This study assesses the long-term efficacy of fractionated conformal radiotherapy for the management of primary optic nerve sheath meningioma.

Study design

The authors performed a retrospective chart review of adult patients treated with fractionated conformal radiotherapy (FCRT) for primary optic nerve sheath meningioma between 1995 and 2007.

Outcomes

The authors included data from the 16 patients who had at least 10 years of follow up. Visual improvement or worsening was defined as a gain or loss, respectively, of two lines of Snellen visual acuity (VA). Twelve percent of the patients had biopsy-proven meningiomas. Patients received a mean cumulative dose of 50 Gy (range 36–54 Gy). At last follow up, 31% of patients had visual improvement, 56% had no change and 13% had worsened VA. Two patients developed radiation retinopathy, one of which suffered VA loss due to it.

Limitations

This is a retrospective study; ideally a prospective study with defined treatment protocols and examination methods (including OCT) would be designed. As there were multiple treatment centers, the patients underwent FCRT protocols at the discretion of the radiation oncologist at their respective institutions. Although the diagnosis can usually be made clinically or radiologically, only 12% of patients were biopsy proven. Thus, there is the possibility that one or more mimickers (e.g., inflammatory conditions) could have been included in the study group. In addition, the location of the meningioma was somewhat variable, with the majority in the orbital segment of the optic nerve, but some in the canalicular and intracranial compartments.

Clinical significance

These findings confirm existing evidence of radiotherapy’s effects on primary optic nerve sheath meningiomas, with a long period of follow up. These are very valuable data, as radiation-related side effects can take years to manifest. In addition, this study demonstrates the durability of the treatment. Although biopsy may be needed when the diagnosis is in question, optic nerve sheath meningiomas should not be treated with surgery. In fact, attempted surgical excision usually results in visual loss. Treatment with FCRT may result in radiation side-effects, in particular radiation retinopathy. This study did not include patients treated with proton therapy, and it may be interesting to evaluate if proton therapy would result in fewer side effects.