A thyroglossal cyst is a fibrous cyst that forms from a persistent thyroglossal duct. Thyroglossal cysts can be defined as an irregular neck mass or a lump which develops from cells and tissues left over after the formation of the thyroid gland during developmental stages.Thyroglossal cysts are the most common cause of midline neck masses and are generally located caudal to (below) the hyoid bone. These neck masses can occur anywhere along the path of the thyroglossal duct, from the base of the tongue to the suprasternal notch. Other common causes of midline neck masses include lymphadenopathy, dermoid cysts, and various odontogenic anomalies.Thyroglossal cysts develop at birth. Many diagnostic procedures may be used to establish the degree of the cyst. Signs and symptoms
Thyroglossal duct cysts most often present with a palpable asymptomatic midline neck mass usually below [65% of the time] the level of the hyoid bone. The mass on the neck moves during swallowing or on protrusion of the tongue because of its attachment to the tongue via the tract of thyroid descent. Some patients will have neck or throat pain, or dysphagia.The persistent duct or sinus can promote oral secretions, which may cause cysts to become infected. Up to half of thyroglossal cysts are not diagnosed until adult life. The tract can lie dormant for years or even decades, until some kind of stimulus leads to cystic dilation. Infection can sometimes cause the transient appearance of a mass or enlargement of the cyst, at times with periodic recurrences. Spontaneous drainage may also occur.
Cavity may refer to:

Biology and healthcare
Body cavity, a fluid-filled space in many animals where organs typically develop
Gastrovascular cavity, the primary organ of digestion and circulation in cnidarians and flatworms
Dental cavity or tooth decay, damage to the structure of a tooth
Lung cavity, an air-filled space within the lung

Radio frequency resonance
Microwave cavity or RF cavity, a cavity resonator in the radio frequency range, for example used in particle accelerators
Optical cavity, the cavity resonator of a laser
Resonant cavity, a device designed to select for waves of particular wavelengths

Other uses
Cavity (band), a sludge metal band from Miami, Florida
Cavity method, a mathematical method  to solve some mean field type of models
Cavity wall, a wall consisting of two skins with a cavity

See also
Cavitation, the phenomenon of partial vacuums forming in fluid, for example, in propellers
Cavitary pneumonia, a type of pneumonia in which a hole is formed in the lung
Cavity Search (disambiguation)
Hollow (disambiguation)