Epilepsy is a disease characterized by spontaneous and abnormal discharges of the nerve cells. It is estimated that approximately 400 000 to 800 000 patients in Germany suffer from epilepsy. Approximately 30 000 new cases occur every year. Epilepsy is often genetically conditioned (idiopathic epilepsy), but other brain diseases, such as brain tumours, inflammation, brain injuries, etc. can also cause epilepsy. In 70% of patients it is possible to treat epilepsy with medication in such a way that no more seizures occur. However, there are also drug-resistant epilepsies in which freedom from seizures cannot be achieved. These patients are potential candidates for epilepsy surgery. Whether these patients are really qualified for surgery will be resolved through special examinations in the Epilepsy Centre. The requirement for an indication for surgery is, apart from resistance to epilepsy drugs, identification of the zone of seizure origin (focus) that is only then surgically removed if postoperative freedom from seizures without additional neurological and mental deficiencies can be predicted with high confidence. The cause of epilepsy with focal seizure origin is often Ammon's horn sclerosis (changes in the hippocampus), abnormalities of development (dysplasias) or tumours (Fig. 1). Particularly epileptogenic are processes in the medial temporal lobe (temporomesial structures such as the hippocampus and amygdala).
In surgically treatable epilepsies simple focal seizures and complex focal seizures can occur. Furthermore, it is possible that both seizure forms will be converted into generalized tonic-clonic seizure (generalized seizure).
In the case of a simple focal seizure consciousness is always retained, i.e. the patient is aware of, for instance, motor tics in the region of the hand or arm that can last 1-2 minutes.
A complex focal seizure is always accompanied with a disturbance of consciousness, i.e. the patient does not react to speech, and has a frozen, empty expression. There can also be mastication and incomprehensible sounds and also to misguided actions. The duration of these seizures is on average one minute; afterwards longer periods of reorientation can occur.
In the case of a focally initiated generalized seizure there occurs, usually originating from a simple or complex focal seizure, sudden unconsciousness with a 30-second long stiffening of arms and legs, followed by convulsions of all extremities, lasting 30-40 seconds. There can be tongue biting and enuresis. Afterwards follows a period of reorientation with a subsequent need for sleep.
Within the pre surgical epilepsy diagnostics numerous examinations are carried out to determine the seizure origin of epilepsy. This comprises video-EEG monitoring with surface electrodes and sphenoidal electrodes, magnetic resonance tomography, blood flow measurement during seizure and after (ictal and interictal SPECT), neuropsychological examinations and the Wada test. If the place of origin of epilepsy cannot be definitely determined in this way, strip electrodes or plate electrodes are inserted under the cerebral membrane in order to record the brain potentials directly from the brain.
A: Ammon's horn sclerosis (arrow).
B: Hippocampal dysplasia (arrows).
C: temporomesial brain tumour (dysembryoplastic neuroepithelial tumour, DNT) (arrows).
Depending on the cause of epilepsy, it is possible to obtain freedom from seizures through epilepsy surgical intervention in approximately 60 to 80% of cases or 90% reduction of seizures. Always, if a circumscribed zone of seizure origin can be located and it is not in a functionally important brain area, surgery is possible. The operations are usually carried out with computer-assisted neuronavigation to be able to accurately plan the surgical access and the extent of resection. During the surgery the resection of the diseased tissue is controlled using navigation. Once the diseased brain tissue is removed, the potentials (electrocorticography) are conducted away from the margins of the adjoining cerebral cortex in order to recognize and then to cut away potentially remaining epileptogenic tissue. Because the inner areas of the temporal lobes are often the cause of epilepsy, the amygdale and hippocampus are removed with or without the adjoining parts of temporal lobes (amygdalohippocampectomy or corticoamygdalohippocampectomy). If a tumour is the cause of epilepsy, usually only the tumour is initially removed. If the electrocorticography still shows seizure activity after removing the tumour, also the adjoining tumour-free brain tissue, if it does not carry any important functions, is removed in order to obtain freedom from seizures.
In some patients seizures start in various places, so that the zone of seizure origin cannot be removed. In these patients implantation of a vagus stimulator can be carried out. In the course of this, an electrode is wound around the left vagus nerve and then the nerve is stimulated via an instigator (Fig. 5). By the use of this technique in approximately 40% of patients the seizure frequency can be permanently reduced by 50%, and 1 - 2% are free of seizures.
A 25-year-old female student suffered initially from generalized seizures. The MRI showed a small blood-filled cavernoma in the postcentral region to the right. The neurological findings were inconspicuous. The electroencephalography (EEG) confirmed cavernoma as the cause of seizures. Through a small, approx. 4 cm craniotomy the cavernoma was microsurgically completely removed under neuronavigational conduct. In the course of this, it was approached through the cerebral sulcus, so that only very little of the normal brain had to be severed in order to reach the cavernoma (watch video). The intraoperative recording of the brain waves after removing the cavernoma showed no seizure potentials. Postoperatively the patient is free of seizures without medications. There are no neurological disturbances.
A: The MRI images show cavernoma with haemorrhage in the postcentral region of the right cerebral hemisphere.
B: Approach planning with neuronavigation.
C: The video shows removal of the tumour through cerebral sulcus access.
D: Recording of brain waves from the cerebral cortex.
E: Electrodes at the edge of the resection cavity.
F: The postoperative T1-weighted MRI images with contrast agent show complete removal of the tumour. The patient is free of complaints 1 year after surgery. Seizures do not occur any more after the surgery (without taking medication).
The 36-year-old female patient had suffered since she was 14 from complex focal seizures that often transferred into generalized seizures. Ultimately, despite pharmacological therapy, approx. 30 seizures per month occurred. The MRI showed typical signs of Ammon's horn sclerosis with atrophy (reduction in size) of the hippocampus and extended temporal horn. Ammon's horn sclerosis is a frequent cause of therapy-resistant seizures. The preoperative epilepsy diagnostics confirmed presence of the cause of seizure in this area. The amygdalae and hippocampus were microsurgically removed through a small opening in the skull (amygdalohippocampectomy). In the course of this it was approached through the cerebral sulcus, so that no normal brain tissue had to be removed in order to reach the hippocampus. The intraoperative recording of brain waves after removing the hippocampus showed no seizure potentials. Postoperatively the patient is free of seizures. Medication was left to ensure safety. There are no neurological or mental disturbances.
A: The MRI images show obvious atrophy of the left-sided hippocampus (long arrows). The temporal horn of the left lateral ventricle is extended (short arrow).
B: Intraoperative electrocorticography.
C: The postoperative MRI images show the selective complete removal of hippocampal formation.
The female patient suffered for the first time at the age of 21 from a generalized seizure. Furthermore, she had experienced for at least 2 years many times per month conditions with an unusual feeling in the stomach region (aura = simple focal seizure) that often transformed into a state of absence lasting about one minute. The mother of the patient reported that in those episodes the patient masticated and had a blank expression (complex focal seizure). The MRI showed a small tumour in the inner part of the right temporal lobe. The video EEG diagnostics confirmed that the tumour was the cause of epilepsy.
The tumour was microsurgically completely removed through a small opening in the skull. In the course of this it was approached through the cerebral sulcus, so that no normal brain tissue had to be removed in order to reach the tumour. It was possible to isolate the tumour from normal brain tissue. The intraoperative recording after the tumour removal was without any manifestations of seizure disposition. Histopathological examination showed that it was a case of benign tumour (dysembryoplastic neuroepithelial tumour). Postoperatively the patient has been free of seizures for 2 years. There are no neurological or mental disturbances. In order to ensure safety anti epileptic monotherapy with lamotrigine is continued.
A: The MRI images show a tumour in the area of the right hippocampal formation (temporomesial tumour) (arrows).
B: Postoperative MRI images 2 years after surgery show complete tumour removal (arrows).
A: Electrode at vagus nerve (arrows)
B: instigator (arrow)