[A case of visual allesthesia].

A case of visual allesthesia is reported. A thirty-year-old right-handed man with a right temporo-occipital arteriovenous malformation underwent the surgery for extirpation of the lesion. Postoperatively he had left homonymous hemianopsia. Approximately 6 months after the surgery, he experienced the initial spell of generalized convulsion, followed by the episodes of visual allesthesia. He experienced illusory left hemonymous transpositions of objects viewed in the right homonymous field. The transposition occurred 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.