This patient has a Thyroglossal Duct Cyst.
These cysts often form inchildhood and are caused by cystic expansion of the remnant of the tract that forms as the thyroid gland descends from the tongue base to the neck. Often, these cysts are small, asymptomatic, and go untreated.
See more cases like this on Figure 1.
Photo credit: Figure 1 Medical Images/Abdul Mukaddem Mashud