The C-cells: current concepts on normal histology and hyperplasia.

We describe the current concepts on the embryology, normal morphology and immunohistochemistry of a minor cell population of the thyroid, the C-cells. We also try to make delineation between the normal number of the C-cells and C-cell hyperplasia. The two types of C-cell hyperplasia, physiologic and neoplastic are defined and characterized from morphologic and genetic point of view. Their relation with thyroid pathology, especially with medullary thyroid carcinoma is discussed.