Multiple hippocampal transections for intractable hippocampal epilepsy: Seizure outcome.

PURPOSE: The purpose of this study was to evaluate the seizure outcomes after transverse multiple hippocampal transections (MHTs) in 13 patients with intractable TLE. METHODS: Thirteen patients with normal memory scores, including 8 with nonlesional hippocampi on MRI, had temporal lobe epilepsy (TLE) necessitating depth electrode implantation. After confirming hippocampal seizure onset, they underwent MHT. Intraoperative monitoring was done with 5-6 hippocampal electrodes spaced at approximately 1-cm intervals and spike counting for 5-8min before each cut. The number of transections ranged between 4 and 7. Neuropsychological assessment was completed preoperatively and postoperatively for all patients and will be reported separately. RESULTS: Duration of epilepsy ranged between 5 and 55years. There were no complications. Intraoperatively, MHT resulted in marked spike reduction (p=0.003, paired t-test). Ten patients (77%) are seizure-free (average follow-up was 33months, range 20-65months) without medication changes. One of the 3 patients with persistent seizures had an MRI revealing incomplete transections, another had an additional neocortical seizure focus (as suggested by pure aphasic seizures), and the third had only 2 seizures in 4years, one of which occurred during antiseizure medication withdrawal. Verbal and visual memory outcomes will be reported separately. Right and left hippocampal volumes were not different preoperatively (n=12, p=0.64, Wilcoxon signed-rank test), but the transected hippocampal volume decreased postoperatively (p=0.0173). CONCLUSIONS: Multiple hippocampal transections provide an effective intervention and a safe alternative to temporal lobectomy in patients with hippocampal epilepsy.

Homotopic reciprocal functional connectivity between anterior human insulae.

The aim of this study was to investigate functional connectivity between right and left insulae in the human brain. We studied a patient with implanted depth electrodes for epilepsy surgery evaluation with stereotactically placed symmetric depth electrodes in both insulae. Bipolar 1 Hz electrical stimulation of the right and left posterior short gyri in the anterior insula evoked responses in the contralateral insular structures. These responses showed a latency of 8-24 ms. This report demonstrates for the first time bi-directional homotopic and heterotopic functional connectivity between right and left anterior insulae. The short latency of the evoked responses suggests mono- or oligo-synaptic connections, most likely via the corpus callosum.

Functional connectivity between right and left mesial temporal structures.

The aim of this study is to investigate functional connectivity between right and left mesial temporal structures using cerebrocerebral evoked potentials. We studied seven patients with drug-resistant focal epilepsy who were explored with stereotactically implanted depth electrodes in bilateral hippocampi. In all patients cerebrocerebral evoked potentials evoked by stimulation of the fornix were evaluated as part of a research project assessing fornix stimulation for control of hippocampal seizures. Stimulation of the fornix elicited responses in the ipsilateral hippocampus in all patients with a mean latency of 4.6 ms (range 2-7 ms). Two patients (29 %) also had contralateral hippocampus responses with a mean latency of 7.5 ms (range 5-12 ms) and without involvement of the contralateral temporal neocortex or amygdala. This study confirms the existence of connections between bilateral mesial temporal structures in some patients and explains seizure discharge spreading between homotopic mesial temporal structures without neocortical involvement.

Low-frequency electrical stimulation of a fiber tract in temporal lobe epilepsy.

OBJECTIVE: Surgical resection of the temporal lobe is an effective treatment for medically intractable temporal lobe epilepsy, but can cause memory impairment. Deep brain stimulation in epilepsy has targeted gray matter structures using high frequencies, but achieved limited success. We tested the hypothesis that low-frequency stimulation of the fornix reduces interictal epileptiform discharges and seizures in patients with intractable mesial temporal lobe epilepsy, without affecting memory. METHODS: We implanted depth electrodes in 11 patients for surgical evaluation of intractable epilepsy. Low-frequency stimulation of the fornix occurred in 4-hour sessions in the video-electroencephalography unit. Mental status assessment was performed at baseline and during stimulation. We studied the effect of stimulation on hippocampal spikes and seizures. RESULTS: There were no complications, and the patients were unaware of the stimulation. Fornix stimulation elicited evoked responses in the hippocampus and the posterior cingulate gyrus. Hourly Mini-Mental Status Examination (MMSE) scores showed an increase during stimulation when compared to prestimulation MMSE, largely due to improvement in recall, possibly representing a practice effect. Hippocampal spikes were significantly reduced during and outlasting each stimulation session. Seizure odds (n = 7) were reduced by 92% in the 2 days that followed stimulation. INTERPRETATION: Low-frequency stimulation of the fornix activates the hippocampus and other areas of the declarative memory circuit. The results of this preliminary study suggest that low-frequency stimulation is tolerable and reduces epileptiform discharges and seizures in patients with intractable mesial temporal lobe epilepsy. A controlled clinical trial may be warranted.

Can semiology predict psychogenic nonepileptic seizures? A prospective study.

OBJECTIVE: Reducing health and economic burdens from diagnostic delay of psychogenic nonepileptic seizures (PNES) requires prompt referral for video electroencephalography (VEEG) monitoring, the diagnostic gold standard. Practitioners make VEEG referrals when semiology suggests PNES, although few semiological signs are supported by well-designed studies, and most VEEG studies neglect to concurrently measure how accurately seizure witnesses can ascertain semiology. In this study, we estimate the value of eyewitness-reported and video-documented semiology for predicting PNES, and we measure accuracy of eyewitness reports. METHODS: We prospectively interviewed eyewitnesses of seizures in patients referred for VEEG monitoring, to inquire about 48 putative PNES and ES signs. Multiple, EEG-blinded, epileptologists independently evaluated seizure videos and documented the presence/absence of signs. We used generalized estimating equations to identify reliable video-documented PNES and ES signs, and we compared eyewitness reports with video findings to assess how accurately signs are reported. We used logistic regression to determine whether eyewitness reports could predict VEEG-ascertained seizure type. RESULTS: We analyzed 120 seizures (36 PNES, 84 ES) from 35 consecutive subjects. Of 45 video-documented signs, only 3 PNES signs ("preserved awareness," "eye flutter," and "bystanders can intensify or alleviate") and 3 ES signs ("abrupt onset," "eye-opening/widening," and postictal "confusion/sleep") were significant and reliable indicators of seizure type. Eyewitness reports of these 6 signs were inaccurate and not statistically different from guessing. Consequentially, eyewitness reports of signs did not predict VEEG-ascertained diagnosis. We validated our findings in a second, prospective cohort of 36 consecutive subjects. INTERPRETATION: We identified 6 semiological signs that reliably distinguish PNES and ES, and found that eyewitness reports of these signs are unreliable. We offer suggestions to improve the accuracy of eyewitness reports.