[Prolactinoma in a child showing high MIB-1 labeling index: a case report]

We report a very rare case of a prolactin secreting pituitary tumor (prolactinoma) which occurred in a 12-year-old boy. The tumor showed an extremely high MIB-1 index. The clinical implication in the postoperative management of childhood prolactinoma is discussed. The patient showed right third nerve palsy, and MRI revealed a pituitary tumor invading the right cavernous sinus. Preoperative hormonal evaluation showed a very high prolactin level (2800 ng/ml). The patient underwent transsphenoidal surgery, and the third nerve palsy disappeared just after the procedure. MIB-1 index obtained by using immunostaining was 18.9%. Postoperative prolactin level remained high (2200 ng/ml), and the patient was treated with 10 mg/day of bromocriptine. Prolactinomas in children with high MIB-1 index show resistance to treatment with bromocriptine. In the postoperative management of a childhood prolactinoma, it should be considered how to control sufficiently high serum prolactin level to expect sexual development while preserving other normal residual pituitary functions. If control with bromocriptine, fails radiation treatment should be adopted with careful observation of the increase in height and the progress of sexual development of the patient.