Extraoperative electrical stimulation mapping in epilepsy presurgical evaluation: a proposal and review of the literature.

BACKGROUND: Electrical stimulation mapping (ESM) is an important tool for the localization of the seizure onset zone (SOZ) in patients with medically resistant epilepsy (MRE). ESM is the gold standard for the identification of eloquent cortex in epilepsy surgery candidates. However, there is no standard protocol outlining how to perform ESM, to obtain the most useful information possible. The objective of this study, after reviewing the literature concerning ESM, is to propose a unifying technique to validate reliable data across different centers. METHODS: In this manuscript we summarize this technique from its origin to present, and review protocols used in other centers. We also describe a protocol that has been used in our institution, which utilizes depth electrodes. RESULTS: The most common type of ESM uses a "close-loop" system, bipolar and high frequency stimulation (50 Hz). We propose to use a pulse width of 300 µs, current spanning 1-6 mA in depth electrodes and 1-11 mA in subdural-grids. Stimulation time of 5 s maximum and at least 10 s break in between the stimulations. CONCLUSIONS: ESM is a useful tool for understanding eloquent cortex as well as the epilepsy network, although there is no clear consensus regarding how it should be performed.

Epilepsy surgery in stroke-related epilepsy.

PURPOSE: To provide a descriptive analysis on the presurgical evaluation and surgical management of a cohort of patients with stroke related epilepsy (SRE). METHODS: We retrospectively examined the clinical characteristics, results of non-invasive and invasive presurgical evaluation, surgical management and outcome of consecutive patients with drug-resistant SRE in our institution from January 1, 2013 to January 1, 2020. RESULTS: Twenty-one of 420 patients (5%) who underwent intracranial EEG (iEEG), resective epilepsy surgery and/or vagus nerve stimulation (VNS) placement, had SRE. Of 13 patients who had iEEG, the ictal onset (IO) was exclusively within the stroke lesion in only one patient. In five patients the IO was extra-lesional and in the remaining seven patients it included the stroke lesion as well as extra-lesional structures. The IO included the mesial temporal region in 11 of the 13 patients (85%). The posterior margin of the stroke lesion was always involved. Five patients underwent surgery without iEEG. In total, 10 patients underwent resective surgery, four VNS placement and two had both corpus callosotomy and VNS placement. Of the patients who had resective surgery, nine were Engel I or II at last follow up. CONCLUSION: We found that seizures in patients with drug resistant SRE were more frequently originated in the mesial temporal region than in the stroke lesion itself. Despite the complex epileptic network underlying drug-resistant SRE, a thorough presurgical assessment and adequate use of surgical options can lead to excellent surgical outcomes.

Concordance between fMRI and Wada test for memory lateralization in temporal lobe epilepsy: A meta-analysis and systematic review.

OBJECTIVE: The Wada test (WT) is increasingly being replaced by functional magnetic resonance imaging (fMRI) to evaluate memory lateralization before temporal lobe epilepsy (TLE) surgery. We aimed to determine, via meta-analysis, agreement between the two tests and identify predictors of disagreement. METHODS: We performed a systematic search for studies comparing WT and fMRI for memory lateralization with individual-patient data. If results were provided as laterality indexes instead of hemispheric lateralization, the cutoff point for memory lateralization was set to the usual ±2 for WT and ±0.20 for fMRI. We also evaluated results at our Epilepsy Center. RESULTS: Seven published series plus our own were included, comprising 124 patients. Wada test was performed by recognizing objects in half of the studies, and scenes, drawings, and words in the rest. All used scenes or pictures encoding for fMRI. Wada test-fMRI agreement across the studies ranged from 21.1 to 100%, averaging 46.8% (95% confidence interval [CI]: 37.6-56.0%). When cases with bilateral memory in either test were excluded, agreement reached 78.7% (95% CI: 67.6-89.8%), and concordance with contralateral TLE foci 86.4% for the WT and 83.0% for fMRI. Higher agreement was associated with using multiple items during WT (p = 0.001) and higher disagreement with presence of a lesion on MRI (p = 0.024). Binary logistic regression confirmed use of multiple items on WT as the strongest predictor of agreement (odds ratio [OR]: 6.95, 95% CI: 1.84-26.22; p = 0.004) and a bilateral result on the WT or fMRI of disagreement (OR: 0.24, 95% CI: 0.07-0.89 and OR: 0.12, 95% CI: 0.03-0.45; p < 0.05). CONCLUSION: Concordance between WT and fMRI for memory lateralization is low in patients with TLE and bilateral memoryl memory distribution or a structural etiology, and it improves with encoding of a varied set of items. Both tests can help to lateralize the TLE foci.

Memory loss and memory reorganization patterns in temporal lobe epilepsy patients undergoing anterior temporal lobe resection, as demonstrated by pre-versus post-operative functional MRI.

This study was aimed to longitudinally assess memory function and whole-brain memory circuit reorganization in patients with temporal lobe epilepsy (TLE) by comparing activation potentials before versus after anterior temporal lobe (ATL) resection. Nineteen patients with medically-intractable TLE (10 left TLE, 9 right TLE) and 15 healthy controls were enrolled. Group analyses were conducted pre- and post-ATL of a novelty complex scene-encoding paradigm comparing areas of blood oxygen-level-dependent (BOLD) signal activations on functional magnetic resonance imaging (fMRI). None of the pre-operative patient characteristics we studied predicted the extent of pre- to post-operative memory loss. On fMRI, extra-temporal activations were detected pre-operatively in both LTLE and RTLE, particularly in the frontal lobe. Greater activations also were noted in the contralateral hippocampus and parahippocampus in both groups. Performing within-subject comparisons, post-op relative to pre-op, pronounced ipsilateral activations were identified in the left parahippocampal gyrus in LTLE, versus the right middle temporal gyrus in RTLE patients. Memory function was impaired pre-operatively but declined after ATL resection in both RTLE and LTLE patients. Post-operative fMRI results indicate possible functional adaptations to ATL loss, primarily occurring within the left parahippocampal gyrus versus right middle temporal gyrus in LTLE versus RTLE patients, respectively.

Subjective memory evaluation before and after temporal lobe epilepsy surgery.

Subjective memory (SM), a self-evaluation of memory, in contrast to objective memory (OM) measured by neuropsychological testing, is less well studied in patients with epilepsy. We assessed SM before and after temporal lobectomy. The Frequency of Forgetting 10 scale (FOF-10), developed to evaluate SM in dementia, was given before and one year after temporal lobectomy. Reliability and validity for use in epilepsy were first assessed. Measures of depression (CES-D) and neuroticism (PANAS) were done before and after surgery as well as complete neuropsychological assessment of OM. Correlation analysis between FOF-10 results and all the other variables was implemented. In 48 patients the FOF-10 was reliable and valid showing high internal consistency in all items (Cronbach's alpha >0.82) and high reproducibility (p<0.01). The FOF-10 also correlated with the memory assessment clinics self rating scale (MAC-S) (p<0.01). FOF-10 scores improved or were unchanged postoperatively in 28 patients (58%) and worsened in 20 (42%). The FOF-10 did not significantly correlate with memory scores from neuropsychological testing but did correlate with perceived word finding difficulty (p<0.001) and postoperative depression (p<0.05). A reduction in number of antiepileptic drugs (AEDs) after surgery distinguished those with improved postoperative SM. No correlation was found between SM and neuroticism, side of surgery or number of seizures. The FOF-10 is a brief and reliable measure of subjective memory in patients with epilepsy. Perceived memory impairment reflects more emotional state, language problems and quantity of AEDs than actual defects in memory function. These results would potentially be useful in presurgical counselling and management of memory issues after temporal lobe surgery.

Language mapping in temporal lobe epilepsy in children: special considerations.

Temporal lobe epilepsy (TLE) in children is a slightly different entity than TLE in adults not only because of its semiology and pathology but also because of the different approach to surgical treatment. Presurgical investigations for eloquent cortex, especially language, must take these differences into account. Most diagnostic tests were created for adults, and many of the assessment tools need to be adapted for children because they are not just small adults. This paper will highlight the specific challenges and solutions in mapping language in a pediatric population with TLE.

Psychosocial status after pediatric traumatic brain injury: a subtype analysis using the Child Behavior Checklist.

This study identified subtypes of psychosocial functioning in children who had sustained traumatic brain injury (TBI). Child Behavior Checklist (CBCL) profiles for 92 participants, aged 12 to 18 years, who had sustained a mild, moderate, or severe TBI were subjected to Q-Factor analysis. Sixty-four of the participants (75%) were classified into a four-category psychosocial typology labelled Normal (n = 32), Attention (n = 14), Delinquent (n = 10), and Withdrawn-Somatic (n = 8). This typology was found to overlap in part with previous TBI psychosocial typology (Butler et al., 1997), and with three of the clinical profile types derived by Achenbach (1993) for the CBCL. The majority of participants, including those who sustained severe TBI, were assigned to the Normal subtype and the overall level of psychosocial deviance was relatively mild in the other three subtypes. The results of this study support previous typology efforts and confirm the heterogeneous presentation of social and emotional functioning following TBI.