The term "fetal adenoma" has long occupied a place in the literature on the thyroid gland. The first use of this term is generally credited to Wölfler,1 who in 1883 used it to designate certain nodular tumors of the thyroid gland, which he thought arose from fetal cell rests. With an advance in knowledge, however, the concept of a fetal origin for these nodules has largely been discarded, although through usage the term persists in the literature. Today it has come to designate a distinctive type of nodule, on the general features of which most observers are agreed.
While a detailed description of a typical "fetal adenoma" will be given later (fig. 1), a few of its distinctive features may be cited here. Such a nodule is discrete, circumscribed, encapsulated and of variable size, occurring alone or multiply and presenting to the unaided eye a dull gray homogeneous substance
MURPHY WB, AHNQUIST G. ORIGIN OF FETAL ADENOMA IN THE THYROID GLAND. Arch Surg. 1937;35(2):211-233. doi:10.1001/archsurg.1937.01190140003001