The most favorable candidates for surgery are those with focal seizures that induce altered consciousness and a unilateral temporal lobe focus. In this group, rates of cure and significant improvement approach 90 percent in some series but overall, are probably closer to 50 percent after 5 years. A randomized trial conducted by Wiebe and colleagues gave representative results after temporal lobectomy of 58 percent of 40 carefully studied patients remaining seizure-free after 1 year, in contrast to 8 percent on medication alone. Furthermore, as reported by Yoon and colleagues, among those patients who remain free of seizures for 1 year after surgery, more than half are still free of seizures after 10 years and most of the remainder had one or fewer episodes per year. It should be emphasized that most of the patients who underwent surgery in these studies still required anticonvulsant medication. Even in the special group of patients with temporal lobe foci who have no lesion on MRI but have subtle signal changes in the hippocampus, Bell et al report that 60 percent of patients can be made free of disabling seizures with surgery.
Excision of cortical tissue that contains a structural lesion outside of the temporal lobe accomplishes complete seizure-free states in approximately 50 percent. Taking all seizure types together, only approximately 10 percent of patients obtain no improvement at all and less than 5 percent are worse. The matter of resection of areas of focal cortical dysplasias in children is a highly specialized area. It has been indicated that the histologic features of the dysplasia are important determinants of the success of surgery (Fauser et al).
Other surgical procedures of value in highly selected cases are sectioning of the corpus callosum, which is for the most part palliative, and hemispherectomy, which may be curative in special circumstances. The most encouraging results with callosotomy have been obtained in the control of intractable partial and secondarily generalized seizures, particularly when atonic drop attacks are the most disabling seizure type. Removal of the entire cortex of one hemisphere, in addition to the amygdala and hippocampus, has been of value in children, as well as in some adults with severe and extensive unilateral cerebral disease and intractable contralateral motor seizures and hemiplegia. Rasmussen encephalitis, Sturge-Weber disease, and large porencephalic cysts at times fall into this category. Surgical, focused radiation, or endovascular reduction of arteriovenous malformations may reduce the frequency of seizures, but the results in this regard are somewhat unpredictable (see Chap. 34).
This technique has found some favor in cases of intractable partial and secondarily generalizing seizures. A pacemaker-like device is implanted in the anterior chest wall and stimulating electrodes are connected to the vagus at the left carotid bifurcation. The procedure is well tolerated except for hoarseness in some cases. Several trials have demonstrated an average of 25 percent reduction in seizure frequency among patients who were resistant to all manner of anticonvulsant drugs (see Chadwick for a discussion of clinical trials). The mechanism by which vagal stimulation produces its effects is unclear, and its role in the management of seizures is still being defined. Stimulation of the cerebellum and of other sites in the brain has also been used in the control of seizures, with no clear evidence of success. They must currently be considered to be experimental.