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Radiotherapy and intracranial meningiomas causing visual disturbance
  1. J O’Day
  1. Correspondence to: J O’Day Victoria Parade Eye Consultants, 55 Victoria Parade, Fitzroy, Victoria 3065, Australia; justinodaybigpond.com

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Grounds for cautious optimism in the treatment of this condition

The meningiomas account for approximately 15% of intracranial tumours. Most meningiomas are benign slow growing well circumscribed tumours. The preferred mode of treatment is total surgical excision unless total removal would result in an unacceptably high morbidity.1 Certainly there have been changes to neurosurgical techniques with operative stereotaxy integrated with preoperative imaging to delineate more clearly the extent of the tumour and with it the ability to remove the lesion with less damage to surrounding structures.

However, if there is incomplete resection of the tumour then the cumulative risk of progression increases slowly over 10–15 years to 90%.2 Radiotherapy is the one technique used as adjuvant therapy that has been shown consistently to slow the rate of recurrence and sometimes to partially reverse visual loss when present.

Radiotherapy, however, has side effects as it may lead to primary axonal damage or secondary axonal damage from vascular occlusion.

Recently developed radiotherapy techniques have been introduced to try and limit the radiotherapy treatment as much as possible to the tumour and not to the surrounding tissues and fractionated stereotactic radiotherapy is one such modality.

Behbehani et al in this issue of BJO (p 130) have reported the use of fractionated stereotactic radiotherapy (FSRT) for treating parasellar meningiomas. This is a retrospective series of 13 patients and the authors have shown that in 75% of eyes the visual acuity remains stable and in 57% of eyes the visual field improved. There was a diminution in central acuity in 12.5% and a decrease in visual field in 15% of eyes. This is the first significant series of patients with parasellar meningiomas with visual field loss, who have undergone this form of radiotherapy, to be reported.

There has already been a number of published series using the same technique with optic nerve meningiomas where there has been a stabilisation in vision and occasionally a visual improvement.

There are, however, some questions that remain unanswered. A dose of 50.4 Gy was given in 28 fractions over a 5 week period. The ideal dose however for radiation treatment is not known precisely because of individual tolerance of the varying dose that will be administered to surrounding structures. The general guideline is that 60 Gy in divided fractions causes a 5% incidence of neurotoxicity. However, the problems with irradiation, particularly in slowly dividing tissues such as the central nervous system, may not be manifest for a number of years and so although there are grounds for cautious optimism from this reported series, I think that long term effects of fractionated stereotactic radiotherapy will be important to report.

Certainly the authors do report the recent article where radiation retinopathy had occurred 22 months after FSRT optic nerve sheath meningioma.

Unfortunately, it is difficult to obtain the series of patients that is large enough to provide statistically significant results. However, a European group is currently designing a prospective meningioma randomised trial of observation versus conventionally fractionated radiotherapy or radiosurgery after non-radical surgery in benign intracranial meningioma. This study will use various radiotherapy techniques and perhaps will help to further elucidate the controversy over the efficacy and side effects of radiotherapy treatment for meningioma.

This paper by Behbehani et al does, however, give us grounds for cautious optimism in the treatment of this condition and I encourage them to report on this group of patients again when there has been a longer lapse of time.

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Grounds for cautious optimism in the treatment of this condition

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