Sulcus-centered resection for focal cortical dysplasia type II: surgical techniques and outcomes

Practical measurements distinguishing physiological and pathological stereoelectroencephalography channels based on high-frequency oscillations in the human brain

OBJECTIVE

The present study aimed to identify various distinguishing features for use in the accurate classification of stereoelectroencephalography (SEEG) channels based on high-frequency oscillations (HFOs) inside and outside the epileptogenic zone (EZ).

METHODS

HFOs were detected in patients with focal epilepsy who underwent SEEG. Subsequently, HFOs within the seizure-onset and early spread zones were defined as pathological HFOs, whereas others were defined as physiological. Three features of HFOs were identified at the channel level, namely, morphological repetition, rhythmicity, and phase-amplitude coupling (PAC). A machine-learning (ML) classifier was then built to distinguish two HFO types at the channel level by application of the above-mentioned features, and the contributions were quantified. Further verification of the characteristics and classifier performance was performed in relation to various conscious states, imaging results, EZ location, and surgical outcomes.

RESULTS

Thirty-five patients were included in this study, from whom 166  104 pathological HFOs in 255 channels and 53 374 physiological HFOs in 282 channels were entered into the analysis pipeline. The results revealed that the morphological repetitions of pathological HFOs were markedly higher than those of the physiological HFOs; this was also observed for rhythmicity and PAC. The classifier exhibited high accuracy in differentiating between the two forms of HFOs, as indicated by an area under the curve (AUC) of 0.89. Both PAC and rhythmicity contributed significantly to this distinction. The subgroup analyses supported these findings.

SIGNIFICANCE

The suggested HFO features can accurately distinguish between pathological and physiological channels substantially improving its usefulness in clinical localization.

PLAIN LANGUAGE SUMMARY

In this study, we computed three quantitative features associated with HFOs in each SEEG channel and then constructed a machine learning-based classifier for the classification of pathological and physiological channels. The classifier performed well in distinguishing the two channel types under different levels of consciousness as well as in terms of imaging results, EZ location, and patient surgical outcomes.

Evaluating intraoperative ultrasound (IOUS) in focal cortical dysplasia (FCD) resection surgery: A systematic review

Background

Surgery is the best approach to treating focal cortical dysplasia (FCD)-related epilepsy; yet, it has suboptimal outcomes because distinguishing the boundaries between the FCD region and normal brain tissue intraoperatively poses a challenge. The use of intraoperative ultrasound (IOUS) helps demarcate FCD lesion borders leading to more accurate intraoperative resection. In this review, the use of IOUS for the resection of FCD was evaluated.

Methods

This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The Medline, Embase, Cochrane Library, Scopus Library, and Dynamed Library databases were searched, and two independent reviewers examined the articles. The search terms related to "drug-resistant epilepsy" and "intraoperative ultrasound." The results between January 2008 and April 2022 were abridged for FCD type, ultrasound resolution, extent of lesion resection, correction of brain shift, postoperative neurological deficits, and postoperative seizure freedom (Engel classification).

Results

Ten articles were included in the study. The parameters used to assess the efficacy of IOUS in FCD surgery were ultrasound resolution, demarcation of lesion boundaries, correction of brain shift, postoperative neurological deficits, and seizure freedom. Most studies have shown that IOUS produces high-resolution images. Surgery for Type 2 FCD patients had better outcomes than surgery for Type 1 FCD patients due to better visualization by IOUS. Patients were classified as Engel class 1 or class 2 postoperatively. Eight studies found that IOUS was superior to magnetic resonance imaging in brain shift correction.

Conclusion

The preliminary results look promising, especially for the international league against epilepsy class 2 FCD. However, there is a need for more high-quality research evaluating the use of IOUS in FCD and comparing it to other intraoperative imaging modalities.

Clinical characteristics and surgical outcomes in children with mild malformation of cortical development and oligodendroglial hyperplasia in epilepsy

OBJECTIVE

Mild malformation of cortical development with oligodendroglial hyperplasia in epilepsy (MOGHE) is a new and rare histopathological entity of cortical developmental malformations. The clinical characteristics of MOGHE remain challenging.

METHODS

Children with histologically confirmed MOGHE were retrospectively studied. The clinical findings, electroclinical and imaging features, and postoperative outcomes were analyzed, and previously published studies were reviewed up to June 2022.

RESULTS

Thirty-seven children were included in our cohort. Clinical characteristics included early onset in infancy (94.6% before 3 years), multiple seizure types, and moderate or severe delay. Epileptic spasm is the most common seizure type and initial manifestation. The lesions were mainly multilobar (59.5% multiple lobes and 8.1% hemispheres), and predominance in the frontal lobe was observed. The interictal EEG pattern was circumscribed or widespread. The prominent MRI characteristics were cortical thickening, cortical/subcortical hyperintense T2/FLAIR signal, and blurring at the GM and WM transition. Among the 21 children followed up for more than 1 year after surgery, 76.2% were seizure-free. Preoperative interictal circumscribed discharges and larger resections were significantly associated with a good postoperative outcome. The clinical features of 113 patients in the reviewed studies were similar to those we reported, but the lesions were mainly unilobar (73.5%) and Engel I was achieved in only 54.2% after surgery.

SIGNIFICANCE

Distinct clinical characteristics in MOGHE, especially age at onset, epileptic spasm, and age-related MRI characteristics, can help in early diagnosis. Preoperative interictal discharge and surgical strategy may be predictors of postoperative outcomes.

Is intracranial electroencephalography mandatory for MRI-negative neocortical epilepsy surgery?

OBJECTIVE

MRI-negative focal epilepsy is one of the most challenging cases in surgical epilepsy treatment. Many epilepsy centers recommend intracranial electroencephalography (EEG) for MRI-negative cases, especially neocortical epilepsy. This retrospective study aimed to explore whether intracranial monitoring is mandatory in MRI-negative neocortical epilepsy surgery and the factors that significantly influence the decision on whether to perform intracranial recording.

METHODS

In this study, consecutive surgical patients with focal MRI-negative neocortical epilepsy were recruited. All patients underwent routine preoperative evaluation according to the dedicated protocol of the authors' epilepsy center to determine the treatment strategy. Patients were divided into two groups according to the surgical strategy, i.e., a direct group and a stereo-EEG (SEEG)-guided group. History of epilepsy, seizure frequency, interictal and ictal EEG data, PET data, PET/MRI coregistration data, neuropathological findings, and surgical outcomes were compared between the two groups. Multivariate analysis was performed to identify factors influencing the decision to perform SEEG monitoring.

RESULTS

Sixty-four patients were included in this study, 19 and 45 of whom underwent direct and SEEG-guided cortical resection, respectively. At an average follow-up of 3.9 years postoperatively, 56 patients (87.5%) had Engel class I results without permanent neurological deficits. Surgical outcomes were not significantly different between the direct and SEEG-guided groups (94.7% vs 84.4%). PET hypometabolic abnormalities were detected in all patients. There were significant differences between the two groups in the extent of hypometabolism (focal vs nonfocal, p < 0.01) and pathological subtype (focal cortical dysplasia type II vs others, p = 0.03). Multivariate analysis revealed that the extent of hypometabolism (OR 0.01, 95% CI 0.00-0.15; p = 0.001) was the only independent factor affecting the treatment strategy.

CONCLUSIONS

Careful selection of patients with MRI-negative neocortical epilepsy may yield favorable outcomes after direct cortical resection without intracranial monitoring. PET/MRI coregistration plays an essential role in the preoperative evaluation and subsequent resection of these patients. Intracranial monitoring is not a mandatory requirement for surgery if the focal hypometabolic areas are consistent with the findings of semiology and scalp EEG.

Contralesional macrostructural plasticity in patients with frontal low-grade glioma: a voxel-based morphometry study

PURPOSE

Neuroplasticity can partially compensate for the neurological deficits caused by brain tumors. However, the structural plasticity of the brain caused by brain tumors is not fully understood. This study aimed to assess the structural plasticity of the contralesional hemisphere in patients with frontal low-grade gliomas (LGGs).

METHODS

A total of 25 patients with left frontal LGGs (LFLGGs), 19 patients with right frontal LGGs (RFLGGs), and 25 healthy controls (HCs) were enrolled in this study. High-resolution structural T1-weighted imaging and fluid attenuation inversion recovery were performed on all participants. Voxel-based morphometry (VBM) analysis was used to detect differences in the brain structural plasticity between patients with unilateral LGGs and HCs.

RESULTS

VBM analysis revealed that compared with HCs, the gray matter volume (GMV) of the contralesional putamen and amygdala was significantly smaller and larger in the patients with RFLGGs and LFLGGs, respectively, while the GMVs of the contralesional cuneus and superior temporal gyrus (STG) were significantly larger in the patients with LFLGGs. The surviving clusters of the right hemisphere included 1357 voxels in the amygdala, 1680 voxels in the cuneus, 384 voxels in the STG, and 410 voxels in the putamen. The surviving clusters of the left hemisphere were 522 voxels in the amygdala and 320 voxels in the putamen.

CONCLUSION

The unilateral frontal LGGs are accompanied by structural plasticity in the contralesional cortex and vary with tumor laterality. Contralesional structural reorganization may be one of the physiological basis for functional reorganization or compensation in the frontal LGGs.

Intrinsic and secondary epileptogenicity in focal cortical dysplasia type II

OBJECTIVE

Favorable seizure outcome is reported following resection of bottom-of-sulcus dysplasia (BOSD). We assessed the distribution of epileptogenicity and dysplasia in and around BOSD to better understand this clinical outcome and the optimal surgical approach.

METHODS

We studied 27 children and adolescents with magnetic resonance imaging (MRI)-positive BOSD who underwent epilepsy surgery; 85% became seizure-free postresection (median = 5.0 years follow-up). All patients had resection of the dysplastic sulcus, and 11 had additional resection of the gyral crown (GC) or adjacent gyri (AG). Markers of epileptogenicity were relative cortical hypometabolism on preoperative 18 F-fluorodeoxyglucose (FDG) positron emission tomography (PET), and spiking, ripples, fast ripples, spike-high-frequency oscillation cross-rate, and phase amplitude coupling (PAC) on preresection and postresection electrocorticography (ECoG), all analyzed at the bottom-of-sulcus (BOS), top-of-sulcus (TOS), GC, and AG. Markers of dysplasia were increased cortical thickness on preoperative MRI, and dysmorphic neuron density and variant allele frequency of somatic MTOR mutations in resected tissue, analyzed at similar locations.

RESULTS

Relative cortical metabolism was significantly reduced and ECoG markers were significantly increased at the BOS compared to other regions. Apart from spiking and PAC, which were greater at the TOS compared to the GC, there were no significant differences in PET and other ECoG markers between the TOS, GC, and AG, suggesting a cutoff of epileptogenicity at the TOS rather than a tapering gradient on the cortical surface. MRI and tissue markers of dysplasia were all maximal in the BOS, reduced in the TOS, and mostly absent in the GC. Spiking and PAC reduced significantly over the GC after resection of the dysplastic sulcus.

SIGNIFICANCE

These findings support the concept that dysplasia and intrinsic epileptogenicity are mostly limited to the dysplastic sulcus in BOSD and support resection or ablation confined to the MRI-visible lesion as a first-line surgical approach. 18 F-FDG PET and ECoG abnormalities in surrounding cortex seem to be secondary phenomena.

Brain-clinical signatures for vagus nerve stimulation response

AIM

Vagus nerve stimulation (VNS) is a valuable treatment for drug-resistant epilepsy (DRE) without the indication of surgical resection. The clinical heterogeneity of DRE has limited the optimal indication of choice and diagnosis prediction. The study aimed to explore the correlations of brain-clinical signatures with the clinical phenotype and VNS responsiveness.

METHODS

A total of 89 DRE patients, including VNS- (n = 44) and drug-treated (n = 45) patients, were retrospectively recruited. The brain-clinical signature consisted of demographic information and brain structural deformations, which were measured using deformation-based morphometry and presented as Jacobian determinant maps. The efficacy and presurgical differences between these two cohorts were compared. Then, the potential of predicting VNS response using brain-clinical signature was investigated according to the different prognosis evaluation approaches.

RESULTS

The seizure reduction was higher in the VNS-treated group (42.50%) as compared to the drug-treated group (12.09%) (p = 0.11). Abnormal imaging representation, showing encephalomalacia (p_corrected  = 0.03), was commonly observed in the VNS-treated group (p = 0.04). In the patients treated with VNS, the mild/subtle brain abnormalities indicated higher seizure frequency (p = 0.03) and worse VNS response (p = 0.04). The partial least square regression analysis showed a moderate prediction potential of brain-clinical signature for VNS response (p < 0.01). The increase in the pre-VNS seizure frequency and structural etiology could indicate a worse prognosis (higher McHugh classification).

CONCLUSION

The brain-clinical signature illustrated its clinical potential in predicting the VNS response, which might allow clinicians to personalize treatment decisions for DRE patients.

Voxel-Based Morphometric MRI Postprocessing-Assisted Laser Interstitial Thermal Therapy for Focal Cortical Dysplasia-Suspected Lesions: Technique and Outcomes

BACKGROUND

MRI-guided laser interstitial thermal therapy (MRgLITT) is a novel treatment modality for focal cortical dysplasia (FCD). However, identifying the location and extent of subtle FCD by visual analysis during MRgLITT remains challenging.

OBJECTIVE

To introduce voxel-based morphometric MRI postprocessing into the procedure of MRgLITT for FCD-suspected lesions and assess the complementary value of the MRI postprocessing technique for the trajectory design and thermal parameter setting of MRgLITT.

METHODS

Junction and normalized fluid-attenuated inversion recovery signal intensity images were used to detect the gray-white matter junction blurring and cortical fluid-attenuated inversion recovery hyperintensity, respectively. According to the 2 postprocessing images, the region of interest (ROI) for ablation was drawn. The main principle of presurgical planning is that the trajectory of the laser fiber was designed as far as possible along the long axis of the ROI while the extent of planned ablation covered the entire ROI. The subsequent intraoperative procedure was performed under the guidance of the presurgical plan.

RESULTS

Nine patients with epilepsy with FCD-suspected lesions underwent MRgLITT with the assistance of MRI postprocessing images. Among them, 4 patients were junction positive, 2 patients were normalized fluid-attenuated inversion recovery signal intensity positive, and the remaining 3 patients were positive for both. Postsurgical MRI demonstrated that the ROIs were ablated entirely in 7 patients. Engel Ia, Ib, and IV scores were obtained at 1-year follow-up for 6, 1, and 2 patients, respectively.

CONCLUSION

MRI postprocessing provides complementary information for designing the laser fiber trajectory and subsequent ablation for FCDs.

Extended resection for seizure control of pure motor strip focal cortical dysplasia during awake craniotomy: illustrative case

BACKGROUND

Focal cortical dysplasias (FCD) represent highly intrinsically epileptogenic lesions that require complete resection for seizure control. Resection of pure motor strip FCD can be challenging. Effective control of postoperative seizures is crucial and extending the boundaries of resection in an eloquent zone remains controversial.

OBSERVATIONS

The authors report a 52-year-old right-handed male with refractory epilepsy. The seizure phenotype was a focal crisis with preserved awareness and a clonic motor onset of right-hemibody. Epilepsy surgery protocol demonstrated a left pure motor strip FCD and a full-awake resective procedure with motor brain mapping was performed. Further resection of surgical boundaries monitoring function along intraoperative motor tasks with no direct electrical stimulation corroborated by intraoperative-neuromonitorization was completed as the final part of the surgery. In the follow-up period of 3-years, the patient has an Engel-IB seizure-control with mild distal lower limb palsy and no gate compromise.

LESSONS

This report represents one of the few cases with pure motor strip FCD resection. In a scenario similar to this case, the authors consider that this variation can be useful to improve seizure control and the quality of life of these patients by extending the resection of a more extensive epileptogenic zone minimizing functional damage.

Interictal pattern on scalp electroencephalogram predicts excellent surgical outcome of epilepsy caused by focal cortical dysplasia

OBJECTIVE

Focal cortical dysplasia (FCD) represents an essential cause of drug-resistant epilepsy with surgery as an effective treatment option. This study aimed to identify the important predictors of favorable surgical outcomes and the impact of the interictal scalp electroencephalogram (EEG) patterns in predicting postsurgical seizure outcomes.

METHODS

We retrospectively evaluated 210 consecutive patients between 2015 and 2019. They were diagnosed with FCD by pathology, underwent resection, and had at least one year of postsurgical follow-up. Predictors of seizure freedom were analyzed.

RESULTS

Based on the information at the latest follow-up, seizure outcome was classified as Engel Class I (seizure-free) in 81.4% and Engel Class II-IV (non-seizure-free) in 18.6% of patients. There were 43, 105, and 62 cases of FCD type I, type II, and type III, respectively. The interictal EEG showed a repetitive discharge pattern (REDP) in 87 (41.4%) patients, polyspike discharge pattern (PDP) in 41 (19.5%), and the coexistence of REDP and PDP in the same location in 32 (15.2%) patients. The analyzed patterns in order of frequency were repetitive discharges lasting 5 seconds or more (32.4%); polyspikes (16.7%); RED type 1 (11.4%); continuous epileptiform discharges occupying >80% of the recording (11.4%); RED type 2 (6.2%); brushes (3.3%); focal, fast, continuous spikes (2.4%); focal fast rhythmic epileptiform discharges (1.43%); and frequent rhythmic bursting epileptiform activity (1.4%). The coexistence of REDP and PDP in the same location on scalp EEG and complete resection of the assumed epileptogenic zone (EZ) was independently associated with favorable postsurgical prognosis.

SIGNIFICANCE

Resective epilepsy surgery for intractable epilepsy caused by FCD has favorable outcomes. Interictal scalp EEG patterns were revealed to be predictive of excellent surgical outcomes and may help clinical decision-making and enable better presurgical evaluation.

Predictors of postoperative long-term seizure outcome in pediatric patients with focal cortical dysplasia type II at a German tertiary epilepsy center

OBJECTIVE

Focal cortical dysplasia (FCD) is a common cause of early-onset intractable epilepsy, and resection is a highly sufficient treatment option. In this study, the authors aimed to provide a retrospective analysis of pre- and postoperative factors and their impact on postoperative long-term seizure outcome.

METHODS

The postoperative seizure outcomes of 50 patients with a mean age of 8 ± 4.49 years and histologically proven FCD type II were retrospectively analyzed. Furthermore, pre- and postoperative predictors of long-term seizure freedom were assessed. The seizure outcome was evaluated based on the International League Against Epilepsy (ILAE) classification.

RESULTS

Complete resection of FCD according to MRI criteria was achieved in 74% (n = 37) of patients. ILAE class 1 at the last follow-up was achieved in 76% (n = 38) of patients. A reduction of antiepileptic drugs (AEDs) to monotherapy or complete withdrawal was achieved in 60% (n = 30) of patients. Twelve patients (24%) had a late seizure recurrence, 50% (n = 6) of which occurred after reduction of AEDs. A lower number of AEDs prior to surgery significantly predicted a favorable seizure outcome (p = 0.013, HR 7.63). Furthermore, younger age at the time of surgery, shorter duration of epilepsy prior to surgery, and complete resection were positive predictors for long-term seizure freedom.

CONCLUSIONS

The duration of epilepsy, completeness of resection, number of AEDs prior to surgery, and younger age at the time of surgery served as predictors of postoperative long-term seizure outcome, and, as such, may improve clinical practice when selecting and counseling appropriate candidates for resective epilepsy surgery. The study results also underscored that epilepsy surgery should be considered early in the disease course of pediatric patients with FCD type II.

The electroclinical features and surgical outcomes of inferior perisylvian epilepsy

OBJECTIVE

To summarize the clinical and electrophysiological observations of epilepsy originating from the inferior perisylvian cortex, and analyze the potential epileptic networks underlying the semiological manifestations.

METHODS

We retrospectively analyzed patients with refractory inferior perisylvian epilepsy (IPE) who had undergone resective surgery, and then reviewed the demographic, clinical, neuroelectrophysiological, neuroimaging, surgical, histopathological, and follow-up data of the patients from the respective medical records. The selected patients were then categorized in accordance with the results of semiological analysis. Quantitative ¹⁸F-fluorodeoxyglucose-positron emission tomography (FDG-PET) analysis was performed to investigate the underlying neural network.

RESULTS

Of the 18 IPE patients assessed in this study, ipsilateral frontotemporal epileptic discharges or its onsets were the dominant interictal or ictal scalp EEG observations. In addition, oroalimentary or manual automatism was the most frequently documented manifestation, followed by facial tonic or clonic movements. Moreover, the semiological analysis identified and classified the patients into 2 patterns, and the PET statistical analyses conducted on these 2 groups revealed differences in the neural network between them.

CONCLUSION

Inferior perisylvian epilepsy possesses semiological manifestations similar to those of mesial temporal lobe epilepsy or rolandic opercular epilepsy, hence these conditions should be carefully differentiated. Performing lesionectomy or cortectomy, sparing the mesial temporal structures, was found to be an effective and safe treatment modality for IPE.

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.