Awake Surgery for Brain Tumors

*Julio Plata-Bello, Helga Fariña-Jerónimo and Yaiza Pérez-Martín*

#### **Abstract**

Surgery is one of the most important steps in most of brain tumors management. In this regard, the extent of resection has been considered as an important prognostic factor. However, the resection may be limited by the presence of functional brain tissue around or in the tumor. Preventing functional damage during brain surgery is essential to keep a good postoperative performance status and for facing the successive steps in brain tumor management (i.e., radio- and/or chemotherapy). This chapter will describe all the procedures around an awake surgery for a brain tumor: from presurgical preparation to postoperative treatments and follow-up. It will not focus only on surgical approaches, but also on the specific aspect of the disciplines that are involved in this procedure.

**Keywords:** brain tumor, awake surgery, intraoperative neuromonitoring

#### **1. Introduction**

Principles of brain tumor surgery consist of the achievement of maximal resection by preserving the function. In this regard, different tools have been developed in the last decades, which help neurosurgeons to achieve that goal. Presurgical functional and anatomical studies, neuronavigation, fluorescence-guided surgery, and intraoperative neurophysiological monitoring (IONM) have become a standard in neuro-oncological surgery.

IONM has not only demonstrated being useful in preserving the function, but also its use is associated with an increase in the extent of resection and an improvement in the quality of life. IONM includes different techniques, and among them, direct cortical and subcortical stimulations in an awake patient are considered as the gold standard for the identification and preservation of functional areas. The information provided by direct cortical and subcortical stimulation in an awake patient cannot be completely substituted by any presurgical imaging or functional study. Therefore, bearing in mind that different complex functions should be preserved to maintain or improve, not only the neurological status, but also the quality of life in each patient, awake surgery for brain tumors is a widespread technique.

This chapter performs a narrative review about awake surgery in brain tumors, addressing the whole procedure (from patient selection to postsurgical rehabilitation) and adding the author's point of view derived from their own experience.

#### **2. Indications of an awake surgery in brain tumor patients**

Awake craniotomy is indicated in any patient with a supratentorial intra-axial lesion adjacent or in eloquent areas, that is, regions with functional importance for the patient, among which, we highlight the motor and language areas. However, there are other functions, relevant and frequently underestimated in patients who are undergoing surgical treatment, such as working memory, attention, mentalizing, semantics [1]. In fact, monitoring during the surgical procedure must be adapted not only to the lesion location, but also to preserve all relevant functions that ensure a good quality of life.

The lesions that are usually operated by awake craniotomy are mainly low- and high-grade gliomas, since in these cases an attempt is made to achieve the maximum tumor resection with the least possible neurological damage (overall survival is related to the extent of tumor resection). However, it is also used in patients with refractory epilepsy, deep brain stimulation, and vascular injury surgery, especially arteriovenous malformations [2].

Regarding glial lesions, there is controversy in the indication of awake surgery in tumor recurrences, but there are several studies that confirm that glioma recurrence surgery does not provide neuropsychological sequelae, since no significant differences are detected in the pre- and post-surgical neuropsychological status of the patient in his/her first- and second-surgery [1].

Until a few years ago, patients with right hemisphere lesions were usually operated under general anesthesia, except if it was necessary to monitor sensorimotor function and motor evoked potentials or somatosensory evoked potentials were not available. However, to maintain the quality of life of brain tumor patients, it is also necessary to preserve other functions (visuospatial function, executive functions such as memory, attention, judgment). For this reason, nowadays the benefit of an awake craniotomy is considered for all patients with a supratentorial glial lesion, regardless of their location (dominant or non-dominant hemisphere).

Therefore, the awake surgery aims to maximize the extent of resection (EOR) but mainly preserve (but not restricted to) the following functions:

**Sensorimotor function.** It is considered when the lesion is located within or adjacent to the perirrollandic cortex, the supplementary motor area, or the corticospinal tract. Direct electrostimulation (DES) has elucidated the complexity and breadth of motor function. The corticospinal tracts present a somatotopic organization, like the supplementary motor network, responsible for stopping or accelerating movement when stimulated in awake patients [3]. Furthermore, there is evidence of bilateral motor responses caused by unilateral subcortical stimulation, which indicates the existence of a wide and complex bilateral cortico-subcortical network that connects premotor areas, basal ganglia, and spinal cord to control bimanual coordination, language, movement, and cognition [4].

Likewise, the use of DES has demonstrated motor interference when stimulating sensitive tracts, probably related to transient inhibition of fibers, indicating the existence of a wide fronto-thalamic-parietal network involved in sensorimotor control [3].

**Visual area.** Direct stimulation of optical radiation can cause a temporary visual field deficit (homonymous hemianopia) if the stimulation is of the fibers that connect with the calcarine fissure, or visual hallucinations if the stimulation is of the fibers that connect with the association visual cortex, involved in visual processing [3].

**Language.** Since the introduction of direct intraoperative cortical and subcortical stimulation, Broca-Wernicke's model ("localizationist model") has been re-evaluated, providing a new model based on the existence of multiple interconnected direct and indirect cortico-subcortical networks involved in phonological, articulatory, syntactic, and semantic processes [5]. Theoretically, there is a dual-flow language model: a ventral pathway (semantics) and a dorsal pathway (phonological and articulatory processes). The dorsal pathway is projected toward the parietal and inferior frontal lobe, involving the superior longitudinal fasciculus (DES) and the arcuate fasciculus (AF) as white matter pathways [6]. During the picture-naming task, the DES of the

#### *Awake Surgery for Brain Tumors DOI: http://dx.doi.org/10.5772/intechopen.101802*

inferior parietal lobe and inferior frontal gyrus is associated with the appearance of phonological paraphasias, while cortical stimulation of the ventral premotor cortex, supramarginal gyrus, and posterior portion of the superior temporal gyrus generates articulatory mistakes. Likewise, AF stimulation causes conduction aphasia and SLF has been implicated in working phonological memory, essential for learning new words and syntactic processing. In the ventral or semantic pathway, one has to consider the role of the inferior fronto-occipital fascicle (IFOF) and an indirect circuit composed of the inferior longitudinal fascicle (ILF), temporal pole, and the uncinate fasciculus (UF). IFOF stimulation during the picture-naming task leads to semantic paraphasias [7] and can also produce verbal perseveration, suggesting a role in semantic control [8]. The indirect circuit (ILF and UF) participates in verbal semantic processing and the posterior portion of the ILF is important for visual recognition and reading [9].

**Others.** Depending on the patient's profile, the cortico-subcortical mapping can be adapted to preserve specific functions that may be associated with the selfperceived quality of life. For example, multi-language mapping and the ability to voluntarily switch languages, mathematical calculation in teachers, music processing and interpretation in musicians, visuospatial perception in dancers, or bimanual coordination in pianists.

### **2.1 Contraindications**

The only absolute contraindication for awake craniotomy is the patient's denial of it. Relative contraindications include the following: neurological causes (severe dysphasia, drowsiness, confusional state, or cognitive disorders that limit patient collaboration); claustrophobia; psychiatric instability; tumor characteristics (large size producing midline displacement >2 cm or highly vascularized lesions); difficulties to control the airway (uncontrollable cough, morbid obesity, obstructive apnea); and medical conditions that associate with high surgical risk and contraindicate any type of neurosurgical intervention. Age is not considered a contraindication for awake craniotomy (ages recorded in the last 10 years range from 9 to 90 years) [1].

#### **2.2 Advantages and disadvantages**

The main objective of glioma surgery is to improve overall survival and quality of life by maximizing tumor resection and it is known that awake surgery, with direct cortical and subcortical electrostimulation, allows locating and protecting the relevant functions for each patient. Thus, greater and safer resection can be achieved, by reducing postoperative sequelae and improving the prognosis.

Awake surgery has been demonstrated to reduce morbidity and mortality, with better control of postsurgical seizures and a higher postsurgical Karnofsky performance status (KPS). All of this leads to a shorter hospital stay and lower healthcare costs.

The main disadvantage that may be associated with awake surgery is the emotional stress for the patient (10–40% of patients experienced anxiety perioperatively) and up to 30% reported pain during the procedure [10].
