gms | German Medical Science

Objective: Despite to importance of the monitoring of the visual system during surgery for brain lesions, there is a lack of successful intraoperative application reports of visual evoked potentials (VEP), and the published results are very controversial. In this study we report our experience of VEP during surgery.

Method: Since the introduction of intraoperative VEP monitoring in our clinic we investigated 30 patients. In the last 20 cases, included in this study, Intraoperative VEP was done bilaterally using optic stimulation of each eye separately with LED goggles and recording bilaterally from O1 and O2 scalp electrodes in International 10-20 system. All patients underwent magnetic resonance imaging (MRI) pre- and postoperatively including diffusion tensor tractography (DTI). Patients underwent selective amygdalohypocampektomy for hippocampal sclerosis (n=7), lesionectomy and temporal lobe resection in case of epileptogenic lesions of the temporal lobe (n=4), temporal lobe resection for tumour removal (n=3), and functional hemispherotomy because of intractable epilepsy by Rassmussen encephalitis (n=2). Surgery was performed using neuronavigation with reconstructed DTI of the visual pathway. Postoperative evaluation included clinical and computerized visual field (CVF) investigations by ophthalmologists and MRI with DTI of the visual pathway.

Results: Successful intraoperative recording of VEPs was achieved in 16 of the 20 (80%) patients. Postoperative visual field deficit was documented in 9 of the 16 patients (56%), 3 patients with homonymous hemianopsia, and 6 patients with contralateral upper quadrantanopsia. All patients with postoperative homonymous hemianopsia had intraoperative flattening of the ipsilateral VEP curves. The lesions to the visual pathway were confirmed using postoperative DTI tractography. In 2 of the 6 patients with postoperative quadrantanopsia we detected significant decrease of the VEP amplitudes. In 4 cases of postoperative quadrantanopsia we noticed no changes in VEP, in these patients the deficit was not noticed by patients but by CVF investigations.

Conclusions: After a learning curve, VEP can be recorded under general anesthesia in most of the cases showing good feasibility and reproducibility. VEP changes were good predicting hemianopsia but with low sensitivity for quadrantanopsia in this small study. Improvement in stimulation or recording specificity to detect lesions in postchiasmatic fibers is the object of future investigations.