Spontaneous regression of a growth hormone-secreting pituitary adenoma following thyroidectomy for toxic multinodular goiter with superior vena cava obstruction: Report of a rare case.

Acromegaly is most commonly caused by a growth hormone (GH)-secreting pituitary adenoma; the spontaneous regression of such tumors is exceedingly rare. The present study reports the case of a 51-year-old male patient with long-standing acromegaly who developed a toxic multinodular goiter complicated by superior vena cava obstruction (SVCO). An initial evaluation revealed a pituitary macroadenoma measuring 19x17x16 mm, with elevated GH and insulin-like growth factor-1 (IGF-1) levels, consistent with acromegaly. The patient was treated with a somatostatin analog and metformin for glycemic control, followed by carbimazole in preparation for thyroidectomy. He subsequently underwent urgent total thyroidectomy for compressive symptoms due to SVCO. Post-thyroidectomy, he experienced marked clinical improvement, including the resolution of dyspnea, improved sleep quality, enhanced mood and partial regression of acromegaly symptoms. Biochemically, IGF-1 normalized within 6 months of total thyroidectomy, and an MRI demonstrated the progressive shrinkage of the pituitary adenoma, reducing to 8x6x5.5 mm at 1 year without neurosurgical intervention. Possible mechanisms for regression include perioperative pituitary apoplexy, spontaneous ischemia, or altered vascular dynamics following thyroidectomy. The present case report highlights the importance of reassessing pituitary adenomas following the treatment of coexisting endocrine or compressive disorders and suggests a potential role of vascular factors in pituitary tumor regression.