Objective To analyze the neuro-imaging and surgical pathological changes of meningiomas in different time intervals after failed Gamma Knife treatment,to provide more pathological evidence of the clinical effect of a focused single high-dose gamma irradiation.Methods In this study,32 patients with meningiomas underwent craniotomy after failed GKS.There were 13 male and 19 female patients with a mean age of 51.3 years (range 19-73 years).The time interval between radiosurgery and craniotomy was 2 to168 months (median 27.5 months),and more than 5 years in 12 cases.The histopathological grade of meningiomas revealed WHO Ⅰ in 21 cases,WHO Ⅱ in 9,and WHO Ⅲ in 2.There were 18 patients who had open surgery before GKS,and 16 patients were treated by GKS with detail plan data in our center.All the radiological and clinical data have been analyzed before surgery.Histopathological investigations were performed on surgical pathology materials,and the proliferative activity of tumor cells were compared before and after GKS in 8 cases.Results Most of the patients underwent later craniotomy with clinical symptoms and signs aggravating.In the neuro-imaging,the tumor was significantly enlarged in 16 cases; tumor swollen with peripheral edema in 10; tumor unchanged in 2; shrinkage in 2;tumor bleeding in 2.A hisopathological study revealed that SRS evokes coagulative necrosis of tumor parenchyma and stroma,the apoptotic cells increasing,and then scar tissue is gradually replaced until years,even more than ten years.Also,the indirect affect of tumor controlled was proliferative vasculopathy induced by irradiation,that the tumor cell cannot get blood supply due to narrowing of the lumen,until its complete obliteration.Those pathological changes are no matter what subtype meningiomas.There was not any increase of the tumor cell proliferative activity pathologically before and after gamma knife treatment in our specimens.The main reason of patients,who underwent repeat open surgery or GKS,was due to the factor of the tumor itself.Conclusions Radiosurgery is a relatively effective treatment modality for intracranial meningiomas at the small and deep site,and/or the recurrence after open surgery,but it is not preferred GKS when the tumor is symptomatic because of the mass effects.The radiobiological effect of GKS treating meningiomas is mainly both cellular effects and vascular mechanisms.For atypical meningioma,the patients need comprehensive treatments.This ionizing energy of high dose irradiation has not excited the increase of tumor cell proliferative activity in our observation.