Complete surgical removal of skull base meningiomas without neurological deficit is very difficult. Hence, many neurosurgeons recommend simple observation for medium-size meningiomas. In contrast, we deal with them proactively with Gamma knife surgery before they grow and present symptoms.

     Our treatment is performed based on knowledge of microanatomy and also from microsurgical point of view.

     From January 2003 to September 2009, a total of 5105 patients were treated by Gamma Knife at our institute. Among them, 184 cases were skull base meningiomas. Seventy eight cases with more than 3 years of follow-up were enrolled for this study.

     Gadolinium-enhanced axial CISS images were used in all cases. We tried to clarify dural attachment of the tumor, and surrounding peritumoral nerves were delineated as much as possible. Center of each isocenter was gathered at the dural attachment and 80% higher isodose area was placed as wide as possible within the tumor. To avoid excess radiation to peritumoral healthy tissue, we placed each isocenter within tumor membrane. The treatment was then performed by 12Gy to the 50% isodose line.

     At an average of 42 months follow-up, tumor control rate was 98.7% and tumor shrinkage rate was 73.1%. Treatment complication (transient abducens nerve palsy) was observed in 1.3%, and brain edema in 2.6% which was, on the image, considered as a result of radiation injury to the brain stem. Evaluation of unit energy (tumor energy per unit volume of tumor) showed significantly high value in shrinkage group (p=0.03).

     This is a retrospective study.

     Our study result is well compared to many other reports as to tumor shrinkage and complication rate.

     Our results indicate that a well-designed treatment strategy and planning will produce better results than simple observation.