gms | German Medical Science

Objective: Intraoperative monitoring (IOM) of visual evoked potentials (VEP) during anterior skull base surgery may be challenging, predominately due to varying methodological approaches or technical difficulties. This results in heterogeneous data regarding the ultimate sensitivity and surgical benefit of intraoperative monitoring of VEP. We aimed to demonstrate the feasibility of intraoperative monitoring of VEPs and to identify its clinical benefits and limitations.

Methods: From October 2015 to September 2016, 12 patients (9 women and 3 men) underwent optic nerve decompression for sphenoid wing meningeomas which compromised or compressed the anterior visual pathway (optic nerve and/or chiasm) at our department. Following total intravenous anesthesia, VEP recordings were obtained through flash light stimuli delivered directly over a closed eyelid during surgery. Additionally, we performed electroretinography (ERG) recordings to confirm successful retinal activation during stimuli. We collected data on the surgical procedure, preoperative and postoperative visual function, VEP P100 features, and changes of VEP and ERG before, during and at the end of the surgery.

Results: All patients underwent optic nerve decompression and/or radiologically complete tumor resection in case of unilateral location or ipsilateral complete resection in case of bilateral presentation. One patient underwent a redo craniotomy due to early tumor recurrence in a grade 2 meningeoma. VEP recordings were feasible and reliable in 20 (77%) out of 26 examined eyes. VEP recordings of the remaining six (23%) eyes were not possible due to severe preoperative visual impairment. All patients had recordable ERG. After frontal scalp-flap reflection, of the nine ipsilateral eyes with recordable VEP, five (56%) experienced complete disappearance and four (44%) had significant changes. All previously lost or significantly altered VEP and ERG responses except one returned to baseline during skin-flap closure.

Conclusion: Intraoperative VEP monitoring is sensitive to detect intraoperative deterioration of visual function due to surgical dissection but it also correlates with preoperative visual function, which limits the additive value of VEP monitoring in severely impaired patients. However, ERG monitoring is a useful tool to distinguish technical (light axis deviation) from functional VEP variances. Skin-flap mobilization and reflection is a common cause of technical VEP lost due light axis deviation requiring a more reliable method to fix and ensure VEP monitoring.