[A case of falcotentorial meningioma with visual allesthesia]

Visual allesthesia, in which visual images are transposed from one homonymous half-field of visual field to another, is a rare phenomenon. Palinopsia is the persistence or recurrence of visual images after the exciting stimulus object has been removed. Some authors have reported these phenomena, but these pathophysiology has not been understood. We report a right-handed 63-year-old woman, with a right falcotentorial meningioma. She paroxysmally experienced illusory transpositions of objects viewed in the right homonymous visual field into the left, and she recognized her face in it. The illusory images were palinoptic, persisting for up to a few minutes after the real objects were no longer in view. Administration of anticonvulsant medications resulted in the decrease of frequency of this phenomenon. Radiological and surgical findings revealed that the tumor was compressing the very localized visual cortex, especially the Brodmann's area 18 and 19. After resection of the tumor, visual allesthesia and palinopsia completely disappeared. These areas are associated with memory and recognition of visual images as visuopsychic area. This case provides some insight into the mechanisms of this phenomenon, and we consider that it could be caused by seizure activity in this lesion.