Papillary carcinoma of thyroid metastatic to the pituitary gland.

We describe a 35-year-old woman who presented with diabetes insipidus caused by metastatic papillary carcinoma of the thyroid involving the pituitary gland, 25 years after treatment for a papillary carcinoma of thyroid and 17 years after treatment for multiple pulmonary metastases. The literature contains 10 previously described cases of metastatic thyroid carcinoma involving the sella, but only 2 of these cases had unequivocal metastases to the pituitary gland, making the present case, to our knowledge, the third reported case of unequivocal hematogenous metastasis of thyroid carcinoma to the pituitary gland. The pituitary tumor was removed by transsphenoidal surgery, and the tissue was examined by conventional histology, extensive immunohistochemistry, and electron microscopy. The findings confirmed the tumor to be papillary thyroid carcinoma. To our knowledge, this is the first report citing use of thyroid transcription factor-1 to establish a thyroid source of a pituitary metastasis.