Excerpt
It seems that the total resection of low-grade gliomas extends both the overall and tumor-free survival in most patients. However, of course, since the prognosis of these patients also depends on their functional state, the threat of loss of function caused by an operation and their quality of life must be considered. In his review, Duffau [
1] claims that awake surgery is the method of choice to extend the survival, preserve the quality of life, and thus is unequivocally needed in most, if not all, of these tumors. We totally agree with him that only differentiated pre- and postoperative neuropsychological testing will reveal minor deficits that are not at all recognized during a routine clinical examination and are frequently not even noted by their patients. We also agree that neurological deficits can be avoided by awake craniotomy with intraoperative cortical and subcortical stimulations and electrophysiological recordings. However, as useful as awake craniotomy is, it carries several problems. It requires a dedicated neurosurgical team and experienced neuroanaesthetist that are willing to cooperate with the surgeon and electrophysiologist. Massive brain herniation, coughing of the patient during surgery, and particularly intraoperative convulsions in an awake patient are nightmares of almost any neurosurgeon. There are measures to eliminate this potential problem, such as preoperative treatment with corticosteroids and mannitol, respiratory care, and rinsing the cortex with cold Ringer solution if seizures occur [
2]. However, particularly for those who do not deal every day with awake patients, the situations are not easy to manage. Furthermore, there are patients who are in no way ideal candidates for this technique, such as individuals with cognitive failures, dementia, and those with psychiatric problems. Duffau [
1] does very unfortunately not even mention these drawbacks and the availability of an alternative strategy, which is preoperative functional determination of cortical areas related to motion, sensation, speech, and vision and their respective tract connections. They attribute a longer survival to more radical tumor resection, but awake craniotomy, even if it can preserve neurological function, does actually not contribute to more radical tumor excision. However, intraoperative MR imaging may be utilized as an excellent tool to ascertain utmost possible tumor resection. Frequently the delineation of a low-grade glioma as revealed particularly by T2-weighted and FLAIR MR sequences is more precise than the surgeon is able to visualize the tumor margins and residual tissue by visible light, even if his perception is enhanced by an excellent operating microscope. Whether the pathological tissue has all been extracted can thus be most reliably documented by intraoperative MR investigations, particularly if high field systems are used. Frequently, residual tumor can be identified intraoperatively and the resection can be completed, unless functional navigation, which very precisely delineates the cortical areas and fiber tracts, prevents the extension of abnormal tissue resection. This includes preservation of the visual pathways. The neurosurgeon gets an almost online feedback on what he has achieved during the resection which is not only a perfect quality control but also accelerates the learning curve of those who just acquire glioma surgery techniques. The much-feared brain shift can be intraoperatively compensated by re-adjustments of neuronavigation, based on the images obtained after partial tumor resection [
3]. Thus, one would have to rephrase the question that Duffau [
1] posed just as “is it against the current state of art to practice surgery of adult supratentorial low-grade gliomas without intraoperative MR imaging?” Several studies have shown the benefit of intraoperative MR imaging: the percentages of additional tissue resections and the much higher total extent of tumor resection, which plays a pivotal role, particularly in low-grade gliomas were convincingly demonstrated, irrespective of whether low [
4,
5] or high field systems were used for intraoperative imaging [
3,
6,
7]. Awake craniotomy can help to preserve neurological functions, but we question that differentiated neuropsychological testing is possible intraoperatively, as the patient is exposed to much distress. In contrast, in the relaxed preoperative functional investigation, in which time is not a critical issue, differentiated testing is performed easily and the preoperatively obtained dataset of function in the navigation can be easily matched with the intraoperative structural recordings [
3]. Fiber tracks can be recognized by DTI MR imaging pre- or intraoperatively and can be precisely visualized. The patient can thus be tested in a much superior fashion [
3]. However, we admit that not each and every patient is suitable to undergo the sophisticated paradigms that are required for proper testing. However, many do and provide perfect datasets for intraoperative functional navigation. We are surprised that the concept of awake craniotomy and intraoperative imaging together were applied in a few patients, for which also intraoperative functional neuronavigation based on preoperative acquired data was available, which is a maximal expenditure that is certainly not available at each and every place of this planet [
8] and might even be addressed as “technical overkill”. Many patients still will have to undergo surgery without all this enormous technical support. Those, who have tumors adjacent to functional areas, however, should be referred to centers, in which at least one of the mentioned technologies [
1,
6,
9] is available. …
