Occipital Lobe Epilepsy: Electroclinical Manifestations, Electrocorticography, Cortical Stimulation and Outcome in 42 Patients Treated Between 1930 and 1991

Abstract

Our study documents the clinical and electrographic findings in 42 patients with medically refractory occipital lobe epilepsy, who underwent surgery at the Montreal Neurological Institute between 1930 and 1991, and the evolving manner in which those patients were studied by successive generations of investigators. In more than two-thirds of the patients the clinical manifestations indicated the occipital onset of the seizures. Seventy-three percent experienced visual aurae, of which elementary hallucinations were the most common and 12 also had ictal blindness. Other occipital manifestations included: contralateral eye deviation, blinking, a sensation of eye movement and nystagmoid eye movements. Intra-operative cortical stimulation elicited a habitual aura in 37% of 29 patients. Lateralizing clinical features were seen in almost two-thirds of patients: contralateral head deviation occurred in half, 59% had visual field defects contralateral to the epileptogenic area and 64% had abnormal imaging studies ipsilateral to the side of surgery. More than one-third of patients exhibited more than one seizure type, suggesting ictal spread to temporal or frontal lobe: 50% had typical temporal lobe automatisms, and 38% exhibited focal motor seizure activity. Surface electroencephalogram (EEG) recordings showed posterior temporal-occipital epileptiform discharges in 46% of patients. Only 18% had electronegative spiking limited to 01 or 02. Large epileptogenic areas were often found on intracranial recording with depth electrodes and on electrocorticography. Pre-excision electrocorticography spiking was restricted to the occipital lobe in only 13 out of 34 patients. More often spiking also involved the posterior temporal and posterior parietal regions. Twenty-three patients underwent only occipital resections; five had only temporal resections, so as to preserve the visual fields, and the remaining 14 patients had extensive resections, which included the posterior temporal or posterior parietal regions. A follow-up period of 1 to 46 yrs (mean 17 yrs) was available for 37 patients. Forty-six percent became seizure free and 21% had a significant reduction in seizure frequency. A better outcome was observed in those patients in whom there was no post-resection electrocorticographic or surface EEG epileptiform discharge, or who exhibited an occipital lobe lesion.

Electrical Cortical Stimulation of the Human Prefrontal Cortex Evokes Complex Visual Hallucinations

“…Moreover, we found the spatial organization of the induced response to be different depending on the site of stimulation within the PFC: The visual reponses evoked on the inferior frontal gyrus were perceived in the whole visual field (as in temporal lobe stimulation), whereas the visual responses on the middle frontal gyrus, bordering the superior frontal sulcus and anterior to the frontal eye field (23), were restricted to the contralateral hemispace. Unilateral complex visual hallucinations have been reported after occipital lobe stimulation, but not in other cortical structures (25,26).…”

Indices of Resective Surgery Effectiveness for Intractable Nonlesional Focal Epilepsy

“…In a study of nonlesional patients, even sequential spikes constituting an ictal discharge failed to identify the ictal-onset region consistently (52). Thus congruency between spike field and region of principal epileptogenesis in some studies (32,53) may reflect the presence of a lesion as the essential linchpin for the relation.…”

Merging Tradition with Innovation: Intraoperative Corticography and 7 Tesla Magnetic Resonance Imaging Sparing Chronic Intracranial Electrode Implantation in "Non-Lesional" Epilepsy Surgery

“…The semiology is variable, the epileptogenic zone is frequently broad and may coexist with hippocampal sclerosis ("dual pathology"), the interictal and ictal patterns multifocal, absent and occasional misleading and the imaging studies often unrevealing [8]. Most of the literature pertaining on the use of ECoG in extratemporal epilepsy stems from lesional cases [9][10][11][12], although prospective studies are lacking [13]. For non lesionalextratemporal resections the data is sparse [14].…”

“…For non lesionalextratemporal resections the data is sparse [14]. The existing data failed to show a clear relationship between the amount of epileptogenic tissue resected and the seizure outcome [10,15].…”