Optic Nerve Sheath Meningiomas

Optic nerve sheath meningiomas usually do not require biopsy for diagnosis if the typical clinical and radiographic features are present.53,58 Figure 7.9 shows a typical sheath meningioma on Tl-weighted post-contrast fat suppressed MR scan of the orbit. Observation for progression is a reasonable first step in management. Complete surgical excision usually produces irreversible visual loss and is generally reserved for eyes without visual potential and vision-threatening or cosmetically unacceptable proptosis. Observation is an acceptable protocol to evaluate progression with serial neuroimaging (e.g., MRI head and orbits with gadolinium and fat suppression) every 6 months for 2 years, then yearly if there is no growth. Most authors would consider radiation therapy to be the treatment of choice for optic nerve sheath meningioma if preservation of visual function is the goal.48 Improved techniques of delivery of radiotherapy (e.g., conformal,

FIGURE 7.9. Axial fat-suppressed Tl-weighted postgadolinium MR scan of the orbit shows a left enhancing optic nerve sheath meningioma.

three dimensional, intensity-modulated, radiotherapy) may decrease the risks of radiation side effects.52,54

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