Latency-shift of intra-operative visual evoked potential predicts reversible homonymous hemianopia after intra-ventricular meningioma surgery

OBJECTIVES: Intraoperative visual evoked potentials (VEPs) are used to monitor the function of optic radiation during neurosurgery with the P100 amplitude decrement as a predictor of post-operative visual deficit. However, there is currently no evidence of early VEP changes indicating reversible visual field affection. METHODS: In this case report, we used VEPs during surgery for a benign meningioma located in the atrium of the right lateral ventricle. The tumor was accessed through a transcortical approach via a two-centimeter corticotomy in the lateral aspect of the superior parietal lobule. We performed flash VEPs and simultaneous recordings of electroretinography alongside with multimodal intraoperative monitoring. RESULTS: We observed a significant and sustained unilateral latency shift of the P100 component of VEPs, while amplitudes temporarily dropped to 80% of baseline but recovered entirely at the end of surgery. After the operation, the patient had a left-sided lower-quadrant anopia, which recovered completely during the following three months. Diagnostic VEP with pattern reversal monocular full field stimulation at one month postoperatively showed normal latencies bilaterally. CONCLUSION: Our case indicates that the VEP (P100) latency may be a new and valuable indicator (in addition to VEP amplitude) of the visual pathways. SIGNIFICANCE: Monitoring VEPs may be useful to detect an imminent injury and a potentially reversible functional deficit.