Brain imaging in a patient with hemimicropsia

Hemimicropsia is an isolated misperception of the size of objects in one he mifield (objects appear smaller) which is, as a phenomenon of central origi n, very infrequently reported in literature. We present a case of hemimicro psia as a selective deficit of size and distance perception in the left hem ifield without hemianopsia caused by a cavernous angioma with hemorrhage in the right occipitotemporal area. The symptom occurred only intermittently and was considered the consequence of a local irritation by the hemorrhage. Imaging data including a volume-rendering MR data set of the patient's bra in were transformed to the 3-D stereotactic grid system by Talairach and wa rped to a novel digital 3-D brain atlas. Imaging analysis included function al MRI (fMRI) to analyse the patient's visual cortex areas (mainly V5) in r elation to the localization of the hemangioma to establish physiological la ndmarks with respect to visual stimulation. The lesion was localized in the peripheral visual association cortex, Brodm ann area (BA) 19, adjacent to BA 37, both of which are part of the occipito temporal visual pathway. Additional psychophysical measurements revealed an elevated threshold for perceiving coherent motion, which we relate to a pa rtial loss of function in V5, a region adjacent to the cavernoma. In our study, we localized for the first time a cerebral lesion causing mic ropsia by digital mapping in Talairach space using a 3-D brain atlas and to pologically related it to fMRI data for visual motion. The localization of the brain lesion affecting BA 19 and the occipitotemporal visual pathway is discussed with respect to experimental and case report findings about the neural basis of object size perception. (C) 1999 Elsevier Science Ltd. All rights reserved.