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Optic nerve sheath meningioma
Optic nerve sheath meningiomas (ONSM) are rare benign tumors of the optic nerve. 60–70% of cases occur in middle age females, and is more common in older adults (mean age 44.7 years). It is also seen in children, but this is rare. The tumors grow from cells that surround the optic nerve, and as the tumor grows, it compresses the optic nerve. This causes loss of vision in the affected eye. Rarely, it may affect both eyes at the same time.
It is typically a slow growing tumor, and has never been reported to cause death. However, there is concern that the tumor can grow into the brain and cause other types of neurological damage. In some patients, the tumor grows so slowly that treatment is not necessary. Standard treatments are observation, surgery, radiation therapy, and combinations of the above.〔
==Incidence==
About 1–2% of all meningiomas are optic nerve sheath meningiomas. Meningiomas have an incidence of ~4.18/100,000 persons each year. Thus, ~10,000 meningiomas are diagnosed in the US each year; corresponding to ~100 cases of ONSM each year in the US. The actual number of meningiomas is likely much higher as it is very common in elderly women. ONSM comprises about 2% of orbital tumors, and about 10% of optic nerve lesions.
Neurofibromatosis type II (NF-2) affects around 9% of ONSM patients, where the incidence in the general population is around 0.03–0.05%. Thus NF-2 is felt to be a risk factor for the development of ONSM.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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