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Intraoperative neurophysiological monitoring during aneurysm surgery can reduce the risk of ischemic insults and can improve neurological prognoses by detecting abnormal findings in real time when cerebral circulation is at risk. In aneurysm clipping surgery, ischemic insults are most likely to occur at the clipping step. Somatosensory evoked potentials (SSEPs) are known to be the most sensitive method for detecting ischemic insults. However, there are several cases in which SSEP findings and the postoperative prognosis are inconsistent. we report a patient who showed postoperative neurologic deficits after posterior communicating artery (P-com) aneurysm clipping surgery, even though the amplitude of the SSEP had fully recovered shortly after the point at which it had decreased by 15%. The patient's brain MRI revealed an anterior thalamic infarction, and transfemoral cerebral angiography showed an anterior thalamoperforating artery occlusion. This case shows that if a thalamic infarction occurs in the anterior region (not in the posterolateral region, which is involved in the somatosensory pathway), then it may not be identified by SSEP.

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The intraoperative neurophysiological monitoring (INM) during carotid endarterectomy (CEA) can lower the ischemic insult by detecting intracranial hypoperfusion. Two patients with symptomatic or asymptomatic carotid artery stenosis underwent the CEA with INM using somatosensory evoked potential (SSEP), motor evoked potential (MEP), and quantitative electroencephalography (qEEG). We could detect the intracranial hypoperfusion and recommended the carotid shunt. The changes showed in INM were recovered shortly after the carotid shunt was applied. The patients were discharged without any neurologic deterioration. We successfully detected the intracranial hypoperfusion during CEA using the SSEP and the qEEG. The multimodal INM using SSEP, MEP, EEG can selectively screen patients necessary for the carotid shunt during CEA to prevent complications of the surgery.

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