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 occured 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, suggestion 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 intractranial recording with depth electrodes and on electrocorticography. Preexcision 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.