Abstract
A 63-year-old woman visited our hospital with complaints of swelling and pain in the right thigh. A specimen was taken from the tumor of the right femur, and through histological examination, the tumor was found to be a metastatic tumor of the thyroid gland. Radioiodine treatment (NaI 131) was applied after total thyroidectomy and bilateral modified neck dissection. Clinically, this thyroid tumor is apparently malignant because of its osseous metastasis. However, both thyroid tumors and metastatic right femoral tumor appeared to be follicular “adenomas” according to the standard pathologic criteria and no definite evidence of malignancy was found in spite of careful histopathological examination. We diagnosed this case as the so-called metastasizing goiter and classified this lesion as a subtype of well-differentiated follicular adenocarcinoma. To clarify the entity of this lesion, we need close, long-term observation and adequate standard criteria for identifying well-differentiated follicular adenocarcinoma to differentiate it from follicular adenoma.
