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抄録 中脳梗塞による動眼神経部分麻癖例を経験したので報告する。症例51歳男性。朝起床後複視にて発症した。神経学的には,軽度の右片麻痺,右知覚鈍麻,小脳症状を一過性に示した。特徴的なのは,眼球運動筋麻痺型の動眼神経の部分麻痺であり,6カ月後も持続していた。CT上,左中脳被蓋と左視床前内方に低吸収域を有しており,脳底動脈分岐部の傍正中穿通枝閉塞によるlacunar infarctと診断した。この中脳部の梗塞巣が,動眼神経麻痺の責任病巣と思われた。従来は,動眼神経の部分麻痺の原因として髄外の圧迫性および虚血性病変が強調されているが,本症例より,中脳の限局性病巣でも生じうることが明らかとなった。人の中脳病巣による動眼神経部分麻痺の発生機序に関する解剖には不明な点が多いが,Warwickの動眼神経核内のsubnucleusのtopographyは参考になる。この症例にみられた眼球運動筋麻痺型は,神経繊維が被蓋傍正中部で横に広がった部分の最外側の病巣でおきやすいと考えられる。また動眼神経繊維の上下の広がりにより,中脳上部傍正中部の病巣でlevator sparing型,下部の病巣でpupil sparingが両側性にそれぞれ生じることが文献的にも認められた。
A case of partial oculomotor palsy due to mid-brain infarction is reported.
Case presentation : Fifty-one-year old man noted a sudden onset of double vision. He transiently presented right hemiparesis, right hemihypesthe-sia and cerebellar ataxia. The main symptom was the left oculomotor palsy selectively involving extraocular muscles (levator and pupil sparing), lasting for more than 6 months.
The CT scan showed localized and well demar-cated low-density areas at the left tegmentum of midbrain and left anteromedial thalamus, diag-nosed as lacunar infarction due to occulusion of paramedian perforators at the basilar bifurcation. This midbrain infarct was supposed to be re-sponsible for the partial oculomotor palsy.
Extramedullary compressive and ischemic lesions have been well-known main causes of partial oculo-motor palsy. This case, however, has empha-sized the importance of recognition of midbrain lesion as a causative location of the partial oculo-motor palsy.
While the anatomical elucidation of this infre-quent palsy is not sufficient, a topography of oculomotor nuclear complex in rhesus monkey proposed by Warwick, is worthwhile to correlate with midbrain oculomotor palsy in human cases. The pupil and levator sparing oculomotor palsy is most frequently caused by the laterally loca-lized lesion at the fascicular portion which ex-tends transversely at the midbrain tegmentum. This is the most likely lesion in this reported case.
It is reported, on the other hand, that the levator sparing type oculomotor palsy is caused by a paramedian lesion of rostral midbrain and pupil sparing type by caudal midbrain. These may be explainable by rostro-caudal extension of the nuclear complex.
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