gms | German Medical Science

Objective: Intraoperative neuromonitoring (IOM), particularly somatosensory evoked potentials (SEP) and motor evoked potentials (MEP) evolved as standard of care in a variety of neurosurgical procedures. However, impact of IOM on outcome of elective microsurgical clipping of unruptured intracranial aneurysms (EC-UIA) is yet unknown. Our aim was to retrospectively analyze the neurological outcome before and after IOM introduction for EC-UIA at our neurovascular center and to evaluate it regarding feasibility and clinical impact.

Methods: Patients undergoing EC-UIA were included from 2007 until 2014. IOM was introduced starting 2011 and was routinely conducted in all cases by properly trained technicians. For median and tibial nerve SEP and extremity muscle MEP monitoring, cut-off criteria for abnormality were defined as amplitude diminishment of > 50%. MEP stimulation was bihemispheric and suprathreshold. Procedures before (136 procedures, NIOM-group) and after introduction of IOM (138 procedures, IOM-group) were analysed regarding SEP/MEP changes and neurological outcome.

Results: Both groups did not significantly differ in sex distribution, risk factors, aneurysm diameter and location. Median follow-up was 3 months (IOM-group) and 6 months (NIOM-group) respectively (p < 0.001). Age was higher in the IOM-group (57 vs. 54yrs., p = 0.01). In the IOM-group, SEPs were obtained in 138 cases (100%), MEPs in 137 cases (99%). IOM showed significant changes in 18 cases, 4 of which exhibited postoperative hemisyndrome (true-positive cases). 12 patients showed no new deficits, 1 each suffered from ataxia and coma. Those 14 cases were defined as false-positives and were not included in risk stratification, since they cannot be detected by SEP/MEP monitoring. 5 patients with new hemisyndrome did not meet cut-off SEP/MEP alterations (false-negative cases). Sensitivity of SEP/MEP monitoring was 44%, specificity 89%, positive predictive value 22%, negative predictive value 89%. False-positive rate was 11%, false-negative rate was 56%. In the IOM-group, there were 18 new postoperative deficits (13%; 4.3% permanent), 9 of which affecting pathways covered by SEP/MEP (hemisyndrome), 9 not detectable (cranial nerve deficits, seizures, ataxia, coma). In the NIOM-group there were 19 new deficits (14%; 6% permanent, including 7 hemisyndromes). The groups neither significantly differed in count (p = 0.093) and nature (p = 0.832) of postoperative deficits nor in their recovery-rate (p = 0.169).

Conclusion: Introduction of SEP/MEP monitoring did not affect overall neurological outcome in EC-UIA at our department due to a low sensitivity and high false-negative rate. Considering the low risk profile in most clipping procedures and complications, principally undetectable by SEP/MEP-monitoring, future studies should address IOM-vindicating risk factors, as well as modified IOM techniques.