Introduction Optic Nerve Sheath Meningiomas (ONSMs) are rare tumours. They represent approximately the 2% of all orbital tumours, 1-2% of intracranial meningiomas and one third of the optic nerve lesions (23, 32, 42, 43). Usually these tumour are monolateral but 5% have a bilateral development (33) On the base of the growth pattern these tumours can be classified in primary and secondary forms. The former type arise from the arachnoid cap cell of the fibrous dural capsule of the optic nerve and they usually growth circumferentially along the nerve. Primary ONSMs can be further subdivided in orbital and intracanalicular forms.