This is a normal thyroid with small foci of round blue cells.

Upon closer inspection, these round blue cells are collections of C cells -- normally, you should not be able to easily detect C cells, thus, this would qualify as C cell hyperplasia.

C cell hyperplasia is the increase of calcitonin-producting C cells in the thyroid. Usually C cells are hard to find on regular H&E sections, therefore, their presence should alert you to the possibility of C cell hyperplasia.

C cell hyperplasia is associated with MEN IIa and IIb. They can evolve into nodular hyperplasia and medullary carcinoma. The RET mutation is seen in familial medullary thyroid carcinoma as well as sporadic cases of medullary carcinoma. Mutations of the trk (family neurotropin receptor) may also be involved in pathogenesis.

• Thyroid : Medullary Carcinoma