gms | German Medical Science

Objective: Intra-operative functional mapping and monitoring plays an important role in brain tumor surgery in terms of maximizing the extent of resection (EOR) while minimizing the risk of neurological morbidity. Effective monitoring of optic pathway function, however, is a major challenge. We present first results of our prospective feasibility study on the use of intra-operative visual evoked potentials (VEPs) for eloquent brain tumor surgery.

Methods: Brain tumor patients with critical involvement of posterior optic pathways underwent visual evoked potential (VEP) monitoring during neuronavigated surgical resection. VEPs were generated by a flashing light-emitting device and monitored by scalp electrodes. Moreover, cortical and subcortical VEP recordings were tested using a monopolar probe under diffusion tensor imaging (DTI)-guidance. Extent of resection (EOR) was determined by postoperative magnetic resonance imaging. Patients’ visual function was assessed before and after surgery by standardized visual field and visual acuity testing by a board-certified ophthalmologist.

Results: 18 consecutive patients were included (10 males, median age 63 y). Patients suffered from malignant gliomas (n=11), brain metastases (n=5), pilocytic astrocytoma and hemangiopericytoma (n=1 each). In 12 cases surgery was performed in recurrent disease. Tumors encroached on the distal segment of the optic tract in 3, the Meyer’s loop in 5, the optic radiation in 12, and the visual cortex in 7 patients. Preoperatively 4 patients did not show vision impairment, 10 patients suffered from incomplete visual field deficits and in 4 patients a complete hemianopia was objectified. After surgery visual function improved, remained unchanged or got worse in 6, 9 and 3 patients, respectively. Complete resection was feasible in 14 patients (mean EOR 95%). No postoperative ischemia within optic pathways was seen. VEP monitoring was feasible in all patients with mostly stable latencies and amplitudes. Stable recordings were also obtained by monopolar probes placed within optic pathways surrounding the tumor formation. One patient with loss of intraoperative VEPs developed complete hemianopia postoperatively.

Conclusion: Intraoperative VEP monitoring can serve as a monitoring tool for posterior optic pathways. Electrophysiological data seem to be reproducible and informative during surgery despite high inter-individual variability.