The epiglottis is a cartilaginous flap that covers the laryngeal inlet upon swallowing. In essence, it covers the laryngeal inlet upon swallowing in order to prevent food from entering the larynx. Dysfunction of the epiglottis results in dangerous dysphagia and could cause aspiration pneumonia. In this article we will discuss the development, blood supply, nerve supply, lymphatic drainage and functions of the epiglottis.
The epiglottis develops from the fourth pharyngeal arch. It becomes visible during development at 5 weeks of gestation.
The epiglottis is a leaf shaped flap of fibrocartilage covered by mucosa on its lingual surface, and functions to cover the laryngeal inlet upon swallowing. This prevents food from passing into the larynx.
The cartilage arises from a stem like base. It gains attachment from the dorsal surface of the thyroid cartilage (via the thyroepiglottic ligament), the tongue (via the median epiglottic folds), the pharynx (via the lateral epiglottic folds) and its sides are attached to arytenoid cartilages by aryepiglottic folds. The inferior part of the anterior surface has hyoepiglottic ligament which connects it with hyoid bone. It projects superodorsally in an oblique direction.
It sits upright when breathing is taking place, and hence allows air to be exhaled and inhaled from the lungs. The space between the root of the tongue in front and the lingual surface of the epiglottis is termed the epiglottic vallecula which is present on each side of median folds. The epiglottis has some taste buds that are innervated by the fibers of vagus nerve from the inferior ganglion.
The epiglottis has a lingual and laryngeal surface, the former is consistent with the oropharynx posteriorly, and is covered in non-keratinized stratified squamous epithelium. This epithelium also covers the tip of the laryngeal surface that may occasionally come into contact with the bolus of food. The laryngeal surface consists of respiratory epithelium, which consists of pseudostratified ciliated epithelium with goblet cells (which secrete mucus), and is therefore consistent with the rest of the laryngeal epithelium. This surface forms the anterior wall of the laryngeal vestibule. There is a pre-epiglottic space between the lingual surface of epiglottis and thyrohyoid membrane, this space contains the adipose tissue.
During swallowing, the hyoid bone elevates, which causes the epiglottis to flap dorsally to cover the laryngeal opening. This is achieved by three muscles; the aryepiglottic, the thyroarytenoid and thyroepiglotticus muscles.
The epiglottis is one of the three large unpaired laryngeal cartilages, the other two being the book shaped thyroid and the signet ring shaped cricoid cartilages. The thyroid notch is also termed the laryngeal prominence/Adam’s apple.
There are also three paired cartilages i.e. the arytenoid, corniculate and cuneiform. The three paired cartilages are intrinsic to the larynx itself, and responsible for phonation. The arytenoid cartilages are attached to the vocal ligaments and are pyramidal in shape. The anterior surfaces gives rise to a cartilaginous projection called the vocal process. This gives rise to the cricoarytenoid muscles that run within the superior borders of the lateral margins of the quadrangular membrane (covers the laryngeal opening laterally upon swallowing). The small corniculate cartilages sit on the apices of the arytenoid cartilages. They are found in the posterior part of the aryepiglottic folds. The cuneiform cartilages lie just in front of the corniculate cartilages within the substance of the aryepiglottic folds themselves, and can be seen as whitish elevations. The hyoid bone is not part of the larynx, but gives rise to a number of muscles that assist with movement of the larynx.
The recurrent laryngeal nerves enter the larynx by passing in the groove between the trachea and oesophagus. The nerves innervate the muscles of the larynx (aside from the cricothyroid). The sensory supply of the epiglottis comes from the internal laryngeal branch of superior laryngeal nerve (branch of vagus nerve).
The epiglottis gains its blood supply from the superior laryngeal artery, which is a branch of the superior thyroid artery (a branch of the external carotid artery). This enters the larynx by passing through an opening of the thyrohyoid membrane. Lymphatic drainage of the epiglottis occurs along the superior laryngeal artery that drains to the deep cervical lymph nodes. Venous drainage is from the superior and inferior laryngeal veins that follow the same course as the arteries, and drain into the internal jugular vein and the left brachiocephalic vein respectively.
Epiglottitis - This is a life threatening condition caused by Haemophilus influenza B bacteria, resulting in inflammation and therefore airway obstruction. Symptoms include fever, drooling, difficulty breathing, malaise, tripod positioning, inspiratory stridor and severe dysphagia. An endotracheal tube is attempted, but if the swelling of the airway does not permit it, a needle cricothyroidotomy is performed.
Laryngeal cyst - This can form anywhere in the larynx, but most commonly forms in the epiglottis and vallecula (the recess between the posterior surface of the tongue and the lingual surface of the epiglottis). Patients may present with inspiratory stridor and shortness of breath.
Invasion of pre-epiglottic space in carcinomas - Carcinoma of the infrahyoid portion of the epiglottis often extends into the preepiglottic space.
- The epiglottis is a leaf shaped cartilage that covers the laryngeal inlet upon swallowing.
- It’s sensory innervation is from the internal laryngeal branch of superior laryngeal nerve, the motor innervation is from the vagus nerve.
- The blood supply is from superior laryngeal arteries.
- The lymphatic drainage follows the superior laryngeal artery to the deep cervical lymph nodes.