Thyrotropin-secreting
pituitary adenomas have been diagnosed more frequently as radiographic techniques and biochemical assays have improved; however, they remain uncommon and are unfamiliar to most neurosurgeons. This report concerns eight patients with
hyperthyroidism, inappropriately elevated levels of serum
thyrotropin and alpha-subunit, and radiographic evidence of
pituitary tumor. All underwent surgery and had pathological confirmation of a
thyrotropin-secreting
adenoma, and most had been subjected to prior ablation of the thyroid gland. Only one
tumor was a microadenoma; the others ranged in size from 1.4 to 12 cm, and invasion of parasellar structures was common.
Thyrotropin,
triiodothyronine,
thyroxine, and alpha-subunit were measured preoperatively and at intervals postoperatively. Coexistent hormonal abnormalities (which occurred in all patients) included
acromegaly and
hyperprolactinemia and were also monitored. All four patients who had
tumors less than 2 cm in diameter remain alive. Complete extirpation of
tumor in these patients produced rapid correction of all hormonal abnormalities and resolution of clinical
hyperthyroidism. The other four patients had larger invasive
tumors: two died soon after surgery, one died of disseminated
tumor 8 years after presentation, and one remains alive with
residual tumor.
Tumors secreting
thyroid-stimulating hormone are less easily cured by surgery than are other types of
pituitary adenoma because of the large size and invasive features that many attain during the delay to diagnosis; medical
therapy can subdue the
tumor but not cure it. The experience with these patients establishes the importance of early diagnosis and surgical excision for successful treatment, and demonstrates the utility of modern diagnostic techniques for finding these lesions. As occurs in Nelson's syndrome after
adrenalectomy for
Cushing's disease, ablation of the target organ may allow the
tumor to convert to a more clinically malignant form which is resistant to cure.