Optic Nerve Sheath Meningiomas The Role of Stereotactic Radiotherapy

R. Smee, M. Schneider, J. Williams

Department of Radiation Oncology, Prince of Wales Hospital, Randwick, Australia

Abstract

Purpose: Primary orbital meningiomas are rare, the usual site of origin being the optic nerve sheath. These represent 1-2% of all meningiomas. This is a review of a single centre's experience. Materials and Methods: Between 1990 and February 2004 26 patients were referred and 16 patients were treated by radiotherapy (mean age 51 years). This retrospective study evaluated 16 patients - 18 tumours (1 patient with NF2 had bilateral optic nerve tumours and 1 optic nerve was treated twice). Nine patients were treated with newly diagnosed lesions, and 7 recurrent after prior treatment including radiotherapy for 1 patient. The median duration of symptoms to onset was 2 months. Treatment consisted of stereotactic radiosurgery (median dose 20 Gy) where vision was not a consideration, and fractionated SRT (median dose 5,040 Gy in 28 fx) for vision preservation. Results: Median follow up is 46.8 months. Recurrence after SRT occurred in 1 patient (a geographical miss) leading to progressive disease and blindness, this new lesion was treated with stereotactic radiosurgery, the tumour controlled with subsequently some vision improvement. Only one other patient had progressive disease, thus for an ultimate local of 94%. For fractionated patients only the above patient had worse vision after treatment. Conclusion: Radiotherapy provides high local control, utilising fractionated treatment provided it covers the full length of the nerve, is necessary to have the option of preserving vision.

Copyright © 2006 S. Karger AG, Basel

Optic nerve sheath meningiomas (ONSM) are uncommon benign tumours arising from the dural tissue encircling the optic nerve, typically arising in the orbital component of the nerve capable of spreading along the nerve to become intracranial and involving the optic chiasm. The latter situation is more common in the context of neurofibromatosis type 2 (NF2) the only know causative association for this disease. ONSM represents only 1-2% of all meningiomas and have as their means of presentation slow deterioration of visual function [1, 2]. In 95%

of cases it is unilateral, and may also be associated with mild retro-orbital headaches and proptosis [3]. The 5% that are bilateral is that group more commonly associated with NF2. Various reports include so called secondary ONSM in which extension along the optic nerve may occur secondarily to origin of the meningioma on the sphenoidal ridge with direct extension via the optic canal into the orbit. In this article the description will only apply to primary ONSM.

As with all meningiomas a typical patient is a female aged between 35 and 60 years of age, with a many month history of visual deterioration [2, 4], although it has been described as occurring in children, in this context behaving in a more aggressive fashion. Diagnosis relies upon formal ophthalmological evaluation with documentation of visual acuity, fundoscopy and perimetry for visual field deficit. In circumstances where the presenting feature is merely visual blurring with retention of acuity, more subtle abnormalities such as colour vision testing and mild dyschromatopsia, and a Marcus Gunn pupil may be the only abnormalities [3]. Limitation of ocular movement is an unlikely occurrence although the presence of proptosis should be considered and assessed. Ocular swelling can occur, and if prolonged can lead to the development of opticociliary shunt vessels on the surface of the disc. Diagnosis is now based on the MR imaging characteristics displaying a thickened optic nerve, with fat suppression views necessary to define the true dimensions of the tumour. Other conditions need to be considered as part of the differential diagnosis [3]. Specific imaging characteristics usually enable separation of the other entities, occasionally a trial of steroids is necessary to exclude the inflammatory conditions that can involve the optic nerve. Schick [1] has described a three tier staging system the differentiating features being the amount of intracranial extension. Type I defines the tumour as being entirely intraorbital, Type II with extension through the optic canal or superior orbital fissure, and Type III has widespread intracranial tumour.

Management has historically been dominated by a form of surgery ranging from biopsy and decompression of the optic nerve to microsurgical resection [1, 2, 4, 5]. The former approach invariably results in progression of the menin-gioma whilst both methods ultimately have a high rate of visual deterioration. Increasingly radiotherapy is regarded as the preferred treatment approach, Carrasco reporting that this 'represents an enormous improvement in a disease entity with typically poor visual prognosis' [5]. Fractionated approaches provide a high opportunity of local control of the tumour plus good prospect of at least visual stabilisation [6-10]. Current stereotactic approaches can dramatically reduce the risk of complications associated with conventional radiotherapy approaches. Thus, the main role for surgery in the future will be for decompression where significant mass effect is evident thus relying upon radiotherapy to control the tumour a feature now applicable to meningiomas at all sites [11, 12].

The aim of this review is to evaluate a single centre's experience with this uncommon tumour across a timeframe where MRI was available for all patients at the time of treatment, and stereotactic irradiation became increasingly the preferred method of treatment.

Materials and Methods

This Ethics approved retrospective study sourced all patients with a diagnosis of meningioma from the clinical database of all patients registered in the Department of Radiation Oncology at Prince of Wales Hospital (POW). 1990 was chosen as a starting point for this review as it was the year that stereotactic radiosurgery (SRS) became available at this facility. Subsequently a specific meningioma database has been established and all tumours coded for sites of involvement. It was thus possible to define origin from the optic nerve, and exclude all those as secondarily involving the optic nerve. February 2004 was the closure point for this study thus allowing for a minimum 18 months of follow up from presentation. Information relating to these patients was obtained from the meningioma database, POW radiotherapy records, referral letters, imaging reports, follow up correspondence from specialists and local medical officers, and if necessary directly with the patient.

Referral was from ophthalmologists or neurosurgeons, with decreased visual acuity in all patients with MRIs to document the extent of disease. Unfortunately the available reports and documentation do not allow categorisation according to the Schick classification.

Treatment techniques evolved over the timeframe of this study as well as being influenced by the treatment aim. In the early years of the study patients were referred with little to no retained vision, and thus the aim was tumour control. Where vision preservation was integral to care, fractionation was used ranging from conventional treatment with 2-3 fields, to stereotactic methods with cones and 'jaws' for pseudo rectangular field shaping, and a MMLC (with 4 mm leaf width collimation) using multiple fixed fields or in intensity modulated radiotherapy (IMRT) mode.

All patients were treated with 6 MeV photons with head fixation appropriate to the treatment method. For the SRS this was with the BRW headframe (Radionics, Burlington, USA), and for fractionated stereotactic it was with the GTC relocatable headframe (Radionics, Burlington, USA). All stereotactic treatments were planned with the same software (Radionics, XKnife, and Xplan) with multiple programme upgrades over the years of the study. This treatment is all given as an outpatient. A consistent rigid quality assurance programme has existed over the timeframe to assure the accuracy and reproducibility of treatment.

Outcomes were measured according to two criteria: radiological assessment of tumour growth, and ophthalmological evaluation of visual acuity and fields. For tumour control this was scored as lack of progression within the volume treated, since many of these patients were treated from other states the follow up reports did not allow sufficient quantification of the amount of reduction to enable tumour decrease to be scored accurately. The report, however, of tumour growth as 'yes or no' was consistent.

In terms of visual evaluation this was rated according to the ophthalmologists reports and the patients more subjective comments. The latter obviously was of more relevance to the patients as it described their day-to-day reaction to treatment. To this extent, visual evaluation was defined as 'no change, better, or worse' noting the timeframe over which this occurred.

Table l. Patient population - Prince of Wales Hospital

Patient numbers

Initial treatment

Recurrent/progression

Gender

Was this article helpful?

0 0

Post a comment