[Fractionated stereotactic radiotherapy for optic nerve sheath meningioma: eight cases]

Optic nerve sheath meningioma (ONSM) accounts for one-third of primary optic nerve tumors, and 2% of all meningiomas. ONSM must be distinguished from other meningiomas, in particular from cavernous meningiomas because of the different prognosis and treatment. The most frequent clinical sign is a progressive or sudden unilateral visual loss. Treatment of ONSM is still subject to discussion. This report covers a series of eight ONSM patients treated with fractionated stereotactic radiotherapy.

Between 2000 and 2006, we managed eight patients with ONSM. The average patient age was 47 years. There were five women and three men. The most frequent clinical signs were visual loss (100%), proptosis (35%), diplopia (25%). One patient was initially treated with surgery. All patient have been treated by fractionated stereotactic radiotherapy. 45 Gy in 25 fractions were delivered on the meningioma area at a rate of 5 fractions of 1.8 Gy per week. We used a Brainlab framework associated with a thermo-formed mask. A computed tomography then magnetic resonance imaging was obtained for each patient. The data was merged and planning took place on a Brainlab dosimetric console. The treatment was performed with a head-only Varion linear accelerator, with a Brainlab multi-blade collimator.

The average follow-up was 27 months. Each patient had a complete radiological and ophthalmologic exam every 3 months during the first year, then every 6 months thereafter. Tumor control rate was 100%. Vision was re-established in five patients and three patients had improvement, including one patient during treatment. 100% of proptosis and diplopias regressed. No side effect was reported.

This is still a preliminary study, but the results suggest that fractionated stereotactic radiotherapy may emerge as a primary treatment for ONSM, delaying surgery, which has proven functionally disappointing.