Inclusions in the human thyroid.

A survey of the thyroids of 350 infants and children suggests that the presence of thymus and parathyroid tissue within the thyroid is so common as to be classified as normal. One in a hundred thyroids contains masses of cartilage, and one in a hundred shows small foci of ciliated epithelium. Compact masses of dark-staining cells that bear a resemblance to primitive follicular plate cells are also so common as to raise the possibility of their being a normal component with, possibly, an endocrine function. It has been suggested that they produce calcitonin, but this could not be confirmed. Peculiar granular cells replacing follicle cells were also noticed.