Monitoring of motor evoked potentials compared with somatosensory evoked potentials and microvascular Doppler ultrasonography in cerebral aneurysm surgery

Abstract

Monitoring of MEPs is superior to SSEP monitoring and MDU in detecting motor impairment, particularly that from subcortical ischemia. Microvascular Doppler ultrasonography is superior to EP monitoring in detecting inadvertent vessel occlusion, but cannot assess remote collateral flow. Motor evoked potentials are most sensitive to all other intraoperative conditions and have a direct influence on the course of surgery in the majority of events. A controlled study design is required to confirm the positive effect of monitoring on clinical outcome in aneurysm surgery.

The Incidence of Unacceptable Movement with Motor Evoked Potentials During Craniotomy for Aneurysm Clipping

“…However, they noted that MEPs elicit patient movement, and they emphasized the need for communication to coordinate brief surgical pauses for MEP monitoring to avoid potential movement during microsurgery. Other authors have reported difficulty in consistently obtaining transcranial MEP responses in the lower extremities without using a stimulus intensity that produces unacceptable twitching artifact (6,20); this did not seem to be problematic in our patients.…”

“…It was previously reported that in approximately 6%e10% of patients undergoing transcranial MEP monitoring without neuromuscular blockade, recording was impossible during microsurgery because of electrostimulation-induced muscle contraction or failure to elicit a baseline motor response from muscles that were intact in the preoperative period (20,27). Quiñones-Hinojosa et al (22) reported good success obtaining transcranial MEPs in a small group (N ¼ 30) of patients with aneurysms.…”

“…Too high of a stimulus intensity can activate the deep subcortical motor pathways and bypass higher cortical levels, which can lead to generation of myogenic MEPs from contralateral limbs despite possible cortical ischemia. Subcortical motor pathway ischemia also could be missed if corticospinal tract activation occurred even more caudally (2,5,6,13,20). Transcranial MEPs are made more accurate by decreasing stimulation intensity, and it is recommended that the lowest possible stimulation intensity be used (5,8,20,28).…”

“…Reported morbidity rates for clipping of unruptured aneurysms range from 4%e11% (1). Morbidity is often due to inadvertent ischemic injury from brain retraction, compromise of small perforating arteries during dissection, temporary arterial occlusion, or permanent clips impinging on the parent vessel or perforating arteries (20,24).…”

“…Because MEPs and SEPs provide complementary information about the patient's nervous system, one of these modalities alone might be less likely to reflect the patient's true postoperative neurologic status (30). In up to 25% of cases in which a new postoperative deficit (mostly paresis) manifests, there were unaltered intraoperative SEP recordings; this is likely because the motor pathways derive some blood supply from arteries that are anatomically distinct from arteries supplying sensory cortical pathways (20). In addition, likely owing to differences in the amount of collateral circulation to the vulnerable area, MEP monitoring can give relatively early warning of potential ischemic injury (8,9).…”