Preliminary Results After Multisession Gamma Knife Radiosurgery For Perioptic Meningiomas

Keywords: meningioma, optic chiasm, gamma knife, outcome, fractionated stereotactic radiotherapy

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     To evaluate the safety and effectiveness of a Gamma Knife treatment in three consecutive days (multisession) in patients with parasellar meningioma in close contact to the optic nerve and chiasm.
     Between January 2006 and April 2009 38 patients underwent multisession gamma knife treatment at San Raffaele Institute. Of those, 31 had a parasellar meningioma in close contact to the optic nerve and chiasm.  25 patients (20 females, 5 males, mean age 54 years) with minimum follow up longer than six months were included. All patients had cavernous sinus meningioma immediately adjacent to the anterior visual pathway. Preoperative decreased visual acuity was found in 11 patients while visual fields defects were found in 10 subjects. Cranial nerves palsy was found in 6 patients.
     Gamma Knife radiosurgery was delivered in three sessions with a mean prescription isodose of 6.8 Gy per session (range 6.5-7 Gy) and a mean total prescription isodose of 20.7 Gy (range 19.5-21 Gy). Mean tumor volume was 8.4 ml (median 5.3, range 0.33-34.2). Maximum dose to the optic apparatus was always below 7 Gy for each session (mean 5 Gy).
     Mean follow-up was 28 months (median 22, range 6-46). Overall tumor control rate was 100%. Tumor volumetric reduction was observed in 8 patients (32%), whereas in 17 patients (68%) no volumetric changes were recorded. No patient experienced worsening of visual function. Visual acuity improvement occurred in two patients (18%). Cranial nerve function improvement was recorded in one patient (16,6%). One patient reported an improvement of a previous visual field defect (10%). No patient had acute radiation induced adverse effects.
     This is a retrospective study.
     This preliminary experience suggests that multisession radiosurgery with Gamma Knife can be a safe and effective treatment for tumors immediately adjacent to segments of the optic apparatus.


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