Long-term seizure outcome in frontal lobe epilepsy surgery

The Fingerprint of Scalp-EEG in Drug-Resistant Frontal Lobe Epilepsies

PURPOSE

Scalp-EEG incompletely covers the frontal lobe cortex. Underrepresentation of frontobasal or frontomesial structures, fast ictal spreading, and false lateralization impede scalp-EEG interpretation. Hence, we investigated the significance of scalp-EEG in the presurgical workup of frontal lobe epilepsy.

METHODS

Using descriptive statistical methods and Pearson chi-squared test for group comparisons, we retrospectively investigated postsurgical outcome, interictal epileptiform discharges (iiEDs), and electrographic seizure patterns on scalp-EEG in 81 consecutive patients undergoing resective epilepsy surgery within the margins of the frontal lobe.

RESULTS

Postoperatively, patients with frontopolar iiEDs (n = 7) or concordant frontopolar iiED focus and seizure-onset (n = 2) were seizure free (n = 7/7, Engel Ia). MRI-positive patients with frontopolar iiEDs or frontopolar seizure-onset (n = 1/8 Engel Id, n = 7/8 Engel Ia) underwent surgery without stereo-EEG. Thirteen of 16 patients with frontolateral (n = 8/10, Engel Ia), or left frontobasal (n = 5/6, Engel Ia) seizure-onset undergoing further stereo-EEG, were seizure-free postoperatively. Seizure-onset prevalent over one electrode (n = 37/44 Engel I, p = 0.02), fast activity (FA)/flattening at seizure-onset (n = 29/33 Engel I, p = 0.02), FA/flattening during the seizure (n = 38/46 Engel I, p = 0.05), or focal rhythmic sharp-/spike-/polyspike-and-slow waves during the seizure (n = 24/31, Engel Ia, p = 0.05) were favorable prognostic markers. Interictal polyspike waves (p = 0.006 for Engel Ia) and interictal paroxysmal FA (p = 0.02 for Engel I) were unfavorable prognostic markers.

CONCLUSIONS

Frontopolar scalp-EEG findings serve as biomarkers for predicting favorable surgical outcome in lesional frontal lobe epilepsy. Consequently, careful analysis of scalp-EEG assists in bypassing stereo-EEG in these patients.

Automated analysis of cortical volume loss predicts seizure outcomes after frontal lobectomy

OBJECTIVE

Patients undergoing frontal lobectomy demonstrate lower seizure-freedom rates than patients undergoing temporal lobectomy and several other resective interventions. We attempted to utilize automated preoperative quantitative analysis of focal and global cortical volume loss to develop predictive volumetric indicators of seizure outcome after frontal lobectomy.

METHODS

Ninety patients who underwent frontal lobectomy were stratified based on seizure freedom at a mean follow-up time of 3.5 (standard deviation [SD] 2.5) years. Automated quantitative analysis of cortical volume loss organized by distinct brain region and laterality was performed on preoperative T1-weighted magnetic resonance imaging (MRI) studies. Univariate statistical analysis was used to select potential predictors of seizure freedom. Backward variable selection and multivariate logistical regression were used to develop models to predict seizure freedom.

RESULTS

Forty-eight of 90 (53.3%) patients were seizure-free at the last follow-up. Several frontal and extrafrontal brain regions demonstrated statistically significant differences in both volumetric cortical volume loss and volumetric asymmetry between the left and right sides in the seizure-free and non-seizure-free cohorts. A final multivariate logistic model utilizing only preoperative quantitative MRI data to predict seizure outcome was developed with a c-statistic of 0.846. Using both preoperative quantitative MRI data and previously validated clinical predictors of seizure outcomes, we developed a model with a c-statistic of 0.897.

SIGNIFICANCE

This study demonstrates that preoperative cortical volume loss in both frontal and extrafrontal regions can be predictive of seizure outcome after frontal lobectomy, and models can be developed with excellent predictive capabilities using preoperative MRI data. Automated quantitative MRI analysis can be quickly and reliably performed in patients with frontal lobe epilepsy, and further studies may be developed for integration into preoperative risk stratification.

Seizure outcome and its predictors after frontal lobe epilepsy surgery

OBJECTIVES

Frontal lobe epilepsy (FLE) surgery is the second most common focal resective surgery for drug-resistant epilepsy. Not many studies are available regarding the long-term surgical outcome of FLE. We studied the longitudinal outcome and predictors of seizure outcome following FLE surgery in a sizeable cohort of patients.

MATERIALS & METHODS

A total of 73 consecutive patients who underwent FLE surgery between January 1997 and May 2015 with a minimum follow-up of 1 year (range 1-16 years) were studied. Primary outcome was seizure freedom at last follow-up (Engel Class IA). "Seizure freedom" separately was defined as absence of seizures till last follow-up. Outcome predictors were subjected to multivariate analysis. Using Kaplan-Meier curve, we assessed the post-operative seizure freedom over time.

RESULTS

Twenty-five patients (34%) were seizure-free till last follow-up. The seizure freedom was 45%, 34%, 26%, 20% and 14% at the end of 1st, 2nd, 3rd, 4th and 5th post-operative year, respectively. Engel class I outcomes were 48%, 41%, 56%, 57% and 53% at end of 1st, 2nd, 3rd, 4th and 5th post-operative year, respectively. Predictors of seizure recurrence on multivariate analysis were older age at surgery (P = 0.032), longer duration of epilepsy (P = 0.031), presence of interictal epileptiform discharges in post-operative EEG on 7th day (P = 0.005), 3 months (P = 0.005) and 1 year (P = 0.0179). In subgroup analysis, duration of epilepsy of less than 2 years before surgery was a significant predictor for achieving seizure freedom (P = 0.029).

CONCLUSIONS

These results emphasize early surgery for better outcome in frontal lobe epilepsy. Post-operative EEG remained a good predictor for long-term outcome.