Utility of evoked potentials during anterior cerebral artery and anterior communicating artery aneurysm clipping

Abstract

Objective: To investigate the optimal combination of somatosensory- and transcranial motor-evoked potential (SSEP/tcMEP) modalities and monitored extremities during clip reconstruction of aneurysms of the anterior cerebral artery (ACA) and its branches.

Methods: A retrospective review of 104 cases of surgical clipping of ruptured and unruptured aneurysms was performed. SSEP/tcMEP changes and postoperative motor deficits (PMDs) were assessed from upper and lower extremities (UE/LE) to determine the diagnostic accuracy of each modality separately and in combination.

Results: PMDs were reported in 9 of 104 patients; 7 LE and 8 UE (3.6% of 415 extremities). Evoked potential (EP) monitoring failed to predict a PMD in 8 extremities (1.9%). Seven of 8 false negatives had subarachnoid hemorrhage. Sensitivity and specificity in LE were 50% and 97% for tcMEP, 71% and 98% for SSEP, and 83% and 98% for dual-monitoring of both tcMEP/SSEP. Sensitivity and specificity in UE were 38% and 99% for tcMEP, and 50% and 97% for tcMEP/SSEP, respectively.

Conclusions: Combined tcMEP/SSEP is more accurate than single-modality monitoring for LE but is relatively insensitive for UE PMDs.

Significance: During ACA aneurysm clipping, multiple factors may confound the ability of EP monitoring to predict PMDs, especially brachiofacial hemiparesis caused by perforator insufficiency.

Keywords: ACA, anterior cerebral artery; ACoA, anterior communicating artery; Anterior cerebral artery; Anterior communicating artery; Cerebral aneurysm; EP, evoked potential; IONM, intraoperative neurophysiological monitoring; Intraoperative neurophysiological monitoring; MCA, middle cerebral artery; MEP, motor-evoked potential; Motor-evoked potential; RAH, recurrent artery of Heubner; SSEP, somatosensory-evoked potential; Somatosensory-evoked potential; tcMEP, transcranial motor-evoked potential.

Fig. 1

Left and right transcranial motor-evoked potential (tcMEP) monitoring during clipping of an anterior communicating artery aneurysm. (Case Nr 112) A) After the clip was applied at 12:47, tcMEP waveforms were preserved in all four extremities (blue arrows). B) At 1:00 pm, a decline in the right foot signal was noted (red arrow) that triggered an alert and the clip was removed by the surgeon. C) Three minutes later, the polyphasic response was regained (green arrow). (Display gain: 100 microV/division, time base: 10 msec/division). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

A schematic illustration of blood supply of the internal capsule. The recurrent artery of Heubner supplies the anterior genu, which typically houses corticospinal tract fibers corresponding to the upper extremity and face. Reprinted from Textbook of Clinical Neuroanatomy, 2nd ed., Singh V (ed.), Fig. 14.12, 2010, with permission from Elsevier.