The thyroid cartilage is part of the cartilaginous skeleton of the larynx. The structure of this cartilage affects voice production. Diseases of the thyroid cartilage therefore affect the voice.
What is the thyroid cartilage?
The thyroid cartilage, with the Latin term cartilago thyroidea, represents the largest cartilage of the larynx. In English, it is referred to as thyroid cartilage. Externally, the thyroid cartilage is visible as the Adam’s apple. Especially in men, the Adam’s apple appears prominent and is the prerequisite for a deep voice. The Adam’s apple is one of the secondary male sexual characteristics. It is formed by a thickening of the thyroid cartilage under the influence of testosterone. Above the thyroid cartilage is the laryngeal cap (epiglottis), which prevents food pulp from passing into the trachea. The epiglottis is connected to the thyroid cartilage. Below the cartilago thyroidea sits the horizontal cricoid cartilage, which is hinged posteriorly to the stellate cartilages. Behind the thyroid cartilage are the vocal cords or vocal folds. They are connected to each other by articular cartilages. The cartilages are held together by various ligaments, and the larynx is suspended from the hyoid bone with the aid of a membrane.
Anatomy and structure
The thyroid cartilage is formed by two cartilage plates of hyaline cartilage. In this process, these cartilage plates are connected at the front in the middle. Toward the top, there is a small notch in the thyroid cartilage called the incisura thyroidea superior. It is even palpable from the outside. Towards the bottom, there is another smaller inconspicuous notch called incisura thyroidea inferior. Behind the thyroid cartilage, the vocal cords are stretched between the stellate cartilages. The cartilago thyroidea forms the anterior aspect of the larynx. It is still somewhat curved forward. During puberty, a thickening of this protrusion takes place in young males. The typical Adam’s apple is formed, and the voice becomes deeper. Four muscles attach to the thyroid cartilage. The sternothyroid muscle is a skeletal muscle that pulls the thyroid cartilage downward. It attaches to the linea obliqua, an oblique line structure of the thyroid cartilage. The thyrohyoid muscle is also located at the linea obliqua and is an extension of the sternothyroid muscle. By shortening the distance between the hyoid bone and thyroid cartilage, it provides closure of the larynx. As another pharyngeal muscle, the constrictor pharyngis inferior muscle lies farthest down toward the esophagus. One part of the muscle, the pars thyropharyngea, in turn begins at the linea obliqua. The other part, the pars cricopharyngea, originates at the lateral border of the cricoid cartilage. The inferior constrictor pharyngis muscle has two functions. On the one hand, it pushes the food pulp toward the esophagus during swallowing, and on the other hand, it participates in voice modulations. The cricothyroid muscle is the fourth muscle connected to the thyroid cartilage. It begins at the cricoid cartilage and extends to the anterior border of the thyroid cartilage. It is partly responsible for regulating the state of tension of the vocal cords, thereby increasing vocal frequency.
Function and tasks
Thyroid cartilage plays a major role in determining the structure of the larynx and thus exerts great influence on its function. Because of its close connection to the laryngeal musculature and the vocal cords, it is partly responsible for the closure of the larynx during swallowing and for voice production, among other things. Through this close connection, structural changes in the thyroid cartilage, such as the formation of the Adam’s apple, also lead to a deeper voice. The individual muscles of the larynx have different tasks, as already mentioned. In addition to its function as an important structural component of the larynx, the thyroid cartilage also ensures the fine-tuning of the various processes involved in voice formation. Even the smooth separation of the functions of the esophagus and trachea is due in part to the work of the thyroid cartilage.
Diseases
Isolated diseases of the thyroid cartilage are very rare. Most often, the thyroid cartilage is involved in inflammation of the larynx (laryngitis), but it is not the cartilage that is affected, only the mucosa. Laryngitis often results from viral infections. More rarely, there is a bacterial infection.However, inflammation due to autoimmune diseases is also possible. In these processes, mainly the mucous membranes are attacked. If the disease spreads to the vocal cords, hoarseness or even loss of voice occurs. Furthermore, there are various benign and malignant laryngeal tumors. Benign tumors occur more frequently than malignant ones. Here, too, the thyroid cartilage is usually not affected in isolation. A very common symptom is increasing hoarseness. More than 90 percent of the malignant forms are squamous cell carcinomas. In turn, the cells of the mucous membrane degenerate. In rare cases, however, chondrosarcoma can also occur. Chondrosarcoma is a degeneration of connective tissue cells of the cartilage. Here, too, the localization is very rare, especially in the thyroid cartilage. Chemotherapy and radiotherapy are not successful with this tumor, because degenerated cartilage cells do not respond to them. The only chance of a cure is the complete removal of the tumor. This may mean complete removal of the larynx, resulting in loss of voice. If there is swelling under the thyroid cartilage, it may also be a thyroid disease in which a goiter forms. According to the symptoms, a disease of the thyroid cartilage is superficially suspected here. However, a neighboring organ is affected.
