A 23 year old female presented with a swelling of her neck that moved upwards on protrusion of tongue. What is the next appropriate investigation?

The key is A. FNAC. [The diagnostic investigation of thyroglossal cyst is FNAC. Then we palpate for thyroid tissue. If absent we do any one of following to confirm the absence of thyroid tissue: ultrasonography, CT scanning, thyroid scanning or MRI. If there is normal thyroid tissue we go for more aggressive Sistrunk's operation but if there is no normal thyroid tissue [in that case thyroglossal cyst itself may be the only source of thyroid tissue] we do conservative surgery and preserve some portion of cyst with thyroid tissue].