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.

We report the clinical manifestations and outcome of 82 patients with nontumoural parietal lobe epilepsy treated surgically at the Montreal Neurological Institute between 1929 and 1988. Patients with extensive resections extending outside the parietal lobe were excluded. Ninety-four percent exhibited aurae: the most common were somatosensory, described by 52 patients; 13 of these also described pain. Other aurae included disturbances of body image, visual illusions, vertiginous sensations and aphasia or dysphasia. A few patients exhibited complex visual or auditory hallucinations and elementary visual hallucinations. Intraoperative cortical stimulation reproduced the habitual aurae in 44 patients. Often the clinical manifestations indicated ictal spread to the frontal, supplementary motor area, or temporo-limbic areas: 28% of patients exhibited tonic posturing of the extremities, 57% unilateral clonic activity, 17% oral or gestural automatisms and 4% complex automatisms. Sixty-one percent of patients with tonic posturing had epileptogenic zones which included the superior parietal lobe, and in 79% of patients with automatisms the epileptogenic zones extended to the inferior parietal lobe, suggesting different spread patterns. Forty-three patients underwent right, and 39 left parietal corticectomies. Postoperative sensory deficits were seen only when the corticectomy extended into the post-central gyrus. Early in the series extensive nondominant inferior parietal resections led to disturbances of body image in a few patients. Follow-up ranging from 2 to 50 years was available for 79 patients. Sixty-five percent had a complete or nearly complete cessation of seizures. Those patients with no post-resection electrocorticographic epileptiform discharges had a more favourable outcome.

SUMMARY:The serious, late complication of superficial cerebral hemosiderosis, which appears after several years in 1/4–1/3 of patients who have undergone hemispherectomy, has resulted in recent years in a considerable reluctance to carry out this operation despite the fact it has proved to be highly effective in patients with medically refractory seizures associated with hemiplegia. Preservation of a small portion of the hemisphere, usually the frontal or occipital pole, has proved to be effective in preventing this late complication, but at the cost of a significant reduction in the effectiveness of the operation in reducing the patients’ seizure tendency. Preserving the frontal and occipital poles but disconnecting them from the rest of the brain, resulting in a functional complete but anatomical subtotal hemispherectomy, retains the therapeutic effectiveness of a complete hemispherectomy while still protecting adequately against the serious late postoperative complication of superficial cerebral hemosiderosis and its associated neurologic deterioration, hydrocephalus and sometimes death.

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