Object: Thyrotropin-secreting pituitary adenomas are rare lesions of the endocrinological system. Although introduction of a hypersensitive radioimmunoassay for thyrotropin enables the recognition of inappropriate secretion of this hormone, the aforementioned lesions remain uncommon and unfamiliar to most neurosurgeons. It has been reported previously that surgical cure of thyrotropin-secreting adenomas is more difficult than in other functional adenomas because of the large size and invasive features of the former. However, the long-term outcome after surgery has not been well documented. The authors report on a surgical series of 16 patients with thyrotropin adenoma and the results of long-term follow up.
Methods: Sixteen patients ages 23 to 62 years (12 women and four men) underwent transsphenoidal removal of thyrotropin adenomas between 1983 and 1999. These patients had the syndrome of inappropriate thyrotropin secretion (SITS) with pituitary mass lesions. Four of the patients had undergone previous subtotal thyroidectomy and/or radioiodine thyroid ablation, and 11 had been treated with antithyroid medication. Radiological investigations demonstrated macroadenomas in 14 patients, and 10 of those had cavernous sinus invasion. Surgical findings showed unusually fibrous and firm tumors in 13 (81.2%) of 16 patients. Preoperative octreotide administration was revealed to be effective for serum thyrotropin reduction as well as tumor shrinkage. Transsphenoidal surgery was performed with no morbidity resulting. Surgical remission was achieved in 10 (62.5%) of 16 patients, and total remission was achieved in 14 patients (87.5%) with a combination of additional radiation or medical therapy. In the other two patients, SITS persisted because of tumor rests in the cavernous sinus. Therefore, radiation and/or antithyroid therapy was administered. In the mean follow-up period of 7.5 years (range 11 months-15.8 years), no recurrence of tumor was observed on magnetic resonance images, whereas recurrence of SITS was found in two patients with no tumor regrowth. In addition, coexistent primary hyperthyroidism was found in two other patients despite remission of SITS after surgery.
Conclusions: Transsphenoidal surgery can achieve a good long-term outcome in patients with thyrotropin-secreting pituitary adenomas if surgery is performed before these become larger, invasive tumors. In the authors' experience, thyrotropin-secreting adenomas are fibrous and firm, which makes it difficult to achieve surgical remission. In addition, even satisfactory resection of the tumor sometimes results in recurrence of SITS or hyperthyroid symptoms due to coexistent primary hyperthyroidism. It is emphasized that a careful follow-up review is necessary after surgery, especially in patients with a long preoperative history of hyperthyroidism.