Review
Is a wake-up call in order? Review of the evidence for awake craniotomy

https://doi.org/10.1016/j.jocn.2015.11.004Get rights and content

Highlights

  • Awake craniotomy (AC) has been reported chiefly for resection of low grade gliomas.

  • AC enables function preservation when resecting tumors in eloquent areas.

  • Successful mapping and localization of function improves preservation of function.

  • Preservation of complex function is best in experienced referral centers.

  • AC is not consistent in its effect on extent of resection.

Abstract

Awake craniotomy (AC) has been used in increasing frequency in the past few decades. It has mainly been used for resection of intrinsic tumors, but also, rarely, for other pathologies. The vast majority of reports specific to one pathology, however, have focused on resection of low grade glioma in the awake setting. Tumors in eloquent areas have mainly been resected when the patient is awake for the purpose of preservation of function. Motor function is the most documented, and most successfully preserved function. Other functions are harder to localize with direct electrical stimulation (DES), and thus more difficult to preserve. The success rate of DES localization correlates to the rate of function preservation. The effect of AC on extent of resection is inconsistent in the literature. Other functions, such as sensory and visuospatial recognition, have been protected during AC, but this is best performed in large, referral centers that have experience with the procedure. Other benefits to AC, such as cost-effectiveness and reduction in patient pain and anxiety, have also been reported.

Introduction

Awake craniotomy (AC) has been used for resection of a wide variety of pathologies [1], [2], [3], [4]. Its use has expanded significantly over the last decades [2], [5], [6], [7], and both the indications and techniques are continuously evolving. AC has been utilized for resection of vascular lesions, epileptic foci, and rarely, extrinsic brain tumors [3], [8], [9], [10], [11], but the main role for AC has been for resection of intrinsic brain tumors, mainly low grade glioma (LGG), high grade glioma (HGG) and cerebral metastases.

Many reasons to undertake craniotomies in the awake setting have been quoted in the literature, of which the most important is the potential to decrease the likelihood of injury to eloquent areas of the brain. An AC enables the surgeon to monitor the function of a center, or tract, during an awake resection which, in turn, is thought to decrease the likelihood of a new neurological deficit or worsening of an existing deficit following the resective operation. The second reason to perform a craniotomy in the awake setting is the potential for an increased extent of resection (EOR), because of the increased confidence in the safety of the resection provided by the awake monitoring. Other advantages of an AC when compared to a craniotomy under general anesthesia (GA) are the reduced cost of functional monitoring compared to continuous neurophysiological monitoring.

In this article we review the available literature, and discuss evidence for any of the advantages described. The review will focus on the clinical controversies surrounding AC, including evidence of benefit for the different tumor pathologies resected in the awake setting, the effect an awake resection might have on the EOR, and the evidence for preservation of various functions in AC. Finally, we will consider other advantages for resection with an AC.

Section snippets

Which tumors should be resected using an AC?

The majority of the data available in the literature is related to resection of primary brain tumors. To our knowledge, there has been no report of a series – neither retrospective nor prospective – of AC used for the exclusive resection of metastases.

Furthermore, although there have been case series reports [12], [13], [14], [15], there has also been no series limited to HGG resection in AC, to our knowledge. Many authors have reported on unselected cohorts of primary brain tumors or intrinsic

Does AC affect EOR?

The main purpose of AC is preservation of function in eloquent brain areas during tumor resection. The effect AC has on the EOR is unclear. It may be hypothesized that the awake setting would limit the ability to continue the resection after the point of neurological deficit, even if that deficit would eventually recover, and the EOR would thus be lower. However, the opposite may also be stipulated: perhaps areas of tumor that would not be explored in the asleep setting, due to potential

What functions can be preserved with AC?

The main functions that have been protected with AC are language or motor ability.

In regard to the ease at which one function is protected compared to other functions, Kim et al. reviewed 309 consecutive patients who were operated awake for removal of intraaxial tumors [42]. Of these, 73% were HGG, 19% were LGG and the rest were other pathologies, including metastasis, infection and others. Regarding the ability to map successfully and to localize the brain area responsible for the function

What other advantages are there for AC?

As described earlier, the two main advantages of AC are preservation of function and planning of a safe maximal resection. As we have shown, the evidence for preservation of function is quite persuasive, but it cannot be concluded decisively that awake resection improves or worsens the EOR. Several other measures were assessed in AC compared to craniotomy under GA.

Summary

AC is mainly used and reported for resection of LGG. The reported effect of AC on EOR is not consistent. AC is mainly used for preservation of motor function and speech preservation, but at times also for preservation of other functions. It may be concluded that localization of function on DES is associated with better preservation of function. Overall, motor function is most likely to be localized and therefore better preserved. Other functions, requiring more complex assessment, such as

Conflicts of Interest/Disclosures

The authors declare that they have no financial or other conflicts of interest in relation to this research and its publication.

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