What type of fluid is found in a thyroid cysts?

The fluid found in a thyroid cysts is typically a clear or straw-colored fluid that may be thin and watery, or thicker and more viscous. It can sometimes have a brownish or reddish tinge due to the presence of blood or hemosiderin (a breakdown product of hemoglobin). The fluid may also contain protein, cholesterol, and other cellular components. In some cases, the cyst fluid may be turbid or cloudy due to the presence of inflammatory cells or debris.