bottom edge of the vocal cord followed by the upper edge. As air passes through the vocal folds the air pressure decreases producing a Bernouli Effect* which causes the lower edge to close followed by the upper edge and finally closing the vocal folds back together. Closure of the vocal folds produces smooth, regular vibrations that create sound. Sound is then converted to voice by vocal tract resonators which shape the sound to produce various resonances.
Changes to the pitch of voice depend on the degree of tension and length of the vocal folds. Alterations to pitch are largely due to actions of intrinsic laryngeal muscles, namely the cricothyroid muscle. The cricothyroid muscle stretches the vocal ligaments by raising the arch of the cricoid cartilage and tilting the lamina backwards (*) and thereby increasing the tension and length of the vocal folds (*). Therefore, contraction of the cricothyroid muscle abducts the vocal folds so that when they vibrate, high pitched sound is produced.
By contrast, production of lower pitch sounds require the vocal folds to adduct, narrowing the rima glottidis and thus decreasing vocal fold muscular tension. The Anatomy Of The Larynx And Its Role In Phonation Essay.
Nerve supply to the larynx – relations to thyroid gland
Below the larynx lies the thyroid gland which is one of the larger endocrine glands with an abundant vascular system. The thyroid gland descends to the anterior region of the neck located deep to the sternothyroid and sternohyoid muscles from the level of C5-T1 (*). It consists of two lateral lobes connected by the isthmus that lie on the left and right side of the trachea. There may also be a small pyramidal lobe which has its superior end ascending from the isthmus towards the oblique line. A thin fibrous capsule encompasses the thyroid gland which expands into deeper parenchyma (*) of the gland. The capsule combines with the cricoid cartilage by dense connective tissue forming the suspensory ligament of Berry. Once the ligament of Berry is formed, the RLN can gain access into the larynx (*).
Innervation of the larynx is important in the transmission of nerve impulses to and from the brain. The vagus nerve innervates the larynx via the external and internal laryngeal nerves, which are collectively terminal branches of the superior laryngeal nerve (SLN), and via the recurrent laryngeal nerve (RLN). Most intrinsic laryngeal muscles are innervated by the RLN except for cricothyroid muscle which is supplied by the external LN.
The external LN descends on the outer fascia of the inferior pharyngeal constrictor muscle (*) in close association with the superior thyroid artery. The external LN can in rare occasions (*) run beneath the sternothyroid muscle, in its course, towards the oblique line of the thyroid cartilage to innervate the cricothyroid muscle. Interestingly, the connection of the artery and nerve is highly variable and new variations have been documented(*): for example, Type 1 anatomy shows the nerve crosses the superior thyroid vessels equal to, or greater than one centimetre superior to the thyroid pole. The internal LN provides sensory fibres to the larynx and the laryngopharynx after penetrating the thyrohyoid membrane. The internal LN further divides into the superior, middle and inferior branches before entering the larynx.
The RLN has close contact posterior laterally (*) with the lateral lobes of the thyroid gland. It is termed recurrent because it retrogrades in the chest and continues superiorly back into the neck (*). A close association exists between the superior region of the RLN and the inferior thyroid artery. Like the SLN and the superior artery, this relationship is highly variable. The RLN can be found anterior, posterior, or through the branches of the inferior thyroid artery. The course of the left and right recurrent laryngeal nerves of the RLN reaches the larynx through slightly different routes. The right recurrent LN reaches the larynx after looping around the right subclavian artery and ascending at an oblique angle in the tracheosophageal groove (*).The Anatomy Of The Larynx And Its Role In Phonation Essay. The nerve pierces the inferior constrictor muscle of the pharynx before entering the larynx. The left RLN route differs by looping posteriorly around the aortic arch, but like the right RLN, it ascends in the tracheosophageal groove (*) until reaches the larynx via the inferior constrictor muscle. The two main divisions of the RLN are the anterior and posterior branches. The anterior branch supplies motor fibres to all the intrinsic laryngeal muscles with the exception of cricothyroid( which is supplied by the external LN). The posterior branch is predominantly sensory and transports the sensory fibres from the larynx and laryngopharynx(*).
Injury to laryngeal nerves during thyroid surgery
The laryngeal nerves carry a high risk for injury during thyroid surgery which manifests voice problems such as changes in pitch and hoarseness. It is well documented that thyroidectomy is the most common cause of injury to the external LN (*). The close relationship that exists between the external LN and the superior thyroid artery predisposes the external LN to injury when the artery is clamped during thyroid surgery. Injury to the external LN results in paralysis of the cricothyroid muscle, coordinator of the vocal folds. Patients with external LN damage lose the ability to forcefully project their voice and additionally lose their upper voice register. This is due to loss of function of the cricothyroid muscle to alter the tension of the vocal folds. Occasionally, the voice becomes monotonous in character. The effects of injury to the external LN are generally subtle and unnoticeable in patients except for those whose careers largely depend on the use of their normal voice such as professional singers and orators(*). Voice function returns to normal after a few months after surgery unless injury to the external LN is permanent.
Recurrent laryngeal nerve injury is still of major concern in thyroid surgery, as it is the most frequent post-thyroidectomy complication (*). Injury to the RLN frequently results from common surgical techniques such as suturing, crushing and ligating the nerve and its neighbouring branches. The clamping of the RLN together with the inferior thyroid artery during surgery can severely damage the RLN due to the close proximity of the RLN to the inferior thyroid artery. Seeing as the main functions of the RLN is to innervate the laryngeal muscles and permit abduction and adduction of the vocal folds, injury of the nerve results in paralysis of the vocal fold.The Anatomy Of The Larynx And Its Role In Phonation Essay. In unilateral RLN paralysis, where for example the RLN is completely transacted (*), the voice immediately becomes hoarse because the paralysed vocal fold assumes a paramedian position. The lack of nerve supply results in cord flaccidty in which the paralysed vocal fold gradually atrophies. In addition, the vocal fold is unable to adduct for phonation, and abduct for deep breathing causing inadequate closure of the rima glottidis. Therefore, air will escape during phonation thereby leading to dysphonia (hoarseness). Dysphonia may either stay permanent or decline over time (*).Bilateral lesion of the RLN, however, has more serious complications. The patient with bilateral paralysis have both vocal cords in a paramedian position (*) and cannot be abducted upon inspiration leading to airway obstruction. As a result the patient exhibits biphasic stridor (*) which causes a high-pitched voice and noisy breathing. In the rare occasions the vocal fold will remain permanently paralysed after thyroid surgery and patients may experience a complete loss of voice.
Possible techniques to minimise nerve damage
Preventing inadvertent injury to the SLN and RLN is crucial in achieving successful thyroid operations which maintains the patient’s quality of voice. Intraoperative neuromonitoring of the laryngeal nerves is a way of identifying and monitoring the course of the RLN and SLN and thus, preventing its iatrogenic injury during surgery. Patients with unilateral paralysis of the RLN can undergo ansa-RLN reinnervation. Reinnervation restores tone and bulk to the intrinsic laryngeal muscles and hence restores a relatively normal voice,without interfering with the vocal fold function or structure.
The laryngeal nerves are branches of the vagus nerve. With the exception of the cricothryoid muscle, the RLN innervates the laryngeal muscles which coordinate the vocal folds for phonation. Evidently, the relationship between the RLN and the SLN and the laryngeal muscles are of great importance because damage to the laryngeal nerves result in changes in voice quality. The close relationship between the thyroid vessels and the laryngeal nerves is a primary reason why meticulous techniques are essential in thyroid surgery, to minimise injury to the laryngeal nerves and prevent voice complications. Surgical management of the complications in thyroid surgery have recently experienced great improvements(*) which safely restore the patient’s normal voice improving their everday life.
Fig.1 Anterior and posterior view of the larynx6
Fig2. (Left) anterior view of thyroid gland
The larynx splits into three distinct regions known as the supraglottis, glottis, and subglottis. Within these three regions the cartilage, neurovascular, and musculature are all intertwined to allow the larynx to function as a unit and carry out its many functions.The Anatomy Of The Larynx And Its Role In Phonation Essay. The primary functions of the larynx are voice production, protection of the airway during respiration, and swallowing.
The article reviews the most current scientific knowledge on the anatomy and function of the laryngeal-vocal cords system, integrating with the clinic, embryology, and related conditions.
The larynx relies on cartilaginous support for its flexible, yet stable structure. The cartilages separate into two groupings. The first set of cartilages are considered to be unpaired cartilages of the larynx (known as the thyroid and cricoid cartilages). Two laminae of the thyroid cartilage come together to join anteriorly at the laryngeal prominence, popularly known as the “Adam’s apple”. Posteriorly, the two laminae of the thyroid cartilage remain open. The posterior aspect of each thyroid cartilage lamina extends superiorly and inferiorly forming both the superior and inferior horns. The superior horn of the thyroid cartilage makes an attachment to the hyoid bone via the thyrohyoid membrane and the lateral thyrohyoid ligament. Within this thyrohyoid membrane lies a foramen in which both the superior laryngeal vessels and the internal branch of the superior laryngeal nerve reside. The lateral thyrohyoid ligament may contain triticeous cartilage that is often mistaken for a foreign body when it calcifies. The inferior horn attaches to the cricoid cartilage via the cricothyroid membrane.
The cricoid cartilage is the only full cartilage ring within the larynx. It is composed of hyaline cartilage and often referred to as having a “signet ring” appearance. The posterior aspect of the cricoid cartilage, known as the lamina, is much wider than the anterior portion of the cartilage, referred to as the arch of the cricoid. The wider posterior portion serves as a base for the arytenoid cartilages to articulate via a ball and socket joint. Each arytenoid cartilage has two important processes that extend from it. The first being the vocal process responsible for serving as an attachment for the vocal ligament.The Anatomy Of The Larynx And Its Role In Phonation Essay. The second process is the muscular process and serves as an attachment for intrinsic laryngeal muscles. These two processes, combined with the unique ball and socket articulation with the cricoid, allow the arytenoid to rotate within the facet causing adduction or abduction of the vocal ligament and vocal folds required for airway protection and phonation.
The second set of cartilages (arytenoid, cuneiform, and corniculate cartilages), are known as paired cartilages and lie internally within the larynx. The cuneiform and corniculate cartilages are fibroelastic cartilages and mainly function to provide rigidity to the aryepiglottic folds. The corniculate lies above and sits on the arytenoid cartilage, while the cuneiform lies within the aryepiglottic folds.
Ventricle, Folds, and Membranes
The vocal folds are now widely agreed upon and understood facets of voice because of modern histological techniques. The vocal fold comprises five layers (deep to superficial layers as follows): thyroarytenoid muscle, deep lamina propria, intermediate lamina propria, superficial lamina propria, and the squamous epithelium. The deep and intermediate lamina propria both are grouped to form the vocal ligament mentioned above. The superficial layer of the lamina propria provides a gelatinous surface upon which the vocal folds to vibrate.
The opening into the laryngeal lumen is lined by the aryepiglottic folds in which several of the cartilages lie (including the cuneiform, corniculate, and arytenoid cartilages). A common location for food to get lodged is known as the piriform sinus, and it can be found bilaterally surrounding the aryepiglottic folds.
The laryngeal ventricle is both an outpouching the laryngeal wall and potential space. It lies between the supraglottic and glottic larynx. It extends laterally as an outpouching that is known as the laryngeal saccule because of its ability to collapse upon itself. This saccule becomes important in the clinical context of saccular cysts which will be discussed further at another time. It is difficult to asses the laryngeal ventricle in its entirety when examining the patient via nasopharyngeal endoscopy; therefore, it must be in the mind of the clinician when ruling out cancer and to monitor the progression of malignancy.
Two structures within the larynx are important to prevent the spread of malignancy. The first is the quadrangular membrane. It houses the ventricular ligament. The other structure is the conus elasticus. This membrane spreads from the cricoid cartilage to the vocal ligament within the true vocal folds. The Anatomy Of The Larynx And Its Role In Phonation Essay.
The musculature will be discussed in detail further below in the text. However, it is important to mention how the muscles of the larynx function in phonation, swallowing, and respiration. During respiration, air flows best during abduction of the vocal folds. Therefore, it is reasonable to state that the posterior cricothyroid is solely responsible for optimal respiration. Regarding phonation, adducted vocal folds produce the best sound quality. The adductors of the vocal folds, and thus those providing optimal sound quality, are the thyroarytenoid, interarytenoid, and the lateral cricoarytenoid muscles. Higher pitched phonation, however, is best when the vocal folds tense via the two bundles of the cricothyroid muscle. The pars recta, the vertically oriented bundle, attaches to the anterior portion of the cricoid and the thyroid cartilage thus causing an anterior rotation around the cricothyroid joint when it contracts. The second bundle is oriented upward and backward and is known as the pars oblique. The pars oblique contracts and subsequently displaces its attachments at the anterior surfaces of the cricoid cartilage and thyroid cartilage posteriorly. These two actions together cause increased tension and elongation of the vocal folds. The Anatomy Of The Larynx And Its Role In Phonation Essay.
The larynx develops during the fourth week of development from both the endoderm and the mesoderm. The internal lining of the larynx originates from the endoderm while the cartilages and muscles develop from the third, fourth, and sixth pharyngeal arches. At the fourth week, an outgrowth known as the laryngotracheal groove appears from the developing foregut. This groove deepens and eventually forms the esophagotracheal septum, allowing the esophagus to lie on the dorsal side of the septum and the rest of the respiratory tract anteriorly. The groove’s length continues to become the laryngotracheal diverticulum which eventually will give rise to the larynx, trachea, and lungs. The laryngeal lumen at first is obliterated due to the epithelial proliferation. However, it becomes re-canalized between weeks 7 to 10. The arches give rise to the nerves, cartilages, and musculature in the larynx. They are:
Third Branchial Arch
Fourth Branchial Arch
Sixth Branchial Arch
Interestingly, no part of the larynx is ossified at birth. The first to ossify is the hyoid around the second or third year of life. The teenage years are when the thyroid cartilage ossifies, while the cricoid does not ossify until the fourth decade of life. The Anatomy Of The Larynx And Its Role In Phonation Essay.
The blood supply to the larynx comes from two large vessels: the external carotid artery and the subclavian artery. The external carotid artery gives off the superior thyroid artery as the first branch within the neck. From the subclavian artery originates the thyrocervical trunk, which then gives rise to the inferior thyroid artery. Each artery gives off pharyngeal arteries, which supply the larynx.
The superior and middle thyroid veins both drain into the internal jugular vein. The inferior thyroid vein drains directly into the subclavian vein. Meanwhile, lymph drainage goes to the deep cervical, paratracheal, pre-tracheal, and pre-laryngeal nodes. Interestingly, the recurrent laryngeal node is the most common site of metastasis of esophageal squamous cell carcinoma.
The primary innervation to the vocal folds comes from branches of the vagus nerve, which are the superior and inferior laryngeal nerves. The superior laryngeal nerve splits into the external laryngeal nerve and the internal laryngeal nerve approximately at the level of the greater horn of the hyoid. The internal laryngeal nerve travels through the thyrohyoid membrane with the superior laryngeal artery. The internal branch of the superior laryngeal nerve supplies all sensation to mucosa above the vocal folds, and it can be accessed rather easily from beneath the medial wall of the piriform fossa for anesthesia. The external laryngeal nerve is the source of motor innervation to the cricothyroid muscle. Its location is usually close to the superior thyroid artery as well as the superior pole of the thyroid. The several variations of its location are discussed below.
The inferior laryngeal nerve is better known as the recurrent laryngeal nerve, and it supplies all motor and sensory innervation below the vocal folds. The Anatomy Of The Larynx And Its Role In Phonation Essay. It is known as the recurrent laryngeal nerve due to its unique course underneath the arch of the aorta on the left and underneath the subclavian artery on the right. After coursing underneath each vessel on the corresponding side, the nerve courses superiorly with the inferior thyroid artery. It eventually passes deep to the inferior constrictor muscles and enters the larynx posterior to the cricothyroid articulation. Later in this article, there is a discussion of several landmarks to help identify this nerve in surgery.
The musculature of the larynx and surrounding structures separate into two distinct categories. The first being the external musculature that is then broken down into either depressors or elevators of the larynx based on their action. The depressors of the larynx are the sternohyoid, sternothyroid, omohyoid, and are collectively known as the “strap”, or “infrahyoid”, muscles. This group of muscles receives innervation from C1-C3. The elevators of the larynx are the geniohyoid, digastric, thyrohyoid, mylohyoid, and stylohyoid muscles. These are collectively known as the “suprahyoid muscles”. Innervation to these muscles is more complex than the strap muscles, with innervation coming from C1, CN V3, and CN VII. The primary function of the external musculature is swallowing. The final group of external laryngeal muscles consists of the superior, middle, and inferior constrictors. These are all innervated by the pharyngeal plexus and primarily function to propel the food bolus distally.
Internal musculature is the primary group of muscles involved in phonation by either abducting or adducting the vocal folds. The sole abductor of the group is the posterior cricoarytenoid. The muscles, lateral cricoarytenoid, thyroarytenoid, interarytenoid, and cricothyroid, all act together to adduct the vocal folds. All the internal muscles of the larynx receive nerve supply from the recurrent laryngeal nerve with the exception of the cricothyroid, which is innervated by the external branch of the superior laryngeal nerve. The Anatomy Of The Larynx And Its Role In Phonation Essay.
The exact mechanism by which the muscles function to swallow, produce voice and aid in respiration has been covered above.
Several variations to the location to the recurrent laryngeal nerve (RLN) have been identified and will be discussed here. Chiang et al. describe variations such as extra-laryngeal branches, distorted RLN, intertwining branches of RLN between the Inferior Thyroid Artery, and non-recurrent laryngeal nerves. Recognition of these variations is essential to avoid iatrogenic injury to the RLN during thyroid surgery. Extra-laryngeal branches have been reported to be present in 40-60% of patients. The most common location for extra-laryngeal branches of the RLN is at the ligament of Berry, in which both an anterior and posterior branch is seen. Distorted RLN is most often found in those patients with recurrent goiters or those presenting with a large goiter. Due to the size of these goiters, the RLN may be stretched or even pass through the capsule of the goiter increasing the risk of iatrogenic injury. An article by Tang et al. studied the different variations between the inferior thyroid artery (ITA) and the RLN. They found that the RLN varies in its position bilaterally with the inferior thyroid artery. On the left, the RLN was found to be posterior to the ITA in 86.25% of cases. In less than 10% of cases, it was seen anteriorly of the ITA and found to be intertwined within the branches of the ITA in 3% of cases. On the right, the RLN was found to be anterior to the ITA 75% of the time. The Anatomy Of The Larynx And Its Role In Phonation Essay.In less than 10% of cases, is located posteriorly to the artery, while only 5% of cases it was found intertwined within the branches of the ITA. A non-recurrent laryngeal nerve is much rarer than the other variations discussed above. It has never been reported on the left side on its own without other significant pathology and only been found to be present in 0.7% of patients on the right side according to a meta-analysis done by Henry et al.
The most common etiology of iatrogenic injury to the recurrent laryngeal nerve is during thyroidectomy, with a discussion of the consequences below. Therefore, surgeons must rely heavily on landmarks intraoperatively to identify and save the recurrent laryngeal nerve. Several landmarks are used intraoperatively, including the tracheoesophageal groove (TEG), tubercle of Zuckerkandl (ZT), ligament of Berry (BL), and the inferior thyroid artery (ITA). The ligament of Berry serves to connect the thyroid to the first three rings of tracheal cartilage. Studies have shown that the BL is the most reliable landmark because 78.2% of the time it coursed superficially to the RLN. The next most reliable landmark to identify the recurrent laryngeal nerve is the tracheoesophageal groove. Here, it is found to lie within the TEG 63.7% of the time.
Recurrent Respiratory Papillomatosis (RRP) is a benign laryngeal neoplasm seen in 4 per 100,000 children and 2 per 100,000 adults. The bimodal distribution of RRP subsequently categorizes the disease into both a juvenile type (presenting before age 12) and an adult type (presenting after age 12). In children, acquisition of the infection is most commonly through the vaginal canal via infected secretions from anogenital warts. In contrast, adults most often come into contact with the infection through oral sex. Regardless of the transmission, the causative virus is HPV of the papillomaviridae family. Types 6, 11, 16, 18, 31, and 33 can all cause RRP. Types 6 and 11 account for greater than 90% of cases. The presenting symptoms of RRP are dysphonia, stridor, and dyspnea. The more aggressive symptoms of RRP most commonly occur with HPV type 11. The feared complication of RRP is the involvement of the respiratory tract leading to bouts of pneumonia, atelectasis, and even hemoptysis mimicking tuberculosis. To further diagnose patients with these symptoms, chest x-rays may be performed to identify respiratory tract involvement. RRP may show up as many solid and cavitated nodules. Therefore, the utility of chest X-rays is limited. The standard imaging modality to identify these nodules within the respiratory tract is helical CT. The Anatomy Of The Larynx And Its Role In Phonation Essay.CT findings of pulmonary RRP includes multiple centrilobular lesions that may become cystic with air-fluid levels if they become infected. They are most common in the posterior and basal regions of the lung. To date, there is no complete and curative treatment for RRP. The best mode of treatment is resection of as much of the exophytic papilloma as possible while restoring normal function of the larynx. Attempted adjuvant therapy with cidofovir has been unsuccessful.
Chondromas of the larynx and granular cell tumor are two other benign neoplasms that may affect the vocal folds. Chondromas are rare neoplasms most commonly found in men that most often arise from the lamina of the cricoid. Over 85% of chondromas occur on the cricoid, thyroid or arytenoid cartilages. As discussed above, the musculature used in phonation attaches to all three cartilages. Due to the location and relationship with intra-laryngeal musculature, hoarseness is the most common complaint observed in patients presenting with chondromas. Depending on the site of the chondroma, patients may also present with dyspnea and dysphagia. Diagnosis of chondromas is usually accomplished by wedge biopsy and CT of the neck to see the extent of the chondroma. Treatment is complete resection. Granular cell tumors go by different names including granular cell myoblastomas and Abrikossoff tumors. These tumors most likely originate from Schwann cells, and only about 10% arise in the larynx. When found in the larynx, granular cell tumors occur either on the true vocal fold or arytenoids. These tumors may sometimes be confused with squamous cell carcinoma due to pseudo-epitheliomatous hyperplasia visualized histologically. Cytoplasmic eosinophilic granules that stain PAS positive are also a possibility. These tumors are also S-100 positive. Most patients present with acute hoarseness of sudden onset. Treatment is by complete resection.
Reinke’s Edema (Polypoid Corditis)
The superficial lamina propria is also known as Reinke’s Space, and it is composed of loose connective tissue. Due to the makeup of Reinke’s space, it is susceptible to fluid accumulation due to chronic irritation and inflammation secondary to smoking. Irritation and inflammation eventually lead to the formation of polyps on vocal folds contributing to difficulty in the inherent vibration seen during phonation. The Anatomy Of The Larynx And Its Role In Phonation Essay.Thus, patients will present with altered voice, more commonly a deeper voice. Women will often present complaining they sound like a man. The mainstay of treatment is first to treat the underlying disease that led to polypoid corditis such as hypothyroidism, vocal abuse, laryngopharyngeal reflux or smoking. Surgical resection is an option for those that still do not improve.
When the damage to the superficial lamina propria is irreversible, it is possible that the formation of a scar or sulcus vocalis forms due to the loss of viscoelasticity. This theory is still open to debate, as a definitive explanation for the development of sulcus vocalis does not yet exist. Other theories include congenital development from branchial arch anomalies and other acquired etiologies such as laryngeal cancer or trauma. Currently, treatment of sulcus vocalis aims at improving mucosal wave vibration through phonomicrosurgery or inserting vocal fold implants to prevent glottic insufficiency. Conservative measures may also be indicated in sulcus vocalis.
There are several types of benign lesions encountered on the vocal fold. Among these benign lesions are vocal fold nodules. By definition, these lesions are always found on bilateral vocal cords and often seen in young women or children. The mechanism behind the development of these nodules is usually due to repetitive trauma resulting in inflammatory changes in the vocal cords. Initially, vocal fold nodules start as acute vascular vocal fold lesions that appear erythematous and edematous. Eventually, with chronic abuse, they become fibrotic and thickened white lesions. Data shows women and children have a higher incidence of vocal fold polyps because they have relatively higher frequency voices which in theory results in increased trauma caused by the repetitive collision of the vocal folds. The first line therapy for these lesions is voice therapy and other conservative measures including speech therapy, smoking cessation, and humidification of the folds. The Anatomy Of The Larynx And Its Role In Phonation Essay.
In comparison to vocal fold nodules, vocal fold polyps can be either unilateral or bilateral. These polyps are exophytic lesions most often seen at the anterior free edge of the vocal cords. Initially, the polyps can develop as translucent mucoid polyps from inflammation and chronic irritation much like vocal fold nodules. Some polyps may go on to undergo neovascularization and have a risk of hemorrhagic rupture into the vocal folds. The primary treatment of vocal fold polyps is similar conservative treatments as described above.
Several cysts occur within the vocal folds and can secondarily disrupt the natural voice production. Vocal fold cysts are subepithelial in origin and can be either unilateral or bilateral. These cysts are usually secondary to chronic irritation and may also cause reactive changes on the opposite fold. Definitive therapy is micro flap resection. An acquired subglottic cyst presents with post-intubation stridor due to obstruction of the mucous glands by an ET tube. Saccular cysts were briefly referenced earlier. Due to the many mucous filled glands in the ventricular saccule, these cysts are most often mucous filled secondary to obstruction of the mucous glands from prolonged intubation. These cysts do not communicate with the laryngeal cavity, while a laryngocele does. Laryngocele is a dilation of air of the laryngeal ventricle and is more common in adults, compared to saccular cysts which are more common in children. Cysts can be either internal or external. Internal cysts lie within the thyroid cartilage and most often present with hoarseness. External cysts produce a laryngocele sac that protrudes the thyrohyoid membrane thus presenting with a compressible mass that will increase in size with increased pressure within the larynx.
Vocal Fold Paralysis
Many etiologies of vocal fold paralysis are known, but the most common of those include neural denervation of the ipsilateral vagus or recurrent laryngeal nerve and mechanical fixation of intra-laryngeal cartilage. Initial presenting symptoms of those with unilateral paralysis include hoarseness, aspiration, and even complete asymptomatic symptomatology. Those with bilateral paralysis will also have stridor. The Anatomy Of The Larynx And Its Role In Phonation Essay. Initial workup includes both laryngoscopy and stroboscopy to asses the function of the folds. On laryngoscopy, pooling of secretions, anterior displacement of the arytenoids, and a paramedian vocal fold during phonation are the presenting features of vocal fold paralysis. Meanwhile, stroboscopy will show a glottic gap due to the insufficient vocal folds inability to close completely during phonation. Also, higher amplitude asymmetry values are often seen in vocal folds with paralysis. Another useful clinical test is laryngeal electromyography (EMG). EMG allows the differentiation between mechanical and neurological causes of vocal fold immobility as well as the time in which the vocal fold is denervated or reinnervated. In cases of vocal fold paralysis from mechanical etiologies, the EMG will be normal, with multiple action potentials from motor units that will develop into a normal pattern. Those with denervation injury, potentials are fibrillated with spontaneous positive waves while those that undergo reinnervation of the vocal fold show polyphasic motor units. This difference is significant because often the EMG will show reinnervation changes far before motor functionality of the vocal fold returns. When mechanical and neural factors are absent, secondary etiologies must be explored. Other etiologies that are less common of vocal fold paralysis include infections such as Lyme disease, syphilis, TB, and EBV, malignancy, and toxins (such as lead, arsenic, quinine, and streptomycin). Other modalities used to determine the underlying cause of vocal fold paralysis include chest x-rays, modified barium swallow, an esophagram, and labs (including CBC, a treponemal test, and Lyme titers). CT of the skull base down through the course of the vagus nerve may also be done to determine lesions of the vagus nerve. The Anatomy Of The Larynx And Its Role In Phonation Essay.