Pituitary adenomas treated with gamma knife radiosurgery:: Volumetric analysis of 100 cases with minimum 3 year follow-up

OBJECTIVE: To analyze pituitary adenoma volume changes after gamma knife radiosurgery (GKRS) in patients with 3 years of follow-up and to investigate factors that might affect these changes. METHODS: Between January 1997 and March 2004, a total of 1930 patients were treated in the Gamma Knife Unit of the Marmara University Department of Neurosurgery in Istanbul, Turkey. Three hundred sixty of these patients had pituitary adenomas (PAS). This prospectively designed clinical study documents the radiological-volumetric analysis for the first 100 of these patients with PAS who had a minimum of 3 years of follow-up and met the study requirements. Each tumor was assessed with serial magnetic resonance imaging scans after radiosurgery; at each time point, adenoma volume was expressed as a percentage of the tumor's initial volume. Volume changes were investigated relative to margin dose, the cavernous sinus infiltration, and endocrinological type of adenoma. RESULTS: At the end of the first year after GKRS, the PA volumes had decreased to approximately 90% of the initial volume on average. The corresponding approximate averages for the ends of Years 2 and 3 were 80 and 70% of the initial volume, respectively. At 3 years after GKRS, the PAS in the group with a peripheral dose of less than 17 Gy were reduced to approximately 80% of the initial volume on average. In contrast, the tumors in the patients with marginal doses of 21 to 23 Gy were reduced to approximately 60% of the initial volume at this stage. The adenomas treated with the highest marginal doses (>27 Gy) showed the earliest volume decreases after GKRS (6-9 mo after the procedure). Cavernous sinus noninfiltrating adenomas showed greater volume decreases after GKRS; on average, these masses were reduced to approximately 50% of their initial volume at 3 years. In contrast, the PAS that had infiltrated the cavernous sinus had only dropped to approximately 80% of their initial volume at this stage. The growth hormone-secreting PAS showed the maximum volume decrease with GKRS. On average, these lesions were approximately 60% of their initial volume at the 3-year stage. The nonfunctioning tumors and the prolactin-secreting adenomas showed similar volume changes over time. On average, these tumors had dropped to approximately 75 and 70% of the initial volume, respectively, by 3 years after GKRS. CONCLUSION: Gamma knife radiosurgery halts the growth of pituitary adenomas. Cavernous sinus extension and margin dose are the most important determinants of adenoma volume after this type of therapy.