Undifferentiated sarcoma of the cavernous sinus after γ knife radiosurgery for pituitary adenoma

We report a rare case of gamma knife radiation-induced undifferentiated sarcoma in the cavernous sinus. A 24-year-old woman underwent resection of a growth hormone-secreting pituitary adenoma and gamma knife radiosurgery (maximal dose 24 Gray (Gy); marginal dose 16 Gy) for residual adenoma in the right cavernous sinus. Follow-up MRI showed the disappearance of the adenoma. Fifteen years later, she developed right oculomotor nerve palsy. MRI revealed a new tumor in the right cavernous sinus. Partial removal of the tumor was performed via a transsphenoidal approach. Histological diagnosis revealed undifferentiated sarcoma. The patient received three cycles of chemotherapy containing doxorubicin and ifosfamide, then carbon ion radiotherapy (65 GyE in 26 fractions). Subsequent MRI showed tumor regression for five months. To our knowledge, this is the first report of undifferentiated sarcoma following gamma knife radiosurgery for pituitary adenoma. As patients undergoing radiosurgery face the possibility of such neoplasms developing, long-term follow-up is required.