[Alexia without agraphia, colour "agnosia" and right visual field defect: a syndrome of the posterior cerebral artery (author's transl)].

Two cases of alexia without agraphia are reported, with differences in the characters of the alexia and in the accompanying signs. The visual field defect was limited to quadranopia in both cases which was upper quadrantic and mild in one, lower quadrantic and severe in the other. These differences make it unlikely that a similar anatomical location of the lesion and a unique mechanism are responsible of all cases of alexia without agraphia. Persistance of visual inputs in the right visual field is partial in our cases, but alexia without hemianopsia does exist. These facts are against the mechanism of "splenio-cortical" disconnection proposed by Geschwind as the only explanation. A "cortical", or agnosic mechanism has been also claimed, with lesions of the lingual and fusiform gyri on the dominant side, as well as "subangular", mechanism, with intrahemispheric disconnection by a lesion located between the visual associative areas and the angular gyrus: in these last two situations an hemianopsia is not necessarily associated to the alexia without agraphia.