Optic nerve sheath meningioma: diagnostic features and therapeutic alternatives.

Twenty-two cases of optic nerve sheath meningioma were reviewed. The clinical features included slowly progressive visual loss in every case. Orbital signs of limited ocular movements and mild proptosis were present in only a third of cases; gaze-evoked amaurosis occurred in 3 cases. The disc was abnormal in every case, usually swollen if vision was 6/12 or better, atrophic if the vision worse than 6/12. Optociliary shunt vessels occurred in 5 patients and were of diagnostic significance. The diagnosis was made by a high-resolution CT scan of the orbits showing tubular expansion of the optic nerve sheath. Calcification of the optic nerve was present in 12 cases. Tubular expansion of the optic nerve sheath may occur in raised intracranial pressure, optic nerve glioma, granuloma, lymphoma or metastatic disease. In the absence of calcification these alternative diagnoses must be considered. Surgery, undertaken for the intracranial component of the tumour, did not halt progressive visual loss.