Yahya Aghakhani

EEG-fMRI of focal epileptic spikes: Analysis with multiple haemodynamic functions and comparison with gadolinium-enhanced MR angiograms

Combined EEG‐fMRI has recently been used to explore the BOLD responses to interictal epileptiform discharges. This study examines whether misspecification of the form of the haemodynamic response function (HRF) results in significant fMRI responses being missed in the statistical analysis. EEG‐fMRI data from 31 patients with focal epilepsy were analysed with four HRFs peaking from 3 to 9 sec after each interictal event, in addition to a standard HRF that peaked after 5.4 sec. In four patients, fMRI responses were correlated with gadolinium‐enhanced MR angiograms and with EEG data from intracranial electrodes. In an attempt to understand the absence of BOLD responses in a significant group of patients, the degree of signal loss occurring as a result of magnetic field inhomogeneities was compared with the detected fMRI responses in ten patients with temporal lobe spikes. Using multiple HRFs resulted in an increased percentage of data sets with significant fMRI activations, from 45% when using the standard HRF alone, to 62.5%. The standard HRF was good at detecting positive BOLD responses, but less appropriate for negative BOLD responses, the majority of which were more accurately modelled by an HRF that peaked later than the standard. Co‐registration of statistical maps with gadolinium‐enhanced MRIs suggested that the detected fMRI responses were not in general related to large veins. Signal loss in the temporal lobes seemed to be an important factor in 7 of 12 patients who did not show fMRI activations with any of the HRFs. Hum. Brain Mapp. 22:179–192, 2004.

Temporal and Extratemporal BOLD Responses to Temporal Lobe Interictal Spikes

Summary:  Purpose: Simultaneous EEG and functional MRI (fMRI) allows measuring metabolic changes related to interictal spikes. Our objective was to investigate blood oxygenation level–dependent (BOLD) responses to temporal lobe (TL) spikes by using EEG‐fMRI recording.

Cortical and thalamic fMRI responses in partial epilepsy with focal and bilateral synchronous spikes

OBJECTIVE To determine the blood oxygen level-dependent (BOLD) responses to epileptic discharges in the thalamus and cerebral cortex in patients with partial epilepsy. METHODS Among 64 tested patients, 40 had EEG spikes during scanning and were divided in two groups: unilateral or bilateral independent spikes (29 patients) and bilaterally synchronous spikes (11 patients). Each spike topography was analyzed separately, yielding 40 studies in the first group and 17 in the second. RESULTS Forty-five percent of focal spike studies showed significant BOLD responses. Cortical activation (positive BOLD) represented the dominant response and had a better correlation with spike location than cortical deactivation (negative BOLD). In the second group, all patients had significant BOLD responses; they were more widespread compared to the first group, and deactivated areas were as important as activated regions. A thalamic response was seen in 12.5% of studies in the first group and 55% in the second. CONCLUSIONS The thalamus is involved in partial epilepsy during interictal discharges. This involvement and also cortical deactivation are more commonly seen with bilateral spikes than focal discharges. SIGNIFICANCE These findings show evidence for a role for the thalamus and a more important role for inhibition in secondary bilateral synchrony.

Analysis of the EEG–fMRI response to prolonged bursts of interictal epileptiform activity

The use of combined EEG-fMRI to study interictal epileptiform activity is increasing and has great potential as a clinical tool, but the haemodynamic response to epileptiform activity remains incompletely characterised. To this end, 19 data sets from 14 patients with prolonged bursts of focal or generalised interictal epileptiform activity lasting up to 15 s were analysed. To determine whether the inclusion of the durations of the epileptic events in the general linear model resulted in increased statistical significance of activated regions, statistical maps were generated with and without the event durations. The mean differences when including the durations were a 14.5% increase in peak t value and a 29.5% increase in volume of activation. This suggests that when analysing EEG-fMRI data from patients with prolonged bursts of interictal epileptiform activity, it is better to include the event durations. To determine whether the amplitudes and latencies of the measured responses were consistent with the general linear model, the haemodynamic response functions for bursts of different durations were calculated and compared with the model predictions. The measured amplitude of the response to the shortest duration events was consistently larger than predicted, which is consistent with studies in normal subjects. For the two data sets with the widest range of event durations, the measured amplitudes increased with the durations of the events without evidence of the plateau that was expected from the general linear model. There were no consistent differences between the measured and modelled latencies.

Patients with temporoparietal ictal symptoms and inferomesial EEG do not benefit from anterior temporal resection.

Summary:  Purpose: The role of posterior structural lesions leading to inadequate results after inferomesial temporal resection is well recognized. Here we present poor surgical outcome in six patients with nonlesional intractable epilepsy, well‐defined focal anterior and inferomesial temporal epileptic discharges, and posterior temporoparietal symptoms.

Intractable temporal lobe epilepsy with rare spikes is less severe than with frequent spikes

Objective: To analyze clinical, electrophysiologic, and neuroradiologic characteristics of a group of patients with nonlesional intractable temporal lobe epilepsy (TLE) and rare or absent interictal epileptiform abnormalities (IEA). Methods: Between 1990 and 2000, 31 patients (11 men; mean ± SD age 34.3 ± 11.7 years) with nonlesional intractable TLE were consecutively selected on the basis of the absence or paucity of IEA (<1/h) on serial scalp EEG recording; these were defined as “oligospikers.” The clinical and laboratory characteristics of oligospikers were compared with those of a group of 27 age-matched control subjects (10 men; mean ± SD age 38.5 ± 11 years), randomly selected from a pool of patients with nonlesional TLE with frequent IEA. Results: Oligospikers showed a later age at seizure onset (mean ± SD 19.1 ± 14.4 versus 10.2 ± 7.4 years; p = 0.004), lower monthly frequency of complex partial seizures (median 6 versus 12; p = 0.035), lower incidence of secondarily generalized tonic-clonic seizures (10 versus 81%; p < 0.001), and no status epilepticus (0 versus 22%) than control subjects. Also, hippocampal atrophy (HA) was less commonly found in oligospikers (55 versus 96%; p = 0.001). However, there were no differences between the two groups in the frequency of family history of epilepsy, risk factors, febrile convulsions, and type of medication. Twenty-three (74%) oligospikers and 25 (93%) control patients underwent either a selective amygdalohippocampectomy or corticoamygdalohippocampectomy. Excellent surgical outcome (Engel’s Class Ia) was found in 14 of 23 (61%) oligospikers and 17 of 25 (67%) control patients. Conclusions: This study identified a subgroup of patients with nonlesional intractable TLE with no or few IEA. Oligospikers have a later age at seizure onset, less frequent and less severe seizures, besides a lower incidence of HA. The similarity of etiologic factors compared with patients with frequent IEA suggests that the rarity of spikes could reflect a disease not really distinct but less severe, even though still intractable and incapacitating enough to consider surgery. In spite of the absence or paucity of IEA, oligospikers have excellent surgical outcome.

Surgical treatment of independent bitemporal lobe epilepsy defined by invasive recordings

Objectives: Bitemporal lobe epilepsy is commonly encountered in the evaluation of pharmacoresistant epilepsy. Yet the role of surgery in the management of these patients is unclear. This study evaluates the impact of surgery on seizure tendency and quality of life, as well as prognostic indicators in individuals with proven ictal onset bitemporal lobe epilepsy. Methods: The study population comprised all patients who underwent temporal lobe surgery over a 10 year period and had ictal onset bitemporal lobe epilepsy identified with intracranial electrode monitoring. Patients with extratemporal seizure generators were excluded. Subjects were divided into a favourable or less favourable group based on the results of surgery on seizure tendency. Results: 11 subjects were studied with a mean 5.9 years of post-surgical follow-up. Six subjects constituted the favourable outcome group. Four had a less favourable outcome and continued to have frequent seizures after surgery; however, three with less favourable seizure reduction subjectively reported improvement in quality of life after surgery as a result of reduced seizure frequency and severity, and reduced medications. No single preoperative factor was significantly different between the groups, including ictal EEG laterality, epilepsy duration, age at surgery, age at seizure onset and mesial temporal atrophy. Conclusions: Surgical resection is an important treatment option for medically intractable bitemporal epilepsy. The proportion of seizures arising from one temporal lobe is not reliable as a single indicator to prognosticate the results of surgery on seizure tendency. In addition, individuals who achieved only palliation by reducing seizure frequency experienced improvement in quality of life.

The predictive localizing value of tonic limb posturing in supplementary sensorimotor seizures

Objective: To determine whether early tonic limb posturing is reliable in lateralizing or localizing of the seizure generator in 14 patients with pharmacoresistent supplementary sensorimotor area (SSMA) seizures. Methods: All patients underwent high-quality MRI scans and stereo-EEG recordings. Results: The SSMA seizure semiology predicted focal or regional ictal onset in the SSMA in six (43%) patients: Three had a focal SSMA seizure onset, and three had a regional seizure onset with involvement of one SSMA plus adjacent neocortex. The eight remaining patients had diffuse uni- or bilateral seizure onset. Eight of 14 patients underwent a frontal or central cortical resection, but a good outcome was seen in only 3: 2 with no SSMA resection and 1 with an extensive central removal. Conclusions: SSMA semiology is suggestive of early involvement of this region but is by no means a reliable indicator that the primary SSMA contains the seizure focus.

α‐[11C]methyl‐L‐tryptophan uptake in patients with periventricular nodular heterotopia and epilepsy

Background:α‐[11C]methyl‐L‐tryptophan (α‐MTrp) positron emission tomography (PET) is a promising tool in the localization of the epileptogenic area in selected group of focal epilepsy patients. Electrophysiological evidence suggests the involvement of the neocortex in periventricular nodular heterotopia (PVNH).