Pathological findings following radiosurgery of pituitary adenomas

Pituitary adenomas represent approximately 10-20% of all primary brain tumors. Surgical resection is the mainstay of treatment for most pituitary adenomas. At times, complete surgical resection may be impossible or the adenoma may recur. The Gamma Knife has become an important neurosurgical tool for the treatment of recurrent or residual pituitary adenomas. Gamma surgery typically affords a high rate of tumor volume control but a more variable rate of endocrinological remission. When radiosurgery fails to provide a good outcome, surgical resection often needs to be repeated. At the University of Virginia during a 15-year time period, 434 patients have been treated for recurrent or residual pituitary adenomas with the Gamma Knife. Upon review of their follow-up neuroimaging studies, we have not observed a case of a radiation-induced neoplasm. The incidence of Gamma Knife-induced neoplasia is likely low and will require longer follow-up to ascertain the true incidence. Preand post-Gamma Knife histological specimens were available in 4 patients (0.92% of patients). A comparison of these specimens was significant for necrosis but not vessel wall hyaline thickening, fibrinoid necrosis, vascular occlusions, or teleangectatic dilatations. Further study must be performed to determine the histological changes that accompany the frequently beneficial effects of radiosurgery in recurrent or residual pituitary adenomas.