Pituitary thyrotropic tumour secondary to long-standing primary hypothyroidism.

Pituitary neoplasms in primary myxoedema are rare and previously reported cases have mostly been described as chromophobe adenomas. None of them were subjected to modern methods of study. A 26 year-old woman with untreated primary hypothyroidism developed a pituitary tumour which produced bitemporal hemianopsia. Histochemical and ultrastructural studies characterized the tumour cells as thyrotrops. The secretory granules present had a mean diameter of 110 mum and were membrane-bound and surrounded by clear halos. Many of the tumour cells were actively secreting. They had reduced numbers of granules, possessed expanded Golgi complexes, abundant rough endoplasmic reticulum and free ribosomes. Cytoplasmic microfilaments were also seen. A possible mechanism of production of this tumour is discussed.