Low-threshold monopolar motor mapping for resection of lesions in motor eloquent areas in children and adolescents

Awake craniotomy in pediatric low-grade glioma: barriers and future directions

INTRODUCTION

The goal of surgical management in pediatric low-grade gliomas (pLGGs) is gross total resection (GTR), as it is considered curative with favorable long-term outcomes. Achieving GTR can be challenging in the setting of eloquent-region gliomas, in which resection may increase risk of neurological deficits. Awake craniotomy (AC) with intraoperative neurofunctional mapping (IONM) offers a promising approach to achieve maximal resection while preserving neurological function. However, its adoption in pediatric cases has been hindered, and barriers to its adoption have not previously been elucidated.

FINDINGS

This review includes two complementary investigations. First, a survey study was conducted querying pediatric neurosurgeons on their perceived barriers to the procedure in children with pLGG. Next, these critical barriers were analyzed in the context of existing literature. These barriers included the lack of standardized IONM techniques for children, inadequate surgical and anesthesia experience, concerns regarding increased complication risks, doubts about children's ability to tolerate the procedure, and perceived non-indications due to alternative monitoring tools.

CONCLUSION

Efforts to overcome these barriers include standardizing IONM protocols, refining anesthesia management, enhancing patient preparation strategies, and challenging entrenched beliefs about pediatric AC. Collaborative interdisciplinary efforts and further studies are needed to establish safety guidelines and broaden the application of AC, ultimately improving outcomes for children with pLGG.

Intraoperative neurophysiological monitoring in paediatric neurosurgery

Intraoperative neurophysiological monitoring (IONM) is commonly used in various surgical procedures in adults, but with technological and anaesthetic advancements, its use has extended to the paediatric population. The use of IONM in children poses a unique set of challenges considering the anatomical and physiological differences in this group of patients. The use of IONM aids in the localization of neural structures and enables surgeons to preserve the functional neural structures leading to decreased incidence of postoperative neurological deficits and better patient outcomes. In this article, we review the use of IONM in paediatric patients undergoing various spinal and cranial neurosurgical procedures. We discuss the patient characteristics, type of surgeries, and technical and anaesthetic considerations about IONM in this population.

Intraoperative mapping of pre-central motor cortex and subcortex: a proposal for supplemental cortical and novel subcortical maps to Penfield's motor homunculus

Penfield’s motor homunculus describes a caricaturised yet useful representation of the map of various body parts on the pre-central cortex. We propose a supplemental map of the clinically represented areas of human body in pre-central cortex and a novel subcortical corticospinal tract map. We believe this knowledge is essential for safe surgery in patients with eloquent brain lesions. A single-institution retrospective cohort study of patients who underwent craniotomy for motor eloquent lesions with intraoperative motor neuromonitoring (cortical and subcortical) between 2015 and 2020 was performed. All positive cortical and subcortical stimulation points were taken into account and cartographic maps were produced to demonstrate cortical and subcortical areas of motor representation and their configuration. A literature review in PubMed was performed. One hundred and eighty consecutive patients (58.4% male, 41.6% female) were included in the study with 81.6% asleep and 18.4% awake craniotomies for motor eloquent lesions (gliomas 80.7%, metastases 13.8%) with intraoperative cortical and subcortical motor mapping. Based on the data, we propose a supplemental clinical cortical and a novel subcortical motor map to the original Penfield’s motor homunculus, including demonstration of localisation of intercostal muscles both in the cortex and subcortex which has not been previously described. The supplementary clinical cortical and novel subcortical motor maps of the homunculus presented here have been derived from a large cohort of patients undergoing direct cortical and subcortical brain mapping. The information will have direct relevance for improving the safety and outcome of patients undergoing resection of motor eloquent brain lesions.

Technical Considerations in Awake Craniotomy with Cortical and Subcortical Motor Mapping in Preadolescents: Pushing the Envelope

INTRODUCTION

Unlike adult gliomas, the utility of combined application of awake anesthesia and intraoperative neurophysiological monitoring (IONM) for maximal safe resection in eloquent region gliomas (ERG) has not been established for pediatric population while it remains unexplored in preadolescents (below 11 years old).

CASE PRESENTATION

We report 2 cases of awake craniotomy with IONM in an 8 and 9 year old for safe maximal resection of ERG. In both the cases, repeated preoperative visits of the operating room was performed to familiarize and educate the children about intraoperative communication, comfortable positioning, and neurological assessment. Under conscious sedation protocol, cortical and subcortical mapping, and electrocorticography, gross total resection was achieved. In both the cases, there were no postoperative neurodeficits or perioperative complications.

CONCLUSION

Our 2 cases illustrate the first instance of successful use of awake IONM for maximal safe resection of ERG in preadolescent age-group. We believe, with proper preoperative planning and careful titration of anesthetics, it is safe and feasible. The blanket notion that preadolescent age-group should be excluded from awake mapping needs to be challenged, rather curated on a case basis.

Mapping of the Motor Cortex

The resection of brain tumors located within or near the eloquent tissue has a higher risk of postoperative neurological deficits. The primary concerns include loss of sensory and motor functions in the contralateral face, upper and lower extremities, as well as speech deficits. Intraoperative neurophysiological monitoring (IONM) techniques are performed routinely for the identification and preservation of the functional integrity of the eloquent brain areas during neurosurgical procedures. The IONM modalities involve sensory, motor, and language mapping, which helps in the identification of the boundaries of these areas during surgical resection. Cortical motor Mapping (CmM) technique is considered as a gold-standard technique for mapping of the brain. We present the intraoperative CmM technique, including anesthesia recommendations, types of electrodes, as well as stimulation and recording parameters for successful monitoring.

Electrical Cortical Stimulation: Mapping for Function and Seizures

Surgical procedures for the treatment of epilepsy and brain tumors can involve resection of regions closed or merged to functionally eloquent cortical areas. Removal of language, primary motor, or sensory areas can be associated with transient or permanent functional deficits, which should be avoided if possible. Functional electrical cortical stimulation is a reliable technique to prevent or minimize motor, sensory and language deficits and has been used in humans since the 1950s to identify functional cortex, and it can also localize epileptogenic regions. This article discusses functional electrical stimulation in adults and children for different functional modalities.

Intraoperative Generalized Tonic-Clonic Seizure and Consequent Severe Brain Bulge During Functional Motor Cortex Mapping: A Case Report

Intraoperative cortical and subcortical bipolar or monopolar mapping is the gold standard for neurosurgical procedures that involve lesions near functional or "eloquent" cortex. However, the classic Penfield stimulation has a higher intraoperative seizure rate than high-frequency short-train stimulation. As a result, high-frequency monopolar stimulation is now the most widely practiced technique. However, seizure-free mapping cannot be guaranteed even with high-frequency stimulation particularly at high current thresholds. We encountered a case of severe generalized tonic-clonic seizure and consequent severe brain bulge in an 8-year-old child during cortical mapping with the high-frequency protocol.

Electrical Stimulation Mapping of the Brain: Basic Principles and Emerging Alternatives

The application of electrical stimulation mapping (ESM) of the brain for clinical use is approximating a century. Despite this long-standing history, the value of ESM for guiding surgical resections and sparing eloquent cortex is documented largely by small retrospective studies, and ESM protocols are largely inherited and lack standardization. Although models are imperfect and mechanisms are complex, the probabilistic causality of ESM has guaranteed its perpetuation into the 21st century. At present, electrical stimulation of cortical tissue is being revisited for network connectivity. In addition, noninvasive and passive mapping techniques are rapidly evolving to complement and potentially replace ESM in specific clinical situations. Lesional and epilepsy neurosurgery cases now offer different opportunities for multimodal functional assessments.

Epilepsy surgery near or in eloquent cortex in children-Practice patterns and recommendations for minimizing and reporting deficits

OBJECTIVE

We aimed to investigate the current practices guiding surgical resection strategies involving epileptogenic zones (EZs) near or in eloquent cortex (EC) at pediatric epilepsy surgery centers worldwide.

METHODS

A survey was conducted among 40 respondents from 33 pediatric epilepsy surgery centers worldwide on the weight assigned to diagnostic tests used to define the EZ and EC, how EC is viewed, and how surgeries are planned for foci near or in eloquent cortex.

RESULTS

A descriptive analysis was performed that revealed considerable variation in the use of diagnostic tests and resective strategies toward EZ and EC.

SIGNIFICANCE

The wide variation in strategies may contribute to undesirable outcomes characterized by poor seizure control with added deficits and underscores the need to establish best practices in pediatric epilepsy surgery. The survey data were used to formulate a set of recommendations to help minimize deficits and to report them consistently.

Endoscopic management of a low-grade thalamic glioma: a safe alternative to open microsurgery?

BACKGROUND

Despite considerable advances in preoperative and intraoperative imaging and neuronavigation, resection of thalamic gliomas remains challenging. Although both endoscopic biopsy and third ventriculostomy (ETV) for the treatment of secondary hydrocephalus are commonly performed, endoscopic resection of thalamic gliomas has been very sparsely described.

METHOD

We report and illustrate the surgical procedure and patient's outcome after full endoscopic resection of a thalamic glioma and to discuss this approach as an alternative to open microsurgery.

RESULTS

In 2016, a 56-year-old woman presented with disorientation, dysphasia and right facial hypaesthesia in our department. Cranial magnetic resonance imaging revealed a left thalamic lesion and subsequent hydrocephalus. Initially, hydrocephalus was treated by ETV but forceps biopsy was not diagnostic. However, metabolism in ¹⁸F-fluoroethyl-L-tyrosine positron emission tomography indicated glioma. Subsequently, endoscopic and neuronavigation-guided tumour resection was performed using a <1 cm², trans-sulcal approach through the left posterior horn of the lateral ventricle. While visibility was poor using the intraoperative microscope, neuroendoscopy provided excellent visualisation and allowed safe tumour debulking. Neither haemorrhage from the tumour or collapse of the cavity compromised endoscopic resection.

CONCLUSIONS

In accordance with one previously published case of endoscopic resection of a thalamic glioma, no surgery-related complications were observed. Although this remains to be determined in larger series, endoscopic resection of these lesions might be a safe and feasible alternative to biopsy or open surgery. Future studies should also aim to identify patients specifically eligible for these approaches.

Intra-operative neurophysiological mapping and monitoring during brain tumour surgery in children: an update

INTRODUCTION

Over the past decade, the reluctance to operate in eloquent brain areas has been reconsidered in the light of the advent of new peri-operative functional neuroimaging techniques and new evidence from neuro-oncology. To maximise tumour resection while minimising morbidity should be the goal of brain surgery in children as much as it is in adults, and preservation of brain functions is critical in the light of the increased survival and the expectations in terms of quality of life.

DISCUSSION

Intra-operative neurophysiology is the gold standard to localise and preserve brain functions during surgery and is increasingly used in paediatric neurosurgery. Yet, the developing nervous system has peculiar characteristics in terms of anatomical and physiological maturation, and some technical aspects need to be tailored for its use in children, especially in infants. This paper will review the most recent advances in the field of intra-operative neurophysiology (ION) techniques during brain surgery, focussing on those aspects that are relevant to the paediatric neurosurgery practice.