Hypothyroidism Following Endoscopic Endonasal Resection of Thyrotropin-Secreting Pituitary Adenoma: A Case Series

Background: Thyrotropin-secreting pituitary adenomas (TSHomas) are rare tumors, representing a unique subset of pituitary adenomas. The standard treatment for TSHomas is endoscopic endonasal resection. While the main intent of this surgical procedure is to alleviate hyperthyroidism, postoperative hypothyroidism has emerged at our institution as an interesting sequela. Recognizing the potential for this outcome is essential for appropriate postoperative management, patient counseling, and further scientific examination.

Methods: We performed a retrospective review of patients who underwent endoscopic endonasal resection for TSHoma at our institution between 2010 and 2023. Demographic details, preoperative and postoperative thyroid function tests, pituitary imaging characteristics, and surgical details were extracted from medical records.

Results: We identified six patients in our prospective adenoma cohort of 1,000 patients . The mean age at presentation were 54 years of age at presentation. Predominant presenting symptoms included weight loss and vision deterioration. The preoperative thyroid function assessments averaged as follows: free T4 (thyroxine) 1.88 ng/dL, free T3 7.43 pg/mL, and thyroid stimulating hormone (TSH) 32.076 uIU/mL. Immediate postoperative hormonal levels were: free T4 1.1 ng/dL, free T3 5.73 pg/mL, and TSH at 3.78 uIU/mL; four of the six thyroid panel measurements indicated hypothyroidism. Three of the four required early treatment, one was observed and eventually went on replacement by 3 months. Prior to the procedure, five patients had been treated for hyperthyroidism with methimazole. All six went into hyperthyroid remission at last follow up (range 3–60 months).

Discussion: The development of hypothyroidism may occur following resection of TSH-secreting pituitary adenoma. We suspect this is a similar mechanism to post-Cushing’s cortisol crash whereby the pituitary gland is chronically suppressed and isn’t primed for nonadenoma production of TSH. The possible transition from a hyperthyroid state to hypothyroid state postoperatively demands vigilant early peri-operative monitoring and medication adjustment. Ideally, larger case series of these rare lesions can be cultivated to provide more granular insights into the mechanism and peri-operative management of these patients.