Pathogenic RHEB Somatic Variant in a Child With Tuberous Sclerosis Complex Without Pathogenic Variants in TSC1 or TSC2.

OBJECTIVE: To describe a child meeting diagnostic criteria for tuberous sclerosis complex (TSC) carrying a pathogenic somatic variant in RHEB, but no pathogenic variants in the 2 known TSC genes, TSC1 or TSC2. METHODS: We present the clinical and imaging findings in a child presenting with drug-resistant focal seizures and multiple cortical tubers, a subependymal giant cell astrocytoma and multiple subependymal nodules in 1 cerebral hemisphere. Targeted panel sequencing and exome sequencing were performed on genomic DNA derived from blood and resected tuber tissue. RESULTS: The child satisfied clinical diagnostic criteria for TSC, having 3 major features, only 2 of which are required for diagnosis. Genetic testing did not identify pathogenic variants or copy number variations in TSC1 or TSC2 but identified a pathogenic somatic RHEB variant (NM_005614.4:c.104_105delACinsTA [p.Tyr35Leu]) in the cortical tuber. DISCUSSION: RHEB is a partner of the TSC1/2 complex in the mechanistic target of rapamycin pathway. Somatic variants in RHEB are associated with focal cortical dysplasia and hemimegalencephaly. We propose that variants in RHEB may explain some of the genetically undiagnosed TSC cases and may be the third gene for TSC, or TSC3.

Basal ganglia dysplasia and mTORopathy: A potential cause of postoperative seizures in focal cortical dysplasia.

Pathogenic somatic MTOR variants in the cerebral cortex are a frequent cause of focal cortical dysplasia (FCD). We describe a child with drug and surgery-resistant focal epilepsy due to FCD type II who developed progressive enlargement and T2 signal hyperintensity in the ipsilateral caudate and lentiform nuclei. Histopathology of caudate nucleus biopsies showed dysmorphic neurons, similar to those in resected cortex. Genetic analysis of frontal and temporal cortex and caudate nucleus identified a pathogenic somatic MTOR variant [NM_004958.4:c.4375G > C (p.Ala1459Pro)] that was not present in blood-derived gDNA. The mean variant allele frequency ranged from 0.4% to 3.2% in cerebral cortex and up to 5.4% in the caudate nucleus. The basal ganglia abnormalities suggest more widespread, potentially hemispheric dysplasia in this patient, consistent with the pathogenic variant occurring in early cerebral development. This finding provides a potential explanation for persistent seizures in some patients with seemingly complete resection of FCD or disconnection of a dysplastic hemisphere.

Karawun: a software package for assisting evaluation of advances in multimodal imaging for neurosurgical planning and intraoperative neuronavigation.

PURPOSE: The neuroimaging research community-which includes a broad range of scientific, medical, statistical, and engineering disciplines-has developed many tools to advance our knowledge of brain structure, function, development, aging, and disease. Past research efforts have clearly shaped clinical practice. However, translation of new methodologies into clinical practice is challenging. Anything that can reduce these barriers has the potential to improve the rate at which research outcomes can contribute to clinical practice. In this article, we introduce Karawun, a file format conversion tool, that has become a key part of our work in translating advances in diffusion imaging acquisition and analysis into neurosurgical practice at our institution. METHODS: Karawun links analysis workflows created using open-source neuroimaging software, to Brainlab (Brainlab AG, Munich, Germany), a commercially available surgical planning and navigation suite. Karawun achieves this using DICOM standards supporting representation of 3D structures, including tractography streamlines, and thus offers far more than traditional screenshot or color overlay approaches. RESULTS: We show that neurosurgical planning data, created from multimodal imaging data using analysis methods implemented in open-source research software, can be imported into Brainlab. The datasets can be manipulated as if they were created by Brainlab, including 3D visualizations of white matter tracts and other objects. CONCLUSION: Clinicians can explore and interact with the results of research neuroimaging pipelines using familiar tools within their standard clinical workflow, understand the impact of the new methods on their practice and provide feedback to methods developers. This capability has been important to the translation of advanced analysis techniques into practice at our institution.

Assessment of intraoperative diffusion EPI distortion and its impact on estimation of supratentorial white matter tract positions in pediatric epilepsy surgery.

The effectiveness of correcting diffusion Echo Planar Imaging (EPI) distortion and its impact on tractography reconstruction have not been adequately investigated in the intraoperative MRI setting, particularly for High Angular Resolution Diffusion Imaging (HARDI) acquisition. In this study, we evaluated the effectiveness of EPI distortion correction using 27 legacy intraoperative HARDI datasets over two consecutive surgical time points, acquired without reverse phase-encoded data, from 17 children who underwent epilepsy surgery at our institution. The data was processed with EPI distortion correction using the Synb0-Disco technique (Schilling et al., 2019) and without distortion correction. The corrected and uncorrected b0 diffusion-weighted images (DWI) were first compared visually. The mutual information indices between the original T1-weighted images and the fractional anisotropy images derived from corrected and uncorrected DWI were used to quantify the effect of distortion correction. Sixty-four white matter tracts were segmented from each dataset, using a deep-learning based automated tractography algorithm for the purpose of a standardized and unbiased evaluation. Displacement was calculated between tracts generated before and after distortion correction. The tracts were grouped based on their principal morphological orientations to investigate whether the effects of EPI distortion vary with tract orientation. Group differences in tract distortion were investigated both globally, and regionally with respect to proximity to the resecting lesion in the operative hemisphere. Qualitatively, we observed notable improvement in the corrected diffusion images, over the typically affected brain regions near skull-base air sinuses, and correction of additional distortion unique to intraoperative open cranium images, particularly over the resection site. This improvement was supported quantitatively, as mutual information indices between the FA and T1-weighted images were significantly greater after the correction, compared to before the correction. Maximum tract displacement between the corrected and uncorrected data, was in the range of 7.5 to 10.0 mm, a magnitude that would challenge the safety resection margin typically tolerated for tractography-informed surgical guidance. This was particularly relevant for tracts oriented partially or fully in-line with the acquired diffusion phase-encoded direction. Portions of these tracts passing close to the resection site demonstrated significantly greater magnitude of displacement, compared to portions of tracts remote from the resection site in the operative hemisphere. Our findings have direct clinical implication on the accuracy of intraoperative tractography-informed image guidance and emphasize the need to develop a distortion correction technique with feasible intraoperative processing time.

Intraoperative magnetic resonance imaging in epilepsy surgery: A systematic review and meta-analysis.

This systematic review investigated the added value of intraoperative magnetic resonance imaging (iMRI)-guidance in epilepsy surgery, compared to conventional non-iMRI surgery, with respect to the rate of gross total resection (GTR), postoperative seizure freedom, neurological deficits, non-neurological complications and reoperations. A comprehensive literature search was conducted using Medline, Embase, PubMed, and Cochrane Reviews databases. Randomized control trials, case control or cohort studies, and surgical case series published from January 1993 to February 2021 that reported on iMRI-guided epilepsy surgery outcomes for either adults or children were eligible for inclusion. Studies comparing iMRI-guided epilepsy surgery to non-iMRI surgery controls were selected for meta-analysis using random-effects models. Forty-two studies matched the selection criteria and were used for qualitative synthesis and ten of these were suitable for meta-analysis. Overall, studies included various 0.2-3.0 Tesla iMRI systems, contained small numbers with heterogenous clinical characteristics, utilized subjective GTR reporting, and had variable follow-up durations. Meta-analysis demonstrated that the use of iMRI-guidance led to statistically significant higher rates of GTR (RR = 1.31 [95% CI = 1.10-1.57]) and seizure freedom (RR = 1.44 [95% CI = 1.12-1.84]), but this was undermined by moderate to significant statistical heterogeneity between studies (I2 = 55% and I2 = 71% respectively). Currently, there is only level III-2 evidence supporting the use of iMRI-guidance over conventional non-iMRI epilepsy surgery, with respect to the studied outcomes.

One-Stage, Limited-Resection Epilepsy Surgery for Bottom-of-Sulcus Dysplasia.

OBJECTIVE: To determine whether 1-stage, limited corticectomy controls seizures in patients with MRI-positive, bottom-of-sulcus dysplasia (BOSD). METHODS: We reviewed clinical, neuroimaging, electrocorticography (ECoG), operative, and histopathology findings in consecutively operated patients with drug-resistant focal epilepsy and MRI-positive BOSD, all of whom underwent corticectomy guided by MRI and ECoG. RESULTS: Thirty-eight patients with a median age at surgery of 10.2 (interquartile range [IQR] 6.0-14.1) years were included. BOSDs involved eloquent cortex in 15 patients. Eighty-seven percent of patients had rhythmic spiking on preresection ECoG. Rhythmic spiking was present in 22 of 24 patients studied with combined depth and surface electrodes, being limited to the dysplastic sulcus in 7 and involving the dysplastic sulcus and gyral crown in 15. Sixty-eight percent of resections were limited to the dysplastic sulcus, leaving the gyral crown. Histopathology was focal cortical dysplasia (FCD) type IIb in 29 patients and FCDIIa in 9. Dysmorphic neurons were present in the bottom of the sulcus but not the top or the gyral crown in 17 of 22 patients. Six (16%) patients required reoperation for postoperative seizures and residual dysplasia; reoperation was not correlated with ECoG, neuroimaging, or histologic abnormalities in the gyral crown. At a median 6.3 (IQR 4.8-9.9) years of follow-up, 33 (87%) patients are seizure-free, 31 off antiseizure medication. CONCLUSION: BOSD can be safely and effectively resected with MRI and ECoG guidance, corticectomy potentially being limited to the dysplastic sulcus, without need for intracranial EEG monitoring and functional mapping. CLASSIFICATION OF EVIDENCE: This study provides Class IV evidence that 1-stage, limited corticectomy for BOSD is safe and effective for control of seizures.

Rationale, design, and methods of a randomized, controlled, open-label clinical trial with open-label extension to investigate the safety of vosoritide in infants, and young children with achondroplasia at risk of requiring cervicomedullary decompression surgery.

Achondroplasia causes narrowing of the foramen magnum and the spinal canal leading to increased mortality due to cervicomedullary compression in infants and significant morbidity due to spinal stenosis later in adulthood. Vosoritide is a C-natriuretic peptide analogue that has been shown to improve endochondral ossification in children with achondroplasia. The objective of this trial is to evaluate the safety of vosoritide and whether vosoritide can improve the growth of the foramen magnum and spinal canal in children that may require decompression surgery. An Achondroplasia Foramen Magnum Score will be used to identify infants at risk of requiring decompression surgery. This is a 2-year open label randomized controlled trial of vosoritide in infants with achondroplasia ages 0 to ≤12 months. Approximately 20 infants will be randomized 1:1 to either open label once daily subcutaneous vosoritide combined with standard of care or standard of care alone. The primary and secondary aims of the study are to evaluate the safety and efficacy of vosoritide in children with cervicomedullary compression at risk of requiring decompression surgery. The trial will be carried out in specialized skeletal dysplasia treatment centers with well established multidisciplinary care pathways and standardized approaches to the neurosurgical management of cervicomedually compression. After 2 years, infants randomized to standard of care alone will be eligible to switch to vosoritide plus standard of care for an additional 3 years. This pioneering trial hopes to address the important question as to whether treatment with vosoritide at an early age in infants at risk of requiring cervicomedullary decompression surgery is safe, and can improve growth at the foramen magnum and spinal canal alleviating stenosis. This in turn may reduce compression of surrounding structures including the neuraxis and spinal cord, which could alleviate future morbidity and mortality.Trial registrations: ClinicalTrials.gov, NCT04554940; EudraCT number, 2020-001055-40.

Cerebrospinal fluid liquid biopsy for detecting somatic mosaicism in brain.

Brain somatic mutations are an increasingly recognized cause of epilepsy, brain malformations and autism spectrum disorders and may be a hidden cause of other neurodevelopmental and neurodegenerative disorders. At present, brain mosaicism can be detected only in the rare situations of autopsy or brain biopsy. Liquid biopsy using cell-free DNA derived from cerebrospinal fluid has detected somatic mutations in malignant brain tumours. Here, we asked if cerebrospinal fluid liquid biopsy can be used to detect somatic mosaicism in non-malignant brain diseases. First, we reliably quantified cerebrospinal fluid cell-free DNA in 28 patients with focal epilepsy and 28 controls using droplet digital PCR. Then, in three patients we identified somatic mutations in cerebrospinal fluid: in one patient with subcortical band heterotopia the LIS1 p. Lys64* variant at 9.4% frequency; in a second patient with focal cortical dysplasia the TSC1 p. Phe581His*6 variant at 7.8% frequency; and in a third patient with ganglioglioma the BRAF p. Val600Glu variant at 3.2% frequency. To determine if cerebrospinal fluid cell-free DNA was brain-derived, whole-genome bisulphite sequencing was performed and brain-specific DNA methylation patterns were found to be significantly enriched (P = 0.03). Our proof of principle study shows that cerebrospinal fluid liquid biopsy is valuable in investigating mosaic neurological disorders where brain tissue is unavailable.

Resection of tuber centers only for seizure control in tuberous sclerosis complex.

Our previous studies suggest the tuber center is the seizure focus in tuberous sclerosis complex (TSC). We report findings from 5 epilepsy surgeries in 4 children with TSC and focal motor seizures from single tubers in primary sensorimotor cortex in which resection was limited to the cortex in the tuber center. Intraoperative electrocorticography showed epileptiform activity in the tuber center, with or without propagation to the tuber rim and surrounding perituberal cortex. Histopathology showed an abundance of dysmorphic neurons in the tuber center compared to the rim in four paired specimens, dysmorphic neurons being the reported epileptogenic cell line in TSC. Associated focal motor seizures were eliminated in all children (mean follow up 6.3 years) without postoperative deficits. Tuber center resections are a potential alternative to complete tuberectomy in patients with epileptogenic tubers in eloquent cortex and potentially also in children with a high tuber load and multifocal seizures.

Clinical seizure manifestations in the absence of synaptic connections.

We report a child with a history of temporal-parietal-occipital disconnection for epilepsy secondary to posterior quadrantic dysplasia who developed recurrent and prolonged bouts of distress and autonomic disturbance associated with EEG and PET evidence of status epilepticus confined to his disconnected cortex. These bouts were refractory to antiseizure medications but resolved following resection of the disconnected cortex. In the absence of synaptic connections, we hypothesise that his seizure-related symptoms were mediated either by neurochemical transmission in preserved vascular and lymphatic channels or by ephaptic transmission to trigeminal nerve fibres in overlying dura, producing symptoms akin to migraine. The case highlights potential means by which seizures may manifest clinically, without synaptic connections, and adds to the differential for symptoms post-disconnection surgery.

Progress in neurosurgery: Contributions of women neurosurgeons in Asia and Australasia.

At the end of the first 100 years of neurosurgery as a specialty, it is appropriate to look back and then imagine the future. As neurosurgery celebrates its first century, the increasing role of women neurosurgeons is a major theme. This article documents the early women pioneers in neurosurgery in Asia and Australasia. The contributions of these trailblazers to the origins, academics, and professional organizations of neurosurgery are highlighted. The first woman neurosurgeon of the region, Dr. T.S. Kanaka of India, completed her training in 1968, not long after the trailblazers in Europe and North America. She heralded the vibrant communities of neurosurgical women that have developed in the vast and diverse nations of the region, and the many formal and informal groups of women in neurosurgery that have introduced and promoted talented women in the profession. Contributions of women neurosurgeons to academic medicine and society as a whole are briefly highlighted, as are their challenges in this male-dominated specialty. The region is home to many deeply conservative societies; in fact, some nations in the region have not yet trained their first woman neurosurgeon. The fortitude of these individuals to achieve at the highest levels of neurosurgery indicates great potential for future growth of women in the profession, but also demonstrates the need for initiatives and advocacy to reach the full potential of gender equity.

Gradient of brain mosaic RHEB variants causes a continuum of cortical dysplasia.

Focal cortical dysplasia (FCD) and hemimegalencephaly (HME) are related malformations with shared etiologies. We report three patients with a spectrum of cortical malformations associated with pathogenic brain-specific somatic Ras homolog enriched in brain (RHEB) variants. The somatic variant load directly correlated with the size of the malformation, with upregulated mTOR activity confirmed in dysplastic tissues. Laser capture microdissection showed enrichment of RHEB variants in dysmorphic neurons and balloon cells. Our findings support the role of RHEB in a spectrum of cortical malformations confirming that FCD and HME represent a disease continuum, with the extent of dysplastic brain directly correlated with the somatic variant load.

Pediatric neurosurgery in Asia and Australasia: training and clinical practice.

OBJECTIVE: There are limited data on the pediatric neurosurgical workforce in Asia and Australasia. The training and clinical practice of pediatric neurosurgeons need to be characterized in order to identify gaps in knowledge and skills, thereby establishing a framework from which to elevate pediatric neurosurgical care in the region. METHODS: An online survey for pediatric neurosurgeons was created in REDCap (Research Electronic Database Capture), collecting demographic information and data on pediatric neurosurgical training and clinical practice. The link to answer the survey was sent to the mailing lists of the Asian Australasian Society for Pediatric Neurosurgery and the Japanese Society for Pediatric Neurosurgery, disseminated during the 2019 Asian Australasian Pediatric Neurosurgery Congress, and spread through social media. The survey was open to neurosurgeons who operated on patients ≤ 18 years old in Asian Australasian countries, whether or not they had completed fellowship training in pediatric neurosurgery. Descriptive statistics were computed and tabulated. Data were stratified and compared based on surgeon training and World Bank income group. RESULTS: A total of 155 valid survey responses were analyzed, representing neurosurgeons from 21 countries. A total of 107 (69%) considered themselves pediatric neurosurgeons, of whom 66 (43%) had completed pediatric neurosurgery training. Neurosurgeons in East Asia commonly undergo a fellowship in their home countries, whereas the rest train mostly in North America, Europe, and Australia. A majority (89%) had operating privileges, and subspecialty pediatric training usually lasted from 6 months to 2 years. On average, trained pediatric neurosurgeons perform a higher number of pediatric neurosurgical operations per year compared with nonpediatric-trained respondents (131 ± 129 vs 56 ± 64 [mean ± SD], p = 0.0001). The mean number of total neurosurgical operations per year is similar for both groups (184 ± 129 vs 178 ± 142 [mean ± SD], p = 0.80). Respondents expressed the desire to train further in pediatric epilepsy, spasticity, vascular malformations, craniofacial disorders, and brain tumors. CONCLUSIONS: Both pediatric and general neurosurgeons provide neurosurgical care to children in Asia and Australasia. There is a need to increase pediatric neurosurgery fellowship programs in the region. Skill sets and training needs in pediatric neurosurgery vary depending on the country's economic status and between pediatric-trained and nonpediatric-trained surgeons.

Genetic characterization identifies bottom-of-sulcus dysplasia as an mTORopathy.

OBJECTIVE: To determine the genetic basis of bottom-of-sulcus dysplasia (BOSD), which is a highly focal and epileptogenic cortical malformation in which the imaging, electrophysiologic, and pathologic abnormalities are maximal at the bottom of sulcus, tapering to a normal gyral crown. METHODS: Targeted panel deep sequencing (>500×) was performed on paired blood and brain-derived genomic DNA from 20 operated patients with drug-resistant focal epilepsy and BOSD. Histopathology was assessed using immunohistochemistry. RESULTS: Brain-specific pathogenic somatic variants were found in 6 patients and heterozygous pathogenic germline variants were found in 2. Somatic variants were identified in MTOR and germline variants were identified in DEPDC5 and NPRL3. Two patients with somatic MTOR variants showed a mutation gradient, with higher mutation load at the bottom of sulcus compared to the gyral crown. Immunohistochemistry revealed an abundance of dysmorphic neurons and balloon cells in the bottom of sulcus but not in the gyral crown or adjacent gyri. CONCLUSIONS: BOSD is associated with mTOR pathway dysregulation and shares common genetic etiologies and pathogenic mechanisms with other forms of focal and hemispheric cortical dysplasia, suggesting these disorders are on a genetic continuum.

Optic Radiation Tractography in Pediatric Brain Surgery Applications: A Reliability and Agreement Assessment of the Tractography Method.

BACKGROUND: Optic radiation (OR) tractography may help predict and reduce post-neurosurgical visual field deficits. OR tractography methods currently lack pediatric and surgical focus. PURPOSE: We propose a clinically feasible OR tractography strategy in a pediatric neurosurgery setting and examine its intra-rater and inter-rater reliability/agreements. METHODS: Preoperative and intraoperative MRI data were obtained from six epilepsy and two brain tumor patients on 3 Tesla MRI scanners. Four raters with different clinical experience followed the proposed strategy to perform probabilistic OR tractography with manually drawing anatomical landmarks to reconstruct the OR pathway, based on fiber orientation distributions estimated from high angular resolution diffusion imaging data. Intra- and inter-rater reliabilities/agreements of tractography results were assessed using intraclass correlation coefficient (ICC) and dice similarity coefficient (DSC) across various tractography and OR morphological metrics, including the lateral geniculate body positions, tract volumes, and Meyer's loop position from temporal anatomical landmarks. RESULTS: Good to excellent intra- and inter-rater reproducibility was demonstrated for the majority of OR reconstructions (ICC = 0.70-0.99; DSC = 0.84-0.89). ICC was higher for non-lesional (0.82-0.99) than lesional OR (0.70-0.99). The non-lesional OR's mean volume was 22.66 cm3; the mean Meyer's loop position was 29.4 mm from the temporal pole, 5.89 mm behind of and 10.26 mm in front of the temporal ventricular horn. The greatest variations (± 1.00-3.00 mm) were observed near pathology, at the tract edges or at cortical endpoints. The OR tractography were used to assist surgical planning and guide lesion resection in all cases, no patient had new visual field deficits postoperatively. CONCLUSION: The proposed tractography strategy generates reliable and reproducible OR tractography images that can be reliably implemented in the routine, non-emergency pediatric neurosurgical setting.

Second-hit DEPDC5 mutation is limited to dysmorphic neurons in cortical dysplasia type IIA.

Focal cortical dysplasia (FCD) causes drug-resistant epilepsy and is associated with pathogenic variants in mTOR pathway genes. How germline variants cause these focal lesions is unclear, however a germline + somatic "2-hit" model is hypothesized. In a boy with drug-resistant epilepsy, FCD, and a germline DEPDC5 pathogenic variant, we show that a second-hit DEPDC5 variant is limited to dysmorphic neurons, and the somatic mutation load correlates with both dysmorphic neuron density and the epileptogenic zone. These findings provide new insights into the molecular and cellular correlates of FCD determining drug-resistant epilepsy and refine conceptualization of the epileptogenic zone.

Somatic GNAQ mutation in the forme fruste of Sturge-Weber syndrome.

OBJECTIVE: To determine whether the GNAQ R183Q mutation is present in the forme fruste cases of Sturge-Weber syndrome (SWS) to establish a definitive molecular diagnosis. METHODS: We used sensitive droplet digital PCR (ddPCR) to detect and quantify the GNAQ mutation in tissues from epilepsy surgery in 4 patients with leptomeningeal angiomatosis; none had ocular or cutaneous manifestations. RESULTS: Low levels of the GNAQ mutation were detected in the brain tissue of all 4 cases-ranging from 0.42% to 7.1% frequency-but not in blood-derived DNA. Molecular evaluation confirmed the diagnosis in 1 case in which the radiologic and pathologic data were equivocal. CONCLUSIONS: We detected the mutation at low levels, consistent with mosaicism in the brain or skin (1.0%-18.1%) of classic cases. Our data confirm that the forme fruste is part of the spectrum of SWS, with the same molecular mechanism as the classic disease and that ddPCR is helpful where conventional diagnosis is uncertain.

Potential delays in referral and assessment for epilepsy surgery in children with drug-resistant, early-onset epilepsy.

OBJECTIVE: To study potential delays in epilepsy surgery in children with drug-resistant epilepsy (DRE) of early-onset. METHODS: Medical records were reviewed from 87 children with DRE and seizure onset before age 3 years who underwent epilepsy surgery between 2006 and 2015. Information was obtained about each child's epilepsy, treatment and specific time points in management. Time intervals along diagnostic, investigative, treatment and referral pathways were calculated. RESULTS: Median ages at seizure onset, when seen in the epilepsy surgery program and surgery were 5.9 (IQR 10), 19 (IQR 29) and 36 (IQR 67) months; the median delay from seizure onset to surgery was 30 (IQR 67) months. Most children were promptly diagnosed, treated, investigated and seen by a pediatric neurologist. Focal abnormalities were reported on initial EEGs and MRIs in most children, and DRE developed within a median of 6.3 months from commencement of medication. There were median durations of 6.2 months between seeing a neurologist and being seen in the epilepsy surgery program, and then 6.1 months in determining surgical candidacy. Median durations from potential indications for a surgical evaluation to agreed surgical candidacy were 10 (DRE), 12 (focal MRI) and 17 (focal EEG) months. Children received a median of six antiepileptic drugs prior to surgery. Median interval from agreed surgical candidacy to surgery was only 3 months. There were longer durations from seizure onset to surgery in children needing PET (p = 0.001) and in children with seizure-free periods (p < 0.001), and shorter durations in children with a history of infantile spasms (p = 0.01). SIGNIFICANCE: Delays in referral of children for epilepsy surgery are reported. Delays in assessment may be specific to centralized children's hospitals in public health systems.

A systematic evaluation of intraoperative white matter tract shift in pediatric epilepsy surgery using high-field MRI and probabilistic high angular resolution diffusion imaging tractography.

OBJECTIVE Characterization of intraoperative white matter tract (WMT) shift has the potential to compensate for neuronavigation inaccuracies using preoperative brain imaging. This study aimed to quantify and characterize intraoperative WMT shift from the global hemispheric to the regional tract-based scale and to investigate the impact of intraoperative factors (IOFs). METHODS High angular resolution diffusion imaging (HARDI) diffusion-weighted data were acquired over 5 consecutive perioperative time points (MR1 to MR5) in 16 epilepsy patients (8 male; mean age 9.8 years, range 3.8-15.8 years) using diagnostic and intraoperative 3-T MRI scanners. MR1 was the preoperative planning scan. MR2 was the first intraoperative scan acquired with the patient's head fixed in the surgical position. MR3 was the second intraoperative scan acquired following craniotomy and durotomy, prior to lesion resection. MR4 was the last intraoperative scan acquired following lesion resection, prior to wound closure. MR5 was a postoperative scan acquired at the 3-month follow-up visit. Ten association WMT/WMT segments and 1 projection WMT were generated via a probabilistic tractography algorithm from each MRI scan. Image registration was performed through pairwise MRI alignments using the skull segmentation. The MR1 and MR2 pairing represented the first surgical stage. The MR2 and MR3 pairing represented the second surgical stage. The MR3 and MR4 (or MR5) pairing represented the third surgical stage. The WMT shift was quantified by measuring displacements between a pair of WMT centerlines. Linear mixed-effects regression analyses were carried out for 6 IOFs: head rotation, craniotomy size, durotomy size, resected lesion volume, presence of brain edema, and CSF loss via ventricular penetration. RESULTS The average WMT shift in the operative hemisphere was 2.37 mm (range 1.92-3.03 mm) during the first surgical stage, 2.19 mm (range 1.90-3.65 mm) during the second surgical stage, and 2.92 mm (range 2.19-4.32 mm) during the third surgical stage. Greater WMT shift occurred in the operative than the nonoperative hemisphere, in the WMTs adjacent to the surgical lesion rather than those remote to it, and in the superficial rather than the deep segment of the pyramidal tract. Durotomy size and resection size were significant, independent IOFs affecting WMT shift. The presence of brain edema was a marginally significant IOF. Craniotomy size, degree of head rotation, and ventricular penetration were not significant IOFs affecting WMT shift. CONCLUSIONS WMT shift occurs noticeably in tracts adjacent to the surgical lesions, and those motor tracts superficially placed in the operative hemisphere. Intraoperative probabilistic HARDI tractography following craniotomy, durotomy, and lesion resection may compensate for intraoperative WMT shift and improve neuronavigation accuracy.

Centre of epileptogenic tubers generate and propagate seizures in tuberous sclerosis.

SEE DUCHOWNY DOI101093/AWW216 FOR A SCIENTIFIC COMMENTARY ON THIS ARTICLE: Multiple seizure foci, seizure propagation and epileptic spasms complicate presurgical seizure localization in tuberous sclerosis. Furthermore, controversy exists about the contribution of tubers, perituberal cortex and the underlying genetic abnormality to epileptogenesis. We aimed to determine the epileptogenic substrate in tuberous sclerosis by studying spatio-temporal patterns of seizure onset and propagation on intracranial EEG recordings in which multiple depth and surface electrodes sampled multiple tubers and perituberal cortex. Ten intracranial EEG recordings (seven extraoperative, three intraoperative) from 10 children with tuberous sclerosis were analysed. Notable thickening and signal abnormality in the centre of many tubers on magnetic resonance imaging led to tuber centres being recorded with depth electrodes. Spatially-meaningful bipolar montages were reformatted incorporating channels recording only from the tuber centre, tuber rim and perituberal cortex. Interictal epileptiform discharges and ictal rhythms were analysed visually for location, field, morphology, frequency, latency and temporal dispersion. Fifteen electroclinically distinct seizures were recorded in the 10 patients. Seizure onset was recorded in tubers in all 15 electroclinically distinct seizures; in 9/10 electroclinically distinct seizures recorded with optimal spatial sampling, seizure onset was recorded in the tuber centre, with or without involvement of the tuber rim but not perituberal cortex. Quantitative electroencephalography analysis by pairwise cross-correlation confirmed that the tuber centre led the tuber rim and perituberal cortex during interictal, preictal and ictal spike trains. Seizure propagation was observed in 10/15 electroclinically distinct seizures, being tuber-to-tuber in all. Seven of the 17 tubers showing seizure propagation activated an independent ictal rhythm, morphologically distinct from that seen in seizure onset region (intra-ictal activation). Of the total 48 tubers sampled, 16 exhibited seizure onset, 17 were involved in seizure propagation and 40 exhibited interictal epileptiform discharges, 33 independent and seven propagated. Seizure onsets were recorded in 16/33 tubers with independent interictal epileptiform discharges, but 0/7 tubers with only propagated epileptiform discharges or 0/8 tubers with no epileptiform discharges (P = 0.003). Seizure onsets were recorded from 4/7 tubers with and 0/10 tubers without intra-ictal activation (P = 0.015). Thus, focal seizures and interictal epileptiform discharges in tuberous sclerosis arise in the centre of epileptogenic tubers and propagate to the tuber rim, perituberal cortex and other epileptogenic tubers. Rhythmic interictal epileptiform discharges and intra-ictal activation of propagated ictal rhythms are potential biomarkers of epileptogenic tubers. Interictal and ictal EEG features of epileptogenic tubers have similarities to focal cortical dysplasia type II, consistent with the reported imaging, histological and molecular similarities.