Optic Nerve Sheath Meningioma

Optic nerve sheath meningiomas (ONSMs) are rare, and usually benign, tumors involving meninges surrounding the optic pathway. They have a higher incidence in middle-aged females. Diagnosis heavily relies on modalities such as magnetic resonance imaging (MRI) and functional imaging (e.g., Ga68DOTA PET). ONSM can be subclassified as primary ONSM (pONSM) and secondary ONSM (sONSM). ONSMs, in general, exhibit slowly progressive enlargement, which invariably leads to visual symptoms and/or vision loss. Although surgery may have a role in sONSMs, it commonly leads to postoperative blindness in pONSMs. Radiotherapy (RT) remains the mainstay of treatment for this condition. Highly conformal RT techniques such as stereotactic fractionated RT (SFRT) have been shown to be effective in retaining functional vision, with low treatment-related morbidity. With standard fractionated doses of 50–54 Gy, almost all patients achieve local control, and 80% or more of patients report vision improvement or stabilization. In this chapter, we will review the clinical findings and the treatment recommendations for this condition.