A thyroglossal duct cyst is a remnant of the pathway that the thyroid gland follows in its development from the back of the tongue to the neck. It normally contains thick, clear fluid. If not removed it tends to slowly enlarge over time and there is a risk of infection. If the cyst becomes infected, this causes pain and discomfort and treatment with antibiotics is usually required. In some cases a minor operation to drain any pus has to be performed before a final operation to remove the cyst. In contrast, a dermoid is a collection of skin cells trapped usually quite deeply under the skin surface. They are common in the head and neck area but can occur elsewhere in the body. Again, they tend to slowly enlarge with time and can become infected. Occasionally the cyst may rupture if the child knocks it against a firm surface.