Intraoperative oculomotor nerve monitoring predicts outcome following clipping of posterior communicating artery aneurysms.

Valid parameters do not exist to predict oculomotor nerve palsy (ONP, ptosis and/or diplopia) intraoperatively. In 49 operations involving 46 patients with posterior communicating artery aneurysms, the oculomotor nerves were stimulated after the aneurysms were clipped. A quantitative analysis of evoked compound muscle action potential (CMAP) parameters (stimulus threshold, amplitude and latency) from the levator palpebrae superioris (LPS) muscle was performed. Absolute values of CMAP amplitude statistically correlated with initial and long-term oculomotor nerve function (ONF) after surgery (p<0.05). In addition, subarachnoid hemorrhage (SAH) significantly influenced the CMAP threshold (p<0.05). Monitoring of LPS muscle activity is valuable in the assessment of ONF, and the CMAP amplitude of LPS may be a reliable predictor of ONF. Moreover, SAH has an impact on the parameters of the LPS CMAP.