Multichannel visual evoked potentials in the assessment of visual pathways in children with marked brain abnormalities

Abstract

To demonstrate how multichannel visual evoked potentials (VEPs) can provide quantitative measures of visual function in children with marked cortical anatomy abnormalities. Four children with marked brain pathology (2 holoprosencephaly, 2 giant interhemispheric cysts with hydrocephalus) underwent pattern reversal and flash VEP recordings from 16 equally distributed electrodes. Voltage maps of the major VEP components were constructed, and their distributions were compared to the magnetic resonance imaging (MRI) findings. No reproducible responses were evident in 1 case, and responses were present, but, as expected based on the MRI finding, not over the occipital electrodes in 3 cases. Thus, the standard clinical VEP electrode placement would not have detected responses. The distribution of responses during monocular testing obtained in 2 cases suggested normal decussation of the visual pathways at the chiasm, and voltage mapping indicated which part of the abnormally positioned brain tissue is functional visual cortex. In children with markedly abnormal brain anatomy, multichannel VEP recordings can provide quantifiable measures of visual pathway function detected in atypical locations. VEPs provide a quantifiable measure of visual function that could be used to assist in determining visual acuity levels, and offered a baseline for monitoring in the context of raised intracranial pressure. These recordings were also able to identify functional anatomical structures that were not apparent on MRI. In a clinical setting, the use of additional recordings from nonstandard electrode placement based on the MRI findings is suggested.