Functional evaluation using magnetic resonance imaging of the visual cortex in patients with retrochiasmatic lesions

Object. The goal of this study was to evaluate the clinical potential of co mbining functional magnetic resonance (fMR) imaging with conventional morph ological MR imaging and to assess its usefulness for objective evaluation o f visual function as part of treatment planning in patients harboring space -occupying lesions involving the posterior afferent visual system. Methods. It was hypothesized that regional activation of the visual cortex during visual stimulation would show an asymmetric response consistent with the well-known retinotopical organization of the human visual cortex. To t est this hypothesis, the pattern of regional cortical activity detected by fMR imaging during binocular repetitive photic stimulation (10 Hz) was comp ared with the findings of conventional visual field testing. Functional map ping of the visual cortex was performed using a noninvasive blood oxygen le vel-dependent MR technique in 10 patients with intraaxial and two with extr aaxial lesions. Experiments involving two of the patients were unsuccessful because of motion artifacts. In all the remaining patients functional acti vity was demonstrated in the primary visual area that corresponded to the a natomical location of the calcarine cortex. In nine patients, the identifie d patterns of activation in the visual cortex were consistent with the visu al field deficits (seven homonymous hemianopsias, one homonymous central sc otoma, and one inferior quadrantanopsia) and with the traditional teaching of retinotopical representation. Discordance between fMR imaging and perime tric findings was observed in one case. Conclusions. These results demonstrate that fMR imaging can be performed ro utinely and successfully in patients with visual abnormalities as part of a conventional neuroradiological evaluation. The technique provides essentia l information about the function-structure relationship specific to an indi vidual patient and holds promise not only for diagnosis and therapy plannin g, but also for understandings the topography and functional specialization of the human visual cortex.