Tumor Control And Cranial Nerve Preservation After Gamma Knife Surgery For Trigeminal Schwannomas.

Keywords: schwannoma, gamma knife, trigeminal schwannoma, outcome, skull base

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     To determine the tumor control and cranial nerve preservation rates after Gamma Knife surgery (GKS) for Trigeminal Schwannomas (TS).
     A retrospective cross-sectional analysis of patients undergoing GKS for unilateral TS was performed at a national hospital. Exclusion criteria were tumors greater than 19 cc in volume and a follow-up of less than six months. All patients were treated with the Unit B platform (Elekta AB, Stockholm, Sweden).
     Radiation safety limits for the Optic apparatus and brainstem were 8 and 12 Gy respectively.
     From May 1997 till April 2009, 25 cases of TS (13 male; 2 female) of mean age 37.2 years underwent GKS. The commonest presenting symptoms were facial numbness (16, 64 %), facial pain (8, 32 %), hearing impairment (4, 6 %) and diplopia (4, 16 %). 21 cases underwent primary and four patients underwent secondary GKS. The mean tumor size was 4.35 cc (range 0.27-12.8 cc). A median 12 Gy prescription dose (range 10.3-15Gy) was administered at the 50% isodose (range 47-50%) to cover on an average 91 % (range 90-98%) of the tumor using eight isocenters (range 1–13). At a mean follow up of 26.3 months (range 6-87 months), the rate of new onset cranial neuropathy was 8.3% (2/24) while the cranial nerve preservation rate in patients with pre-existing deficits was 96.3% (26/27). Two patients developed an increase in tumor size after GKS of whom one required retreatment. The actuarial 60 month tumor control rate was 95.5%. Both the patients in whom radiological progression was noted had a tumor volume greater than 8 cc. Progression free survival in patients with a tumor volume exceeding 8cc was 50% (2/4) while it was 100% (18/18) in smaller tumors.
     This is a retrospective study.
     GKS is a safe and effective treatment for TS less than 8 cc in volume.


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