What is the substance of a nodule on the thyroid gland?

A thyroid nodule is simply a mass of extra thyroid cells within the thyroid gland, states the American Thyroid Association. The nodule is comprised of the same cells that make up the gland itself, but it is an abnormal growth.

The composition of the thyroid cells in a nodule can vary, according to MedlinePlus. The nodule may be solid or filled with fluid, and the latter classifies it as a cyst. It can also consist of a single nodule or group of nodules which are either hard or soft.

Furthermore, the composition of a single nodule or among nodules in a group can be inconsistent, according to research published by the Radiological Society of North America. A portion of a nodule may be cystic while the rest is calcified, or solid. Likewise, some nodules in a group can be cystic while some are solid.