BACKGROUND AND OBJECTIVES: Intraoperative neurophysiological monitoring (IONM), including somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs), aims to reduce ischemic complications during unruptured intracranial aneurysm clipping. This systematic review focuses on the clinical value of IONM. METHODS: We systematically searched PubMed, Medline, and Embase up to January 2025 for studies reporting neurological outcomes after microsurgical clipping of unruptured intracranial aneurysms with IONM. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, outcomes included new neurological deficits at discharge and at first follow-up. In addition to summarizing complication rates across IONM modalities, we conducted an individual patient data analysis to evaluate the predictive value of IONM signal changes. Receiver operating characteristic curve analysis was used to define optimal duration thresholds for reversible IONM changes associated with neurological outcomes. RESULTS: Seventeen studies (3222 patients) were included, with consistent anesthetic protocols, typical demographic characteristics, and modality use aligned with aneurysm location. The individual patient data analysis of 129 cases demonstrated that timely intraoperative intervention in response to IONM signal changes significantly reduces the risk of postoperative neurological deficits. Patients without any IONM signal loss had a 6% deficit rate at discharge. When signal changes occurred, reversal within <18 minutes for MEP or <16 minutes for SSEP was associated with a 15% deficit rate, compared with 95% when signals were not reversed. Isolated changes in either SSEP or MEP also led to deficits, underscoring the added value of multimodal monitoring. CONCLUSION: IONM signal duration and reversibility are critical predictors of neurological outcome in aneurysm surgery. Multimodal IONM not only improves ischemia detection but also offers actionable thresholds for intraoperative decision-making. Its routine use should be considered to reduce neurological morbidity in microsurgical clipping of unruptured aneurysms.
Mirza et al. (2026) studied this question.