To establish whether transcranial magnetic stimulation is able to activate the primary epileptic focus preferentially, 13 patients who had medically intractable complex partial seizures were examined prior to surgical therapy. Single or a series of magnetic stimuli were applied to various regions of the skull. The effects of transcranial magnetic stimulation were monitored via subdurally implanted electrodes. In the process of presurgical evaluation, the dosage of anticonvulsant medication had been reduced in all patients but one. Transcranial magnetic stimulation was able to activate the epileptic focus (or foci) in 12 of the 13 patients. Distinct patterns of focal activation were observed in 3 patients who had several foci. No epileptiform potentials were induced outside epileptic foci, which had been identified by corticographic recordings. In one patient a complex partial seizure that was induced was identical to her habitual seizures. In another patient, a complete transition from a nonactive theta focus to a self-sustained epileptic focus occurred. A facilitation of epileptiform afterdischarge was seen with sequential stimulation. No adverse effects were either reported by the patients or observed by the investigators. In summary transcranial magnetic stimulation is able to activate the epileptic focus (or foci) and consequently may be an additional tool for the localization of epileptic foci in presurgical evaluation.
In the choice of anaesthetics and techniques the danger of a possible progressive increase of intracranial pressure (ICP) should be considered. Therefore the influence of intravenous anaesthetic agents on mean arterial pressure, ICP, and cerebral perfusion pressure (CPP) in patients with primarily increased ICP was observed under standard conditions for 20-40 minutes. Etomidate, thiopentone, propanidid, and ketamine showed remarkable effects on ICP, even in patients with disturbed cerebro-vascular reactivity. Etomidate and thiopentone cause a fall of ICP by 26%. Because of its stabilizing effects on circulation etomidate does not induce a reduction of CPP, whereas thiopentone will do so because of its depressing effect on blood pressure. Propanidid appears to be a less suitable agent when there is raised ICP, because it induces fluctuations of ICP and blood pressure up to the third minute after injection. According to our results, monoanaesthesia with ketamine cannot be recommended when there is increased ICP because it causes a prolonged increase in ICP, and reduction of blood pressure and CPP.
An alternative technique for so-called functional hemispherectomy has been developed to be used for the classical indications of hemispherectomy or the various modifications of functional hemispherectomy. The technique entails a smaller trepanation, less operation time, and less blood loss, and it leaves more brain tissue in place as compared with other functional hemispherectomy techniques. It starts with either hippocampectomy alone or with hippocampectomy and anterior temporal lobectomy. After this, deafferentation of the white matter of the temporal, occipital, parietal, and frontal lobe, using either a transcortical transventricular approach along the outline of the lateral ventricle or a sylvian key hole approach, is performed. The technique includes a transventricular callosotomy, and it leaves in place only a small portion of the suprainsular cortex and the insular cortex. However, as one modification, removal of the insular cortex can easily be performed, if necessary, and, as a second modification, the entire transventricular deafferentation can be performed through a sylvian key hole. In this report, the technique is described and the surgical experience for the first 13 patients is outlined. The immediate seizure relief with an average follow-up of 12 months was similar to that for patients with functional hemispherectomy, but the follow-up period for these 13 patients is not long enough to allow definite conclusions concerning long-term control of seizures and long-term complications.
An alternative technique for so-called functional hemispherectomy has been developed to be used for the classical indications of hemispherectomy or the various modifications of functional hemispherectomy. The technique entails a smaller trepanation, less operation time, and less blood loss, and it leaves more brain tissue in place as compared with other functional hemispherectomy techniques. It starts with either hippocampectomy alone or with hippocampectomy and anterior temporal lobectomy. After this, deafferentation of the white matter of the temporal, occipital, parietal, and frontal lobe, using either a transcortical transventricular approach along the outline of the lateral ventricle or a sylvian key hole approach, is performed. The technique includes a transventricular callosotomy, and it leaves in place only a small portion of the suprainsular cortex and the insular cortex. However, as one modification, removal of the insular cortex can easily be performed, if necessary, and, as a second modification, the entire transventricular deafferentation can be performed through a sylvian key hole. In this report, the technique is described and the surgical experience for the first 13 patients is outlined. The immediate seizure relief with an average follow-up of 12 months was similar to that for patients with functional hemispherectomy, but the follow-up period for these 13 patients is not long enough to allow definite conclusions concerning long-term control of seizures and long-term complications.
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