Gamma Knife radiosurgery (GKS) has been settled down as one of main treatment methods for metastatic brain tumors. However, some metastatic lesions treated by radiosurgery could be recurred and eventually required surgical resection.

     We would like to evaluate the recurrence pattern, duration from GKS to resection, and histopathologic findings of resected tumors.

     From May 2005 to February 2010, we retrospectively reviewed the medical records, imaging results, and histopathologic results of the 21 resected metastatic brain tumors (15 patients) which had been previously treated by GKS.

     We used a volumetric method to evaluate the size of mass and an edema index to evaluate the peritumoral edema.

     The median time interval between GKS and resection was 8.4 months (range 1.5 - 11.8). Mean KPS score was 86.3, 76.5, and 82.3 at the time of GKS, resection, and 1 month after resection, respectively. Mean volume of tumor at the time of GKS was 6.7 cm3 (range 0.4 - 25.4) and 20.9 cm3 (range 3.5 - 131.5) at the time of resection. Cerebellum is the most frequent location (11 lesions) and lung is the most frequent primary origin. Fourteen lesions showed transient decrease of mass after GKS and then increased. Seven lesions showed continuous growing after GKS. In histopathologic examination, necrotic portion was varied according to the primary origin.

     This was a retrospective study.

     Short term follow-up is mandatory after radiosurgery for metastatic brain tumors.

     If the mass effect is symptomatic, a surgical removal of the lesion should be considered even when recurrence and radiation effect cannot be differentiated.