Intraoperative use of transcranial motor/sensory evoked potential monitoring in the clipping of intracranial aneurysms: evaluation of false-positive and false-negative cases

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Somatosensory and motor evoked potentials (SEPs and MEPs) are often used to prevent ischemic complications during aneurysm surgeries. However, surgeons often encounter cases with suspicious false-positive and false-negative results from intraoperative evoked potential (EP) monitoring, but the incidence and possible causes for these results are not well established. The aim of this study was to investigate the efficacy and reliability of EP monitoring in the microsurgical treatment of intracranial aneurysms by evaluating false-positive and false-negative cases.


From January 2012 to April 2016, 1514 patients underwent surgery for unruptured intracranial aneurysms (UIAs) with EP monitoring at the authors’ institution. An EP amplitude decrease of 50% or greater compared with the baseline amplitude was defined as a significant EP change. Correlations between immediate postoperative motor weakness and EP monitoring results were retrospectively reviewed. The authors calculated the sensitivity, specificity, and positive and negative predictive values of intraoperative MEP monitoring, as well as the incidence of false-positive and false-negative results.


Eighteen (1.19%) of the 1514 patients had a symptomatic infarction, and 4 (0.26%) had a symptomatic hemorrhage. A total of 15 patients showed motor weakness, with the weakness detected on the immediate postoperative motor function test in 10 of these cases. Fifteen false-positive cases (0.99%) and 8 false-negative cases (0.53%) were reported. Therefore, MEP during UIA surgery resulted in a sensitivity of 0.10, specificity of 0.94, positive predictive value of 0.01, and negative predictive value of 0.99.


Intraoperative EP monitoring has high specificity and negative predictive value. Both false-positive and false-negative findings were present. However, it is likely that a more meticulously designed protocol will make EP monitoring a better surrogate indicator of possible ischemic neurological deficits.

ABBREVIATIONS AChA = anterior choroidal artery; DSA = digital subtraction angiography; EP = evoked potential; GOS = Glasgow Outcome Scale; ICG = indocyanine green; ICH = intracerebral hemorrhage; MEP = motor evoked potential; mRS = modified Rankin Scale; MVD = microvascular Doppler; NMB = neuromuscular blockade; NPV = negative predictive value; PPV = positive predictive value; SAH = subarachnoid hemorrhage; SDH = subdural hemorrhage; SEP = somatosensory evoked potential; UIA = unruptured intracranial aneurysm.

Article Information

Correspondence Wonhyoung Park: University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea.

INCLUDE WHEN CITING Published online March 23, 2018; DOI: 10.3171/2017.8.JNS17791.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.



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    This 71-year-old woman had a 4-mm aneurysm at the origin of AChA (case 7 in Table 4). ICG videoangiography and MVD sonography confirmed the patency of the internal carotid artery and AChA. There was no significant EP change during the operation (A); however, the patient showed grade 4 motor deficits in the right upper and lower extremities. Brain CT scans performed immediately after surgery and 1 day postoperatively revealed nothing abnormal (B), but the patient’s motor weakness did not resolve. Thus, diffusion-weighted imaging was performed 3 days postoperatively and revealed a focal acute infarction at the left anteromedial thalamus (C). However, the AChA was shown to be patent by postoperative DSA immediately following the diffusion-weighted imaging study (D).

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    This 46-year-old woman had a 5.6-mm paraclinoid aneurysm (case 1 in Table 4). During the intradural removal of the anterior clinoid process, the surgical high-speed drill injured the medial temporal lobe. The paraclinoid aneurysm was clipped after the bleeding was brought under control. ICG videoangiography and MVD sonography confirmed the patency of the internal carotid artery and its branches, and there were no significant EP changes observed during surgery (A). However, the patient had grade 4 motor deficits in the left upper and lower extremities with ipsilateral ptosis. Postoperative brain CT revealed an ICH in the temporal lobe and an SAH with midline shift toward the contralateral side (B and C).

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    This 72-year-old woman had a 7.4-mm right AChA aneurysm at the point of branching from the right distal internal carotid artery. Two standard clips were applied, leaving enough space from the AChA, which was severely stenotic. However, one of the aneurysm clips had to be placed over a perforating vessel, as the perforator was severely adhered to the aneurysm dome (A). ICG videoangiography confirmed the patent blood flow of AChA (B). However, the EP amplitude dropped more than 50%, but the EP results soon normalized after release of the previously applied aneurysm clips (C). Thus, the aneurysm was partially clipped to preserve the small perforator (D and E). The remnant aneurysm sac was secured with endovascular coiling. Panels A and D copyright Asan Medical Center. Published with permission. Figure is available in color online only.





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