外転神経麻痺を発症した未破裂巨大脳底動脈瘤の1例

Abducens nerve palsy in a case with unruptured giant vertebrobasilar aneurysm

要約　目的：外転神経麻痺を契機として発見された未破裂巨大脳底動脈瘤の症例の報告。

症例：62歳の男性が1年前からの右方視時の複視で紹介受診した。40年前に外斜視の手術を受け，6年前に高血圧と診断された。

所見と経過：矯正視力は左右眼ともに1.0で，右眼に−2D，左眼に−1Dの近視があった。眼位は近視で6Δ，遠見で正面と左方視で4Δの外斜位，右方視で25Δの内斜視があり，右眼に外転制限があった。単純CTで右橋部に径25mmの塊があり，MRIで橋部の塊内部は等または低信号，MRAでこの塊は脳底動脈の前方にあり，脳底動脈とともに右方に偏位していた。椎骨血管造影で動脈瘤への血液流入はなく，内部が血栓化した未破裂巨大脳底動脈瘤と診断した。以後11か月間の保存的治療で所見に著変はない。

結論：脳底動脈の巨大動脈瘤は，頻度は低いが外転神経麻痺の原因となりうる。

Abstract　Purpose: To report a case of abducens nerve palsy that led to detection of unruptured giant vertebrobasilar anrurysm.

Case: A 62-year-old male was referred to us for diplopia when looking to the right since one year before. He had received surgery for exotropia 40 years before. He had been diagnosed with systemic hypertension 6 years before.

Findings and Clinical Course: Corrected visual acuity was 1.0 in either eye. The right eye was myopic by −2D. The left eye was myopic by −1D. The eye position was exophoric by 6Δ for near and by 4Δ for distance. Esotropia by 25Δ developed when looking to the right. Simple computed tomography（CT）showed a mass with the diameter of 25 mm in the pons. Manetic resonance imaging（MRI）and angiography（MRA）showed the mass to be thrombosed aneurysm in the basilar artery. The aneurysm was slightly dislocated to the right. There has been no radical changes in the findings during the follow-up for 11 months.

Conclusion: This case illustrates that unruptured giant aneurysm in the basilar artery may cause ipsilateral abducens nerve palsy.