Visual and Quantitative Ictal EEG Predictors of Outcome After Temporal Lobectomy

Abstract

Summary: Purpose; We investigated whether visual and quantitative ictal EEG analysis could predict surgical outcome after anteromesial temporal lobectomy (AMTL) in which mesial structures, basal, and temporal tip cortex were resected.Methods: We retrospectively reviewed 282 presurgical scalprecorded ictal EEGs (21-to 27-channel) from 75 patients who underwent AMTL. We examined the pattern of seizure onset (frequency, distribution, and evolution) and estimated the principal underlying cerebral generators by using a multiple fixed dipole model that decomposes temporal lobe activity into four sublobar sources (Focus 1.1). We correlated findings with a 2-year postoperative outcome.Results: Sixteen patients had seizures with a well-lateralized, regular 5 to 9-Hz rhythm at onset, that most often had a temporal or subtemporal distribution. All patients became seizure free after surgery. In 5 I patients, seizure onset was remarkable for lateralized slow rhythms (<5 Hz), which sometimes appeared as periodic discharges, were often irregular and stable only for short periods (<5 s), and had a widespread lateral temporal distribution. Among these a favorable surgical outcome was encountered in patients with seizures having prominent anterior-tip sources (16 of 17 seizure free), whereas those with dominant lateral or oblique sources had a less favorable outcome (three of 14 and 13 of 18, respectively). Irregular, nonlateralized slowing characterized seizure onsets in eight patients. Three patients became seizure free after surgery.Conclusions: Both visual and quantitative sublobar source analysis of scalp ictal EEG can predict surgical outcome in most cases after AMTL and complement non-invasive presurgical evaluation.

Practice parameter: Temporal lobe and localized neocortical resections for epilepsy

“…In one series, 29 of 35 patients (83%) who were free of disabling seizures since surgery worked full-time, whereas only 6 of 18 patients (33%) with persistent disabling seizures in each year after surgery worked full-time; all patients free of disabling seizures were employed after surgery, while seven of 18 patients (39%) with persistent disabling seizures were unemployed. 60 However, (16)(17)(18)(19)(20)(21)(22)(23)(24)(25) there were conflicting results regarding the net effect of surgery on employment. 14,32,[59][60][61] A series in the United States 60 found that unemployment declined from 25 to 11% and another in Germany 59 found a similar decline from 34 to 16%, but not all individuals who were employed before surgery remained employed afterwards.…”

Brain source montages improve the non-invasive diagnosis in epilepsy

“…As shown also in previous publications on temporal lobe epilepsy [3,4,6], brain source montages provide a better separation of the activities of both hemispheres and the different brain regions as compared with routine bipolar and average reference montages. Thus, focal activities can be recognized more easily as they emerge better above the on-going EEG of the brain region they model.…”

“…the time-varying regional dipole moments that are calculated by a spatial transformation of all surface signals. This transformation of scalp into brain source waveforms [2] separate the activities at the different aspects of the temporal lobe from those at other cortical surfaces [3,4].…”

“…Brain source montages can dissociate the activities of the different lobes, hemispheres and sublobar areas, e.g. the different surfaces of the right and left temporal lobes [3,4,6].…”

Klinischer Stellenwert der Quellenanalyse epileptischer Aktivität

“…Diese identifizierte den Anfallsonset im inferolateralen Kortex, was gut mit den interiktalen Befunden übereinstimmte. Dieselbe Arbeitsgruppe konnte nachweisen, dass die iktale Dipolorientierung und -lokalisation prädik-tiv für das Outcome nach anteromesialer temporaler Lobektomie war [2]. Bei einer tangentialen basalen iktalen Quelle wurden mehr Patienten anfallsfrei.…”