We describe a 35-year-old woman who presented with diabetes insipidus cause
d 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 co
ntains 10 previously described cases of metastatic thyroid carcinoma involv
ing the sella, but only 2 of these cases had unequivocal metastases to the
pituitary gland, making the present case, to our knowledge, the third repor
ted case of unequivocal hematogenous metastasis of thyroid carcinoma to the
pituitary gland. The pituitary tumor was removed by transsphenoidal surger
y, and the tissue was examined by conventional histology, extensive immunoh
istochemistry, 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.