Visual allesthesiaの一例

A Case of Visual Allesthesia

　右側頭—後頭移行部脳動静脈奇形の摘出術後，visuai allesthesiaを来した症例を報告する。患者は脳内出血で発症した右利き30歳男性で，手術後の神経学的脱落症状としてほぼ完全な左同名半盲を認めた。抗てんかん薬の服用にもかかわらず術後6カ月にて全身性けいれんを来し，その直後に右同名視野でみた視覚像が数秒後，左同名視野に転移，復活し，さらにその像が数分間保続すると訴えた。この訴えは数日後には消失した。この症候はvisual ailesthesiaと考えられ，転移像はpalinopticである。転移像は実像と同様鮮明であり単眼でもみられた。転移の方向は健常側から障害側に向い，従来の広範な大脳病変あるいは精神障害に伴う報告とは逆であり，また完全な同名半盲に伴う例は稀である。MRIにより病変は，外側は右側頭葉中および下側頭回から後頭葉，一部頭頂葉皮質を含み，内側面は側頭—後頭移行部，fusiform gyrusからlingual gyrusにかけて，両葉の連絡を絶つように存在し，さらに外側膝状体から視床後半部に達していた。全身性けいれんの直後に一過性に生じたことから，メカニズムとして刺激性病変の関与が示唆された。

A case of visual allesthesia is reported.

A thirty-year-old right-handed man with a right temporo-occipital arteriovenous malformation under-went the surgery for extirpation of the lesion.

Postoperatively he had left homonymous hemianop-sia. Approximately 6 months after the surgery, he expe-rienced the initial spell of generalized convulsion, foll-owed by the episodes of visual allesthesia. He experi-enced illusory left hemonymous transpositions of objects viewed in the right homonymous field. The transposition occured from normal to the defective visual field.

The illusory image was palinoptic, persisting for up to several minutes after the real object was no longer in view. It was equal in shape with the original, and caused monocular diplopia.

MRI showed a large area of postoperative changes. The lesion was located from the posterior half of the middle and inferior gyri of the right temporal lobe to the occipital and a part of the parietal cortex. And it extended into the right fusiform and lingual gyri. The right lateral geniculate body and the posterior part of thalamus were also involved.

We speculated that this phenomenon may result from irritation of the affected brain and its surrounding areas, since the episode took place following the seizure.