[Continuous monitoring of cortical visual evoked potentials by means of subdural electrodes in surgery on the posterior optic pathway. A case report and review of the literature].

INTRODUCTION

Intraoperative monitoring of functional language and motor areas is a commonly used technique which makes it possible to minimise the post-operative sequelae and to perform an optimal resection of lesions in these areas. Monitoring of the visual cortex, however, is not usually carried out nowadays. The scarce spatial resolution and its sensitivity to anaesthesia are some of the technical difficulties that reduce its clinical usefulness. The study reports a case of resection of an occipital lesion under general anaesthetic, with intraoperative monitoring of the cortical visual evoked potentials (VEP) by means of subdural electrodes.

CASE REPORT

A 50-year-old female who underwent surgery involving the resection of an occipital lesion that was suggestive of radionecrosis. The VEP were monitored by administering flashing light at 4.1 Hz and recording with subdural strip electrodes on the occipital cortex. During the operation, a progressive lowering of the amplitude of the cortical VEP was observed when 50% of the baseline amplitude was exceeded, and thus the resection was finished. The increase in latency was below 10% of the baseline value. The patient recovered well during the post-operative period and her sight did not present any changes with respect to the baseline values.

CONCLUSIONS

In our case, monitoring the cortical VEP by cortical recordings produced stable recordings with a good correlation with the post-operative visual function. Cortical recordings performed either directly or by means of subdural electrodes make it possible to achieve adequate spatial resolution and response intensity. Further studies need to be conducted with a greater number of patients in order to obtain decisive conclusions.