Why does a thyroglossal duct cyst shrink?

Thyroglossal cyst: The cystic cavity may drain its contents to the skin at any time. This in effect may cause it to "shrink" although the cyst itself is still present and the abnormal tissue cavity will likely refill itself. Most of these aren't found until adult life, and most present as infections. This cyst can extend from the tongue down into the neck and must be carefully evaluated and possibly removed.

Thyrogloss duct cyst: the most common congenital anomaly of the neck. The pathology typically presents in children around age 6. A thyroglossal duct cyst is a very benign condition and normally disappears.