Surgical Treatment

In all patients with persistent epilepsy unrelieved by AED treatment, it is appropriate to consider surgical intervention. The aim of epilepsy surgery is the removal of the epileptogenic brain tissue in order to achieve seizure control without causing additional iatrogenic deficits. Only in rare cases, such as those with diffuse pathology and catastrophic seizures, are palliative surgical procedures performed. Approximately one-third of patients with refractory epilepsy are suitable for epilepsy surgery. The prerequisites of surgery are frequent epileptic seizures and a minimum of 3-5 years of unsuccessful AED treatment including at least two first-line AEDs in monotherapy and combination. This is a minimal condition that only applies to patients who are ideal candidates for epilepsy surgery. These are patients with unilateral mesial temporal lobe epilepsy and hippocampal sclerosis, extratemporal epilepsies with localized structural lesions, and some types of catastrophic epilepsies in childhood. The poorer the individual prognosis of surgery, the longer the requested presurgical attempts to achieve seizure control with AEDs and complimentary nonsurgical treatments.

1. Presurgical Assessment

Treatment centers that engage in routine surgical management of epilepsy generally have a standardized assessment process for patients being considered for such treatment. Although the program may vary between centers, the general procedure is similar. A first hypothesis with respect to the suspected epilepto-genic region is based on clinical history, neurological examination, and interictal EEG. These procedures focus particularly on searching for etiological factors, evidence of localizing signs and symptoms, and a witnessed description of the seizures. In addition, psychosocial information must be gathered relating to education, employment, social support, and past and present mental state findings. In a second step of presurgical assessment, all patients undergo more specific investigations. In general, these include several days of continuous video telemetry using surface electrodes. The aim of telemetry is to obtain multiple ictal recordings, which give more valuable localizing information than interictal records. Often, patients will reduce their AED prior to telemetry in order to facilitate the occurrence of seizures. Recent advances in structural and functional neuroimaging have made invasive EEG recording less necessary. MRI using optimized techniques has increased the sensitivity for the detection of subtle structural lesions not seen on CCT and standard MRI and is now used routinely. Functional imaging techniques using SPECT and PET are used to further delineate the epileptogenic region. If results from all investigations are concordant, patients will have surgery. If results are discordant, invasive EEG recordings using subdural grid electrodes or intracerebral depth electrodes may be applied in order to identify the critical epileptogenic region.

All patients being considered for epilepsy surgery should have a neuropsychological assessment. This is important both to detect focal brain dysfunction and to predict the results of surgery, especially temporal lobe surgery. The intelligence quotient may be measured using the Wechsler Adult Intelligence Scale. In some centers a score of less than 75 has been taken as evidence of diffuse neurological disorder and, hence, as a relative contraindication to surgery. It is important before proceeding to surgery to investigate the hemispheric localization of language and memory. This is generally performed using the Wada test. Sodium amylobarbitone is injected into one internal carotid artery, and while that hemisphere is briefly suppressed language and memory tests are performed. The procedure is then repeated for the other hemisphere.

2. Surgical Procedures

Many surgical procedures have been developed. Most patients who undergo surgery suffer from temporal lobe epilepsy. Most of these patients undergo one of two standard procedures: two-thirds anterior resection or amygdala hippocampectomy. In extratemporal epilepsies, lobectomies, lesionectomies, or individually "tailored" topectomies are performed. The latter techniques may involve preoperative stimulation in order to identify eloquent brain tissue that should be preserved from resection. A palliative method that can be applied in functionally crucial cortical regions is multiple subpial resections, which interrupt intracortical connections without destroying the neuronal columns that are necessary for normal cerebral function. Another palliative method that is performed mainly in patients with epileptic falls is anterior or total callosotomy.

3. Prognosis and Complications

The outcome of epilepsy surgery is classified according to four categories: class 1, no disabling seizures; class 2, almost seizure free; class 3, clinical improvement; and class 4, no significant improvement. According to a meta-analysis of 30 surgical series with a total of 1651 patients, seizure outcome is as follows: class 1, 59%; class 2, 14%; class 3, 15%; and class 4, 12%. In this study, predictors of a good surgical outcome were febrile seizures, complex partial seizures, low preopera-tive seizure frequency, lateralized interictal EEG findings, unilateral hippocampal pathology on MRI, and neuropathological diagnosis of hippocampal sclerosis. Predictors for a poor outcome were generalized seizures, diffuse pathology on MRI, normal histology of removed tissue, and early postoperative seizures.

Relative contraindications for temporal lobe resections are extensive or multiple lesions, bilateral hippocampal sclerosis or dual pathology within one temporal lobe, significant cognitive deficits, interictal psychosis, multiple seizure types, extratemporal foci in the interictal EEG, and normal MRI. The ideal patient has mesial temporal lobe epilepsy due to unilateral hippocampal sclerosis of the nondominant hemisphere. A negative MRI decreases the chances of surgery for seizure control and a focus in the dominant hemisphere increases the risk of postoperative neu-ropsychological deficits.

The nature of potential perioperative complications and postsurgical neurological, cognitive, and psychiatric sequelae depends in part on the site of surgery. Operative complications occur in less than 5% of patients. In two-thirds of patients who undergo temporal resection of the dominant hemisphere, verbal memory is impaired. Another possible complication of epilepsy surgery is psychiatric disorder. Only rarely does this manifest as de novo psychosis. Many patients, however, will go through a phase of depression and increased anxiety following surgery. Therefore, most surgery centers include a psychiatric assessment in the preoperative phase and also a psychiatric follow-up in order to avoid catastrophic reactions (including suicide) to either the failure of surgery or the success of surgery, which requires far-reaching psychosocial adjustment.

4. Vagal Nerve Stimulation

A different surgical approach is that of vagal nerve stimulation (VNS) using an implanted stimulator. This approach has the drawback that while the nerve is being stimulated, usually for 30 sec every 5-10 min, the voice changes. More intense stimulation may be associated with throat pain or coughing. Nevertheless, in one series of 130 patients, mean seizure frequency decreased by 30% after 3 months and by 50% after 1 year of therapy. Altogether, 60-70% of the patients showed some response, but seizure freedom has rarely been achieved. Therefore, VNS is only indicated in patients who are pharmacoresistant and who are not suitable for resective epilepsy surgery.

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