Intraoperative neurophysiological monitoring of extracranial-intracranial bypass procedures

Clinical article

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Intraoperative neurophysiological monitoring (IONM) represents an established tool in neurosurgery to increase patient safety. Its application, however, is controversial. Its use has been described as helpful in avoiding neurological deterioration during intracranial aneurysm surgery. Its impact on extracranial-intracranial (EC-IC) bypass surgery involving parent artery occlusion for the treatment of complex aneurysms has not yet been studied. The authors therefore sought to evaluate the effects of IONM on patient safety, the surgeon's intraoperative strategies, and functional outcome of patients after cerebral bypass surgery. Intraoperative neurophysiological monitoring results were compared with those of intraoperative blood flow monitoring to assess bypass graft perfusion.


Compound motor action potentials (CMAPs) were generated using transcranial electrical stimulation in patients undergoing EC-IC bypass surgery. Preoperative and postoperative motor function was analyzed. To assess graft function, intraoperative flowmetry and indocyanine green fluorescence angiography were performed. Special care was taken to compare the relevance of electrophysiological and blood flow monitoring in the detection of critical intraoperative ischemic episodes.


The study included 31 patients with 31 aneurysms and 1 bilateral occlusion of the internal carotid arteries, undergoing 32 EC-IC bypass surgeries in which radial artery or saphenous vein grafts were used. In 11 cases, 15 CMAP events were observed, helping the surgeon to determine the source of deterioration and to react to it: 14 were reversible and only 1 showed no recovery. In all cases, blood flow monitoring showed good perfusion of the bypass grafts. There were no false-negative results in this series. New postoperative motor deficits were transient in 1 case, permanent in 1 case, and not present in all other cases.


Intraoperative neurophysiological monitoring is a helpful tool for continuous functional monitoring of patients undergoing large-caliber vessel EC-IC bypass surgery. The authors' results suggest that continuous neurophysiological monitoring during EC-IC bypass surgery has relevant advantages over flow-oriented monitoring techniques such as intraoperative flowmetry or indocyanine green–based angiography.

Abbreviations used in this paper:CMAP = compound motor action potential; EC-IC = extracranial-intracranial; ELANA = excimer laser-assisted nonocclusive anastomosis; ICA = internal carotid artery; ICG = indocyanine green; IOF = intraoperative flowmetry; IONM = intraoperative neurophysiological monitoring; SSEP = somatosensory evoked potentials; TCES = transcranial electrical stimulation.

Article Information

Address correspondence to: Julius Dengler, M.D., Department of Neurosurgery, Charité-Universitätsmedizin Berlin, Campus Virchow Klinikum, Augustenburger Platz 1, Berlin 13353, Germany. email:

Please include this information when citing this paper: published online May 10, 2013; DOI: 10.3171/2013.4.JNS122205.

© AANS, except where prohibited by US copyright law.



  • View in gallery

    T2-weighted MR image (A) and left ICA angiogram (anteroposterior view) (B) of a left giant fusiform M2/3 aneurysm. Waveform (C) of CMAPs recorded from the right thenar muscle during temporary clipping of an M3 branch distal to a left giant fusiform M2/3 aneurysm. The action potentials were stable throughout the surgical procedure.

  • View in gallery

    T2-weighted MR image (A) and left ICA angiogram (oblique view) (B) of a left giant fusiform cavernous ICA aneurysm. Waveform (C) of CMAP development after temporary clip application to a left M2 branch. The amplitude decreases (single arrow) and the latency increases (triple arrow) after application of the clip. CMAPs recover after removal of the clip (double arrow).

  • View in gallery

    Graph showing 5 cases of CMAP events during proximal or distal aneurysm occlusion. The columns indicate the latency of the occurrence of a CMAP event after clip occlusion (left), the time span until clip removal (center), and time span until CMAP recovery (right). Values are given as the mean × SD.


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