Endocrine and Morphologic Studies of Pituitary Adenomas Secondary to Primary Hypothyroidism

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Abstract
Two patients with enlarged pituitary fossae presented with a number of features in their medical history and laboratory workup suggesting the diagnosis of “non-functioning” pituitary adenoma. Both patients had low serum thyroxine (T4) concentrations and resin T3 uptake, and one patient showed a high titer of microsomal thyroid antibodies. Both patients had high serum TSH concentrations before and after stimulation with TRH. After pituitary surgery, the serum TSH levels diminished but remained abnormally high and were suppressed by thyroid hormone administration. Light microscopic studies of the tumors, including differential staining and immunocytochemical procedures for the demonstration of TSH cells, showed cells indistinguishable from those of chromophobic adenomas. Ultrastructurally, the adenoma cells contained relatively few granules, similar to those described in “non-functioning” chromophobic tumors. Our investigations suggest that some of the patients diagnosed as having “non-functioning” pituitary tumors may have TSH-producing tumors secondary to primary thyroid failure, so that initially thyroid hormone therapy may be the treatment of choice. Surgery or radiotherapy might be reserved for the patients who develop deterioration of vision or other evidence of progressive tumor growth in spite of hormone therapy.