視神経を分割していた内頚動脈―眼動脈動脈瘤の1破裂例

A Case of Ruptured Carotid-Ophthalmic Aneurysm Splitting the Optic Nerve

Ⅰ．はじめに

　視神経近傍に発育増大した動脈瘤が視神経を圧迫し，視力視野障害を来す症例は少なからず経験するが，脳動脈瘤が視神経を分割していた状態で破裂した症例は稀である^1,2,5,6)．われわれは，視神経を分割していた内頚－眼動脈動脈瘤の破裂例に遭遇し，この種の動脈瘤では文献的に視力の温存率が低いことから，術中視覚誘発電位（visual evoked potential：VEP）^8,9)を用い視神経の温存を意識しながら手術を施行したので報告する．

　A rare case of ruptured carotid-ophthalmic aneurysm splitting the optic nerve was reported.

　A 52-year-old man presented with a sudden severe headache and bilateral visual deterioration. His right visual acuity was hand motion and the left was 2.0. His left visual field revealed a partial defect of the temporal visual field. Three-dimensional CT angiography revealed an ophthalmic aneurysm of 9 mm projecting superior-medially.

　The operation was performed to preserve the visual function as much as possible. The C2 portion aneurysm splitting the right optic nerve was visible. Before aneurysm clipping, the right anterior clinoid process and optic canal were drilled out to reduce the tension of the optic nerve.

　Intraoperative monitoring of visual evoked potential (VEP) under propofol anesthesia was performed to prevent further visual disturbance. Electroretinogram (ERG) was introduced to ascertain the arrival of the light stimulus at the retina even when the VEP could not be recorded.

　The right ERG was recorded, but the right VEP was flat. Both ERG and VEP were reproducible on the left side. Six months after the operation, the right visual acuity had improved to 0.08 and the visual field revealed nasal hemianopsia. The left visual acuity was unchanged while the visual field had improved to upper temporal quadrant hemianopsia.

　Various attempts to preserve the visual function were discussed.