The Effects on Cognitive Performance of Tailored Resection in Surgery for Nonlesional Mesiotemporal Lobe Epilepsy

Abstract

Summary: Purpose: Mesiotemporal lobe epilepsy (MTLE) can be treated with different surgical approaches. In tailored resec- tions, neocortex is removed beyond "standard" margins when spikes are present in the electrocorticogram. We hypothesized that these larger resections are justified because spiking neo- cortex is dysfunctional. This would imply that in patients with spikes (a) postoperative cognitive performance is not affected, and (b) preoperative performance is worse than without spikes. Methods: We studied 80 operated-on MTLE patients with pathologically confirmed nonlesional hippocampal sclerosis. All patients were left-sided language dominant and underwent cog- nitive tests 6 months pre- and postoperatively. A repeated mea- sures analysis of variance (ANOVA) was performed, looking for within- and between-subjects interactions with presence of intraoperative neocortical spikes. Results: Intraoperatively, neocortical spikes were present in 61% of patients. Improved postoperative cognitive outcome was seen only in left-sided patients with spikes. Their performance IQ (PIQ) increased by 8.1 points (95% confidence interval, 3.8- 12.3; p = 0.02), and visual naming latency by 12.8 s (95% CI, 2.1-23.5; p = 0.07). Conversely, in left-sided patients without spikes, naming latency declined by 7.5 s (95% CI, −2.3-17.2; p = 0.07). Preoperative scores were comparable except for a 15.3-point (95% CI, 0.1-30.5; p = 0.02) lower VIQ in left-sided patients without spikes. Conclusions: Tailoring does not harm cognitive performance and is, in left-sided MTLE, associated with postoperative im- provement. Left-sided MTLE without neocortical spikes has lower verbal scores, which tend to decline after standard resection and may represent a special pathophysiologic en- tity. Ke yW ords: Mesiotemporal lobe epilepsy—Epilepsy surgery—Electrocorticography—Neuropsychology. The syndrome of nonlesional mesiotemporal lobe epilepsy (MTLE) is well recognized and a principal tar- get for epilepsy surgery worldwide (1). The syndrome is defined by a set of clinical, interictal, and ictal EEG and magnetic resonance imaging (MRI) criteria. Resection of the amygdala and the hippocampus is the mainstay of its surgical treatment, as archicortical structural changes in the mesial temporal lobe (sclerosis and atrophy) are held critical to seizure propagation in the majority of cases (2). However, coexisting independent spiking in the basal and lateral temporal neocortex have been known in the EEG literature for a long time (3). It has been proposed that in some of these cases, mesiotemporal pathology may be the consequence rather than the cause of epilepsy. Some authors confirmed the presence of microscopic neocor- tical abnormalities that were not seen in MRI (4). The