Reduction in Thymoma Size After Pituitary Surgery for Growth Hormone–Secreting Tumor

ABSTRACT Objective: A thymoma is a rare tumor of the anterior mediastinum and may be under the control of prolactin and growth hormone (GH), as well as GH-insulin-like growth factor 1 (IGF-1)–mediated paracrine and autocrine pathways. The following case report highlights the unexpected outcome in a patient with a mediastinal thymoma after pituitary surgery for a GH-producing macroadenoma. Methods: A 58-year-old Caucasian man with a history of acromegaly caused by a pituitary macroadenoma presented with a mediastinal thymoma (proven by biopsy). The thymoma was monitored annually by imaging studies, as the patient was asymptomatic and had declined surgery. The octreotide scan was negative and tests ruled out a GH–releasing hormone (GHRH)-producing tumor. Transsphenoidal surgery for removal of the pituitary tumor was performed. Results: Following surgery, the patient's IGF-1 levels normalized and GH was adequately suppressed in an oral glucose tolerance test. Follow-up imaging after 6 weeks and 10 months of surgery showed the absence of a pituitary tumor and a marked reduction in size of the mediastinal thymoma. Conclusion: In a patient with acromegaly and a thymoma, surgical treatment of the GH-producing tumor might be expected to cause a reduction in thymoma size. Therefore, such tumors in patients with acromegaly may simply be monitored clinically. Abbreviations: GH = growth hormone; GHRH = growth hormone–releasing hormone; IGF-1 = insulin-like growth factor 1; MRI = magnetic resonance imaging; TEC = thymocyte epithelial cell