Background: Ectopic thyrotropin (TSH)-secreting tumors are extremely rare. To our knowledge, only three cases have previously been reported so far, but the tumors were not studied ultrastructurally and in vitro. We present a case that was extensively examined to gain deeper insights in terms of the histopathological features and hormonal secretion profile of the tumor.

Patient findings: A 49-year-old female complained of nasal obstruction for 15 years and thyrotoxicosis for one and a half years. Except for a high basal TSH with concomitantly elevated free tri-iodothyronine (FT3) and free thyroxine (FT4) levels, her pituitary hormone profile yielded normal results. Magnetic resonance imaging revealed a 2 cm × 2 cm mass in the nasopharynx, which showed an increased tracer uptake on octreotide scintigraphy. Preoperative treatment with octreotide effectively reduced serum TSH, FT3, and FT4 to normal levels. The mass was endoscopically removed via an endonasal approach. Immunophenotyping and hormone determination of cultured cells confirmed that the mass was a plurihormonal TSH-/growth hormone (GH)-/prolactin (PRL)-producing adenoma. Co-expression of TSH and GH was found in most cells. Electron microscopy showed that the adenoma was formed by a single cell type, with secretory granules of small size. In vitro studies demonstrated that octreotide reduced both TSH and GH secretion.

Summary: We report an ectopic TSH-secreting tumor, which had plurihormonal secretion in vitro, including TSH, GH, and PRL. Histologically, it mimicked a TSH-secreting pituitary adenoma. Octreotide was useful in the diagnosis and treatment of this ectopic TSH-secreting tumor.

Conclusions: Ectopic TSH-secreting tumors are extremely rare. In terms of hormone secretion profile, histological characteristics, and response to octreotide, they are similar to pituitary TSH-secreting adenomas, suggesting that they are of identical cell origin.