Gamma Knife Surgery For Trigeminal Schwannomas: Results Of A Consecutive Series With A Minimum Two To Five Years Follow Up Period

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

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     To evaluate the outcomes of Gamma Knife surgery (GKS) in patients with trigeminal schwannomas the authors compared tumor volume and imaging features with tumor control and clinical evolution.
      Fifty patients with trigeminal schwannomas were treated by the same team from 1994 to 2009. Of these 40, with minimum follow up of two years (range 24 to 213 months), were assessed: 31 were female and 9 male; the median patient age was 50 (range 19-78 years). Five patients had previous microsurgical removal. The tumor was located at the root entry zone in one cases, at the root in five, at the ganglion in fourteen and at the third branch in two; both root and ganglion were involved in eighteen patients.
     The median target volume was 3.8 cm3 and the median dose to the tumor margin was 14Gy. The tumor control rate was evaluated every six months with MR, in the first year, and then every year; when possible indicator-box volumetric measurements were performed.
     Preoperative symptoms at two-years follow up improved in 28 (70%) of 40 patients, were unchanged in 7 (17.5%) and progressed in 5 (12.5%). Four years after GKS we evaluated 23 patients (four were lost at follow up): 15 improved (65.2%), 4 were stable (17.4%) and 4 had worsened trigeminal numbness (17.4%) The tumor disappeared in 3 cases (13%), was reduced in 13 (56.5%) and was stable in 4 (17.5%). In 3 patients (13%) the volume increased and in one we repeated GKS after five years. Of six patients with recorded follow up of at least ten years one had unchanged trigeminal neuralgia and the others were symptoms free: the tumor volume was stable in all cases. In three cases the development of intratumoral cysts were observed but in no case it was necessary to evacuate the cyst.
     This was a retrospective study.
     Predictors of better treatment response included preoperative tumor volume, root or ganglion variety and GKS as primary treatment and presence of preoperative intralesional cysts. The MR appearance two years after GKS is not a definitive outcome predictor and further changes may be confirmed at 4 years follow up.
     Clinical outcome and tumor control obtained at 4 years seems to be maintained at longer follow up. Volumetric measurement and image co-registration with dedicated software help in decision making during follow up.


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