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The role of conventional external beam radiotherapy in the management of optic nerve sheath meningiomas (ONSM) has been controversial because of limited radiation sensitivity of these tumours and radiation damage to surrounding tissues.1 Recently, in a study of 64 patients with ONSM managed with observation, surgery, radiotherapy, or surgery and radiotherapy, Turbin and colleagues2 found that patients treated by (conventional) radiotherapy alone demonstrated the best long term visual outcome, and suggested fractionated external beam radiation (5000–5500 cGy) as the initial treatment in selected cases, when preservation of visual function is a reasonable goal.
The collateral damage secondary to conventional radiotherapy may be minimised by better focusing and shaping of the radiation beams, as in stereotactic radiotherapy (SRT).3–5 We report on a woman whom we treated with fractionated SRT for a biopsy proved, large ONSM.
In April 2000 a 41 year old woman was referred with a 1 month history of proptosis of her left eye (Fig 1, top left). She had been treated for a presumed orbital “pseudotumour” with oral prednisone (initial dose 90 mg/day) without effect.
At referral, she had no history of diplopia or retrobulbar pain. On examination, the visual acuity (VA) was 1.25 (unaided) of the right eye and 0.8+ (cc S+2) of the left eye. The intraocular pressure was 18 and 21 mm Hg in the right eye and left eye, respectively. There was a left relative afferent pupillary defect (RAPD). The motility of the left eye was slightly restricted in upgaze. The left eye showed mild periocular swelling and conjunctival chemosis. There was 5 mm of left proptosis without upper eyelid retraction or lid lag. Funduscopy of both eyes showed no abnormalities. Visual field testing (Humphrey field analysis (HFA II 750) showed relative scotomas of the left eye, mainly in both lower quadrants. Visual evoked potential (VEP) examination of the left eye showed prolonged latency and decreased amplitudes, suggestive of optic nerve dysfunction.
Orbital MRI (T1 weighted) scans showed a proptosis of the left eye and a large retrobulbar, intraconal mass that stained intensely with gadolineum contrast (Fig 1, bottom left). Computed tomography (CT) imaging also showed an intensely staining retrobulbar tumour without calcifications, that encased and slightly displaced the optic nerve. There was no “tram-tracking” sign or bone involvement. No tumour extension into the optic canal or intracranially was noted. Orbital colour Doppler ultrasound imaging showed a highly vascularised retrobulbar mass with a vertical diameter of at least 25 mm (Fig 2, top left).
Since, on imaging, no evident diagnosis could be made, we decided to perform a biopsy on the lesion through a lateral orbitotomy. At surgery, the tumour was pale and solid. Histopathological examination of the incisional biopsy specimen showed whorls of meningothelial cells, with small nuclei and inconspicuous nucleoli, consistent with a meningioma (Fig 2, bottom).
After surgery we observed the patient for 9 months. During this period her left (corrected) VA deteriorated to 0.2 and her left visual field showed progression of her scotomas. This prompted us to treat her with fractionated SRT in March 2001. The radiation, delivered with a 6 MV linear accelerator (Varian), was given 5 days a week at 1.8 Gy per fraction, with a cumulative dose of 54 Gy. Treatment planning was based on orbital MRI matched with CT scans. A non-invasive stereotactic frame was fixed with an external coordinate system (one isocentre). Target and surrounding tissues at risk were defined as volume of interest on contrast media enhanced T1 weighted MRIs and transferred to CT by the stereotactic localisation technique using a three dimensional planning system (X Plan, Radionics). Portals were optimised using a beam’s eye view technique. Five irregularly shaped non-coplanar beams (arcs) per treatment were used. Beam shaping was done with a mini-multileaf collimator (Radionics). No early complications of the radiation treatment were noted. At 6 months after SRT, the (corrected) VA of her left eye had recovered to 0.8, while no RAPD was observed.
Her periocular swelling had markedly diminished (Fig 1, top right). Compared to previous measurements, the protrusion of the left eye had diminished by 4 mm. Funduscopy, however, showed mild pallor of the left optic nerve head. Visual field testing showed unchanged loss of the left visual field compared to pretreatment values, with a higher foveal threshold. VEP measurements showed improved amplitudes, but prolonged latency compared to previous examination. Orthoptic examination showed ductions similar to those before treatment. Post-treatment MRI revealed a markedly decreased tumour size and a decrease of exophthalmos (Fig 1, bottom right). Colour Doppler ultrasonography showed a decrease in tumour size with markedly diminished vascularisation (Fig 2, top right). At the last follow up visit, 16 months after treatment, her left VA and visual fields were stable.
As in the recent report on a presumed ONSM by Moyer et al,5 fractionated SRT in our biopsy proved case gave a remarkable visual recovery without detectable side effects. Both the size and the blood flow of the tumour regressed within the first 6 months, leading to reduced exophthalmos and periocular swelling. The effect of restored cosmesis was important to this young woman whose main complaint was her unilateral exophthalmos.
Since our follow up is limited to 16 months, no conclusions with regard to long term outcome can be made. More cases of SRT for ONSM need to be studied over a longer period of time to assess the efficacy of this treatment.
This study was presented in part at the 196th Annual Meeting of the Dutch Society of Ophthalmologists, Groningen, the Netherlands, March 2002. The SWOO foundation is kindly acknowledged for financial support.