Transcranial motor evoked potential monitoring during the surgical clipping of unruptured intracranial aneurysms
Introduction
Because aneurysm surgery always poses potential risks of ischemic complications, continuous somatosensory evoked potential (SSEP) monitoring has been adopted to identify patients with impending ischemia early during surgery, to enable the surgeon to react in time. However, SSEP monitoring cannot detect isolated damage to structures outside the lemniscal system, at least in theory. Thus, a significant rate up to 10% of cases with new postoperative motor deficits has been observed after surgery for anterior circulation aneurysms, despite unaltered intraoperative SSEP recordings [1], [2], [3], [4].
Consequently, the need for monitoring of the motor pathway was raised and several former studies demonstrated the feasibility of motor evoked potential (MEP) monitoring during aneurysm surgery either elicited by transcranial [3], [5], [6] or direct cortical stimulation [7], [8], [9]. On the basis of MEP changes, the surgeon was able to take corrective measures (e.g. release the clip or retractor blade), which could lead to recovery of deteriorated MEPs in many instances. In some situations, however, the patients suffered hemiparesis despite unchanged or fully recovered MEPs [3], [5], [6], [7], [8], [9]. Thus, the reliability of MEP monitoring is still in doubt. Besides, its impact on the motor outcome has never been studied apart from the enormous effects of subarachnoid and intracerebral hemorrhages. The inclusion of the ruptured cases possibly obscures the surgical results by means of vasospasm, pre-existing hemiparesis, uneven clinical grades, difficulties in exposure and dissection, premature rupture and so on.
We compared motor outcomes before and after the application of transcranial MEP monitoring for a one year period. Only unruptured aneurysms were enrolled in this study population and motor outcomes were correlated with the relevant MEP changes to assess the positive and negative predictive values in a prospective observational design.
Section snippets
Patient population
This study covered the period from January 2007 to December 2008. Transcranial MEP monitoring together with SSEP has routinely been performed for aneurysm surgery in our institute since mid-December 2007. There were only two exceptional cases treated without MEPs monitoring after that, which were operated on an emergent basis. Ruptured cases and aneurysms located in the posterior circulation were excluded to eliminate the effects of hemorrhages and different surgical approaches. Also, cases
Results
Demographic and angiographic profiles are summarized in Table 1. The number of cases treated under MEP monitoring increased. This reflects a recent tendency that surgery for unruptured aneurysms is increasingly performed, in combination with our own policy, which favors open surgery of middle cerebral artery (MCA) aneurysms over endovascular coiling. Nevertheless, no statistical difference was demonstrated between the two cohorts (each p value > 0.5).
In the former surgical cohort, a new
Impact of MEP monitoring on motor outcomes
Aneurysm surgery always poses potential risks of ischemic complications, which encompass unintentional vessel occlusion by the permanent clip, temporary occlusion for proximal control, iatrogenic vasospasm or thromboembolism by surgical manipulation, small vessel injury during dissection, and local ischemia during brain retraction [10], [11], [12]. Thus, even for unruptured aneurysms located in the anterior circulation, the risk of a new postoperative motor deficit still exists in approximately
Conclusions
Transcranial MEP monitoring is a simple, safe, and reliable tool for the prediction of postoperative motor functions. The ischemic complications can be reduced via prompt corrective measures taken on the basis of MEP changes during aneurysm surgery.
Conflicts of interest
We have no conflicts of interest to disclose.
Financial disclosure
We have nothing to declare.
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2020, Clinical Neurology and NeurosurgeryCitation Excerpt :Indeed, the goal of clipping is to exclude the aneurysm saving the patency of parent and perforating arteries to avoid ischemic brain injuries. In this regard, the reported mortality rate of unruptured aneurysms ranges between 0.4 % and 1.5 %, and the mortality rate of ruptured aneurysms is up to 50 % [1–4]. Morbidity rates of microsurgery for unruptured intracranial aneurysms range from 2.2 % to 21.0 %, and new motor deficit related to ischemic complications is reported up to 7.6 % [3].
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2019, Clinical Neurology and NeurosurgeryCitation Excerpt :Especially, IONM detects insufficient blood flow quantitatively during an aneurysm surgery. The efficacy of IONM has been reported in several studies; IONM using SSEPs and MEPs had higher diagnostic accuracy in predicting blood flow insufficiency [13,17,28]. Therefore, it is considered a useful and reliable tool to prevent postoperative ischemic complications.