Thyrotroph cell adenoma of the human pituitary gland associated with primary hypothyroidism: clinical and morphological features

The morphological features of a pituitary adenoma resected from a 39-year-old woman with hypothyroidism have been investigated. Hypothyroidism followed radioactive iodine treatment of pre-existing hyperthyroidism, presumably Graves' disease. Blood TSH was low during a euthyroid interval and was elevated above normal with the onset of hypothyroidism. The presence of a small amount of TSH was demonstrated in the tumour by radioimmunoassay. By conventional histology the tumour was a chromophobe adenoma. Some fine secretory granules stained with aldehyde thionin but were negative with PAS and contained no immunoreactive TSH. By light and electron microscopy, the tumour cells differed from thyroid deficiency cells. They were small and angular, containing numerous microtubules and small spherical secretory granules, oriented mainly along the plasma membranes. The tumour was considered to represent a thyrotroph cell adenoma, arising from protracted overstimulation secondary to chronic thyroid hormone deficiency.