INCE GKS was introduced in the 1960s as a less inva- sive treatment method for functional disorder, the indication has been extended to many kinds of in- tracranial diseases. Intracranial meningiomas are one of the common indications for GKS, especially those located at the skull base. 4,5,7,8 Gamma knife surgery has not, however, been commonly performed for superficially located menin- giomas because it is relatively easy to resect such tumors and there is a high incidence of complications associated with peritumoral edema after GKS. 1,3,11,14–17 Recently, inci- dental or asymptomatic meningiomas have been found more frequently and patients seem to prefer less invasive treatments. The authors present their experience of GKS for superfi- cially located meningiomas with special emphasis on the development of high signal intensity on T 2 -weighted MR images and its significance. With this analysis, the authors document the feasibility of GKS for superficially located meningiomas and suggest a suitable dosimetry. Clinical Material and Methods Patient Population Between January 1998 and March 2003 GKS was per- formed in 28 patients with 31 superficially located menin- giomas. Twenty-six lesions in 23 patients with follow-up neuroimaging of 1 year or more form the basis of this study. The mean clinical and imaging follow-up period was 33 months (range 12–75 months). The distribution of tumor sites was falx eight, parasagittal six, tentorium five, and convexity seven. Twenty-two tumors were above the tento- rium. The male/female ratio was 1:22. The mean patient age was 59 years (range 43–73 years). Nine patients were symptomatic (six with headache, three with mild hemipare- sis). Gamma knife surgery was the primary treatment in 21 patients. The reason for this in seven cases was the lesion’s location adjacent to an eloquent area of the brain and in one patient the medical condition was poor. The remaining 13 patients receiving GKS as the primary treatment for their asymptomatic lesions did so at their own request. Two patients were treated for postoperative residual tumors. Gamma knife surgery was performed with the Leksell J. Neurosurg. / Volume 102 / January, 2005 J Neurosurg (Suppl) 102:255–258, 2005 Gamma knife surgery of superficially located meningioma DONG GYU KIM, M.D., CHI HEON KIM, M.D., HYUN-T AI CHUNG, PH.D., SUN HA P AEK, M.D., SANG SOON JEONG, R.N., DAE HEE HAN, M.D., AND HEE-WON JUNG, M.D. Department of Neurosurgery, Seoul National University College of Medicine, and Clinical Research Institute, Medical Research Center, Seoul National University Hospital, Seoul, Korea Object. The authors analyzed tumor control rates and complications in patients with superficially located menin- giomas after gamma knife surgery (GKS). Methods. Between 1998 and 2003, GKS was performed in 23 patients with 26 lesions in whom follow-up imaging for 1 year or more was available. The male/female ratio was 1:22. The mean age was 59 years. The median tumor vol- ume was 4.7 cm 3 , and the mean margin dose was 16 Gy at the 50% isodose line. Peritumoral edema was revealed on magnetic resonance (MR) imaging in four patients before GKS. Magnetic resonance imaging and clinical examina- tions were performed every 6 months after GKS. The mean follow-up duration was 32 months. The tumor shrank in eight cases, was stable in 17, and enlarged in one; thus 25 (95%) of 26 tumors were controlled. A peritumoral high signal on T 2 -weighted MR images was found in eight lesions and preexisting edema was aggra- vated in three lesions after GKS. Ten of these 11 patients complained of severe headache, and three patients experi- enced neurological deficits at the same time after a mean latency of 3 months; however, high signal was not demon- strated on imaging before 6 months on average. Steroid agents, when required, gave relief to all patients. The complication rate was 43% (10 of 23 cases). High signal disappeared in nine patients and decreased in the remaining two. High signal was associated with a high integral dose and a large tumor volume. Tumor shrinkage at the last fol- low-up examination was more prominent in the patients with symptomatic high signal (p = 0.03). Conclusions. There was a good tumor control rate with a high complication rate. Longer follow up of more patients is needed. Adjusting the dose–volume relationship should be considered to reduce complications. KEY WORDS • meningioma • gamma knife surgery • edema • superficial • peritumoral S 255 Abbreviations used in this paper: GKS = gamma knife surgery; MR = magnetic resonance.