Q. A 7-year-old child presents to the clinic with a neck mass that has been gradually increasing in size over the past few months. The child's mother reports that the mass is painless and has not caused any difficulty with breathing or swallowing. Physical examination reveals a cystic mass in the anterior neck, located near the midline. The mass moves with tongue protrusion and is not fixed to surrounding structures. Further evaluation, including ultrasound and a fine-needle aspiration biopsy confirms the diagnosis. What is the most likely diagnosis?