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

Abstract

Objective:To determine if one-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:38 patients with median age at surgery of 10.2 (IQR: 6.0-14.1) years were included. BOSDs involved eloquent cortex in 15 patients. 87% of patients had rhythmic spiking on pre-resection ECoG. Rhythmic spiking was present in 22/24 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. 68% of resections were limited to the dysplastic sulcus, leaving the gyral crown. Histopathology was FCDIIb 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 17/22 patients. Six (16%) patients required reoperation for postoperative seizures and residual dysplasia; reoperation was not correlated with ECoG, neuroimaging or histological abnormalities in the gyral crown. At median 6.3 (IQR: 4.8-9.9) years 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 one-stage, limited corticectomy for BOSD is safe and effective for control of seizures.

The ILAE consensus classification of focal cortical dysplasia: An update proposed by an ad hoc task force of the ILAE diagnostic methods commission

“…FCDII subtypes became much better characterized as clinical entities with well‐defined EEG signatures in FCDIIa and IIb subtypes. The specificity of interictal patterns such as focal continuous rhythmic discharges and repetitive spiking have been suggested as possible predictors of the ictal‐onset zone and of favorable postresection seizure outcome 3,18,26–29 . Previous studies have shown that intrinsic epileptogenicity might not overlap with the MRI‐observed abnormality 30,31 .…”

“…They tend to localize in the depth of frontal lobe sulci (superior frontal sulcus, inferior frontal sulcus, and central sulcus) and less frequently in the parietal or temporal lobes. Direct intralesional, intraoperative, or extraoperative depth electrode electroencephalography (EEG) recordings identify a characteristic rhythmic spiking pattern in the depth of sulcus lesion 16,18 . The complete resection of the anatomic lesion achieves seizure freedom in most patients.…”

“…The specificity of interictal patterns such as focal continuous rhythmic discharges and repetitive spiking have been suggested as possible predictors of the ictal-onset zone and of favorable postresection seizure outcome. 3,18,[26][27][28][29] Previous studies have shown that intrinsic epileptogenicity might not overlap with the MRI-observed abnormality. 30,31 Correlations between histopathological and neurophysiological studies, that is, intracerebral depth electrode recordings, also provided evidence for a contribution of dysmorphic neurons to interictal spikes, fast gamma activity, and ripples.…”

Clinical utility of intraoperative electrocorticography for epilepsy surgery: A systematic review and meta‐analysis

“…iECoG guides resection by IED activity, which can better delineate the affected region in FCD 48 . This may be because cortical dysplastic brain, particularly Type II FCD, may be a driver of peri‐ and intralesional interictal continuous spikes, and thus when resected under iECoG, could correlate with seizure freedom 14,49,50 . Although iECoG‐based FCD resection, regardless of subtype, shows improvement in seizure freedom, 51,52 FCD subtypes associated with lesional pathology (Type III) have shown the best postoperative seizure freedom 20,52,53 .…”

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

“…Specific examples of high-risk surgery illustrating our clinical learning curve with Karawun include our previously reported one-stage, language dominant, insular-opercular epilepsy surgery series, and the related bottom-of-sulcus-dysplasia (BOSD) epilepsy surgery series, representing over 10 years of our clinical experience, performed with advanced fMRI and tractography guidance [ 35 , 36 ]. We demonstrated excellent surgical and seizure outcomes in both surgical series, without the need to perform additional invasive procedures for functional brain mapping, including in an awake craniotomy setting, which is unsuited for the majority of children.…”